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[PATCH v2 00/11] DAX fsynx/msync support

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  [PATCH v2 00/11] DAX fsynx/msync support Ross Zwisler <ross.zwisler@linux.intel.com> - 2015-11-14 01:10 +0100
    [PATCH v2 09/11] ext2: add support for DAX fsync/msync Ross Zwisler <ross.zwisler@linux.intel.com> - 2015-11-14 01:10 +0100
    [PATCH v2 07/11] mm: add find_get_entries_tag() Ross Zwisler <ross.zwisler@linux.intel.com> - 2015-11-14 01:10 +0100
      Re: [PATCH v2 07/11] mm: add find_get_entries_tag() Dave Chinner <david@fromorbit.com> - 2015-11-16 23:50 +0100
        Re: [PATCH v2 07/11] mm: add find_get_entries_tag() Ross Zwisler <ross.zwisler@linux.intel.com> - 2015-11-17 19:20 +0100
    [PATCH v2 10/11] ext4: add support for DAX fsync/msync Ross Zwisler <ross.zwisler@linux.intel.com> - 2015-11-14 01:10 +0100
    [PATCH v2 11/11] xfs: add support for DAX fsync/msync Ross Zwisler <ross.zwisler@linux.intel.com> - 2015-11-14 01:10 +0100
      Re: [PATCH v2 11/11] xfs: add support for DAX fsync/msync Dave Chinner <david@fromorbit.com> - 2015-11-17 00:20 +0100
        Re: [PATCH v2 11/11] xfs: add support for DAX fsync/msync Ross Zwisler <ross.zwisler@linux.intel.com> - 2015-11-17 20:10 +0100
          Re: [PATCH v2 11/11] xfs: add support for DAX fsync/msync Dave Chinner <david@fromorbit.com> - 2015-11-20 01:50 +0100
    [PATCH v2 05/11] mm: add follow_pte_pmd() Ross Zwisler <ross.zwisler@linux.intel.com> - 2015-11-14 01:20 +0100
    [PATCH v2 01/11] pmem: add wb_cache_pmem() to the PMEM API Ross Zwisler <ross.zwisler@linux.intel.com> - 2015-11-14 01:20 +0100
    [PATCH v2 08/11] dax: add support for fsync/sync Ross Zwisler <ross.zwisler@linux.intel.com> - 2015-11-14 01:20 +0100
      Re: [PATCH v2 08/11] dax: add support for fsync/sync Dave Chinner <david@fromorbit.com> - 2015-11-17 00:00 +0100
        Re: [PATCH v2 08/11] dax: add support for fsync/sync Ross Zwisler <ross.zwisler@linux.intel.com> - 2015-11-17 19:40 +0100
    [PATCH v2 03/11] pmem: enable REQ_FUA/REQ_FLUSH handling Ross Zwisler <ross.zwisler@linux.intel.com> - 2015-11-14 01:20 +0100
      Re: [PATCH v2 03/11] pmem: enable REQ_FUA/REQ_FLUSH handling Dan Williams <dan.j.williams@intel.com> - 2015-11-14 01:30 +0100
        Re: [PATCH v2 03/11] pmem: enable REQ_FUA/REQ_FLUSH handling Andreas Dilger <adilger@dilger.ca> - 2015-11-14 01:50 +0100
          Re: [PATCH v2 03/11] pmem: enable REQ_FUA/REQ_FLUSH handling Dan Williams <dan.j.williams@intel.com> - 2015-11-14 03:40 +0100
            Re: [PATCH v2 03/11] pmem: enable REQ_FUA/REQ_FLUSH handling Jan Kara <jack@suse.cz> - 2015-11-16 14:40 +0100
              Re: [PATCH v2 03/11] pmem: enable REQ_FUA/REQ_FLUSH handling Jan Kara <jack@suse.cz> - 2015-11-16 15:20 +0100
                Re: [PATCH v2 03/11] pmem: enable REQ_FUA/REQ_FLUSH handling Dan Williams <dan.j.williams@intel.com> - 2015-11-16 18:30 +0100
                  Re: [PATCH v2 03/11] pmem: enable REQ_FUA/REQ_FLUSH handling Ross Zwisler <ross.zwisler@linux.intel.com> - 2015-11-16 20:50 +0100
                    Re: [PATCH v2 03/11] pmem: enable REQ_FUA/REQ_FLUSH handling Dan Williams <dan.j.williams@intel.com> - 2015-11-16 21:40 +0100
                      Re: [PATCH v2 03/11] pmem: enable REQ_FUA/REQ_FLUSH handling Ross Zwisler <ross.zwisler@linux.intel.com> - 2015-11-17 01:00 +0100
                Re: [PATCH v2 03/11] pmem: enable REQ_FUA/REQ_FLUSH handling Dave Chinner <david@fromorbit.com> - 2015-11-16 23:20 +0100
                  Re: [PATCH v2 03/11] pmem: enable REQ_FUA/REQ_FLUSH handling Ross Zwisler <ross.zwisler@linux.intel.com> - 2015-11-17 00:30 +0100
                    Re: [PATCH v2 03/11] pmem: enable REQ_FUA/REQ_FLUSH handling Dave Chinner <david@fromorbit.com> - 2015-11-17 00:50 +0100
            Re: [PATCH v2 03/11] pmem: enable REQ_FUA/REQ_FLUSH handling Ross Zwisler <ross.zwisler@linux.intel.com> - 2015-11-16 21:10 +0100
              Re: [PATCH v2 03/11] pmem: enable REQ_FUA/REQ_FLUSH handling Jan Kara <jack@suse.cz> - 2015-11-18 11:50 +0100
                Re: [PATCH v2 03/11] pmem: enable REQ_FUA/REQ_FLUSH handling Ross Zwisler <ross.zwisler@linux.intel.com> - 2015-11-18 17:20 +0100
    [PATCH v2 06/11] mm: add pgoff_mkclean() Ross Zwisler <ross.zwisler@linux.intel.com> - 2015-11-14 01:20 +0100
    [PATCH v2 02/11] mm: add pmd_mkclean() Ross Zwisler <ross.zwisler@linux.intel.com> - 2015-11-14 01:20 +0100
      Re: [PATCH v2 02/11] mm: add pmd_mkclean() Dave Hansen <dave.hansen@intel.com> - 2015-11-14 02:10 +0100
        Re: [PATCH v2 02/11] mm: add pmd_mkclean() Ross Zwisler <ross.zwisler@linux.intel.com> - 2015-11-17 19:00 +0100
    [PATCH v2 04/11] dax: support dirty DAX entries in radix tree Ross Zwisler <ross.zwisler@linux.intel.com> - 2015-11-14 01:20 +0100
    Re: [PATCH v2 00/11] DAX fsynx/msync support Jan Kara <jack@suse.cz> - 2015-11-16 15:50 +0100
      Re: [PATCH v2 00/11] DAX fsynx/msync support Dan Williams <dan.j.williams@intel.com> - 2015-11-16 18:00 +0100
        Re: [PATCH v2 00/11] DAX fsynx/msync support Ross Zwisler <ross.zwisler@linux.intel.com> - 2015-11-16 21:10 +0100

Page 1 of 2  [1] 2  Next page →

#1269363 — [PATCH v2 00/11] DAX fsynx/msync support

This patch series adds support for fsync/msync to DAX.

Patches 1 through 7 add various utilities that the DAX code will eventually
need, and the DAX code itself is added by patch 8.  Patches 9-11 update the
three filesystems that currently support DAX, ext2, ext4 and XFS, to use
the new DAX fsync/msync code.

These patches build on the recent DAX locking changes from Dave Chinner,
Jan Kara and myself.  Dave's changes for XFS and my changes for ext2 have
been merged in the v4.4 window, but Jan's are still unmerged.  You can grab
them here:

http://www.spinics.net/lists/linux-ext4/msg49951.html

Ross Zwisler (11):
  pmem: add wb_cache_pmem() to the PMEM API
  mm: add pmd_mkclean()
  pmem: enable REQ_FUA/REQ_FLUSH handling
  dax: support dirty DAX entries in radix tree
  mm: add follow_pte_pmd()
  mm: add pgoff_mkclean()
  mm: add find_get_entries_tag()
  dax: add support for fsync/sync
  ext2: add support for DAX fsync/msync
  ext4: add support for DAX fsync/msync
  xfs: add support for DAX fsync/msync

 arch/x86/include/asm/pgtable.h |   5 ++
 arch/x86/include/asm/pmem.h    |  11 ++--
 drivers/nvdimm/pmem.c          |   3 +-
 fs/block_dev.c                 |   3 +-
 fs/dax.c                       | 140 +++++++++++++++++++++++++++++++++++++++--
 fs/ext2/file.c                 |  14 ++++-
 fs/ext4/file.c                 |   4 +-
 fs/ext4/fsync.c                |  12 +++-
 fs/inode.c                     |   1 +
 fs/xfs/xfs_file.c              |  18 ++++--
 include/linux/dax.h            |   6 ++
 include/linux/fs.h             |   1 +
 include/linux/mm.h             |   2 +
 include/linux/pagemap.h        |   3 +
 include/linux/pmem.h           |  22 ++++++-
 include/linux/radix-tree.h     |   8 +++
 include/linux/rmap.h           |   5 ++
 mm/filemap.c                   |  71 ++++++++++++++++++++-
 mm/huge_memory.c               |  14 ++---
 mm/memory.c                    |  38 ++++++++---
 mm/rmap.c                      |  51 +++++++++++++++
 mm/truncate.c                  |  62 ++++++++++--------
 22 files changed, 425 insertions(+), 69 deletions(-)

-- 
2.1.0

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#1269364 — [PATCH v2 09/11] ext2: add support for DAX fsync/msync

To properly support the new DAX fsync/msync infrastructure filesystems
need to call dax_pfn_mkwrite() so that DAX can properly track when a user
write faults on a previously cleaned address.  They also need to call
dax_fsync() in the filesystem fsync() path.  This dax_fsync() call uses
addresses retrieved from get_block() so it needs to be ordered with
respect to truncate.  This is accomplished by using the same locking that
was set up for DAX page faults.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
---
 fs/ext2/file.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/fs/ext2/file.c b/fs/ext2/file.c
index 11a42c5..6c30ea2 100644
--- a/fs/ext2/file.c
+++ b/fs/ext2/file.c
@@ -102,8 +102,8 @@ static int ext2_dax_pfn_mkwrite(struct vm_area_struct *vma,
 {
 	struct inode *inode = file_inode(vma->vm_file);
 	struct ext2_inode_info *ei = EXT2_I(inode);
-	int ret = VM_FAULT_NOPAGE;
 	loff_t size;
+	int ret;
 
 	sb_start_pagefault(inode->i_sb);
 	file_update_time(vma->vm_file);
@@ -113,6 +113,8 @@ static int ext2_dax_pfn_mkwrite(struct vm_area_struct *vma,
 	size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
 	if (vmf->pgoff >= size)
 		ret = VM_FAULT_SIGBUS;
+	else
+		ret = dax_pfn_mkwrite(vma, vmf);
 
 	up_read(&ei->dax_sem);
 	sb_end_pagefault(inode->i_sb);
@@ -161,6 +163,16 @@ int ext2_fsync(struct file *file, loff_t start, loff_t end, int datasync)
 	struct super_block *sb = file->f_mapping->host->i_sb;
 	struct address_space *mapping = sb->s_bdev->bd_inode->i_mapping;
 
+#ifdef CONFIG_FS_DAX
+	if (dax_mapping(mapping)) {
+		struct ext2_inode_info *ei = EXT2_I(file_inode(file));
+
+		down_read(&ei->dax_sem);
+		dax_fsync(mapping, start, end);
+		up_read(&ei->dax_sem);
+	}
+#endif
+
 	ret = generic_file_fsync(file, start, end, datasync);
 	if (ret == -EIO || test_and_clear_bit(AS_EIO, &mapping->flags)) {
 		/* We don't really know where the IO error happened... */
-- 
2.1.0

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#1269365 — [PATCH v2 07/11] mm: add find_get_entries_tag()

Add find_get_entries_tag() to the family of functions that include
find_get_entries(), find_get_pages() and find_get_pages_tag().  This is
needed for DAX dirty page handling because we need a list of both page
offsets and radix tree entries ('indices' and 'entries' in this function)
that are marked with the PAGECACHE_TAG_TOWRITE tag.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
---
 include/linux/pagemap.h |  3 +++
 mm/filemap.c            | 61 +++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 64 insertions(+)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index a6c78e0..6fea3be 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -354,6 +354,9 @@ unsigned find_get_pages_contig(struct address_space *mapping, pgoff_t start,
 			       unsigned int nr_pages, struct page **pages);
 unsigned find_get_pages_tag(struct address_space *mapping, pgoff_t *index,
 			int tag, unsigned int nr_pages, struct page **pages);
+unsigned find_get_entries_tag(struct address_space *mapping, pgoff_t start,
+			int tag, unsigned int nr_entries,
+			struct page **entries, pgoff_t *indices);
 
 struct page *grab_cache_page_write_begin(struct address_space *mapping,
 			pgoff_t index, unsigned flags);
diff --git a/mm/filemap.c b/mm/filemap.c
index d5e94fd..89ab448 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1454,6 +1454,67 @@ repeat:
 }
 EXPORT_SYMBOL(find_get_pages_tag);
 
+/**
+ * find_get_entries_tag - find and return entries that match @tag
+ * @mapping:	the address_space to search
+ * @start:	the starting page cache index
+ * @tag:	the tag index
+ * @nr_entries:	the maximum number of entries
+ * @entries:	where the resulting entries are placed
+ * @indices:	the cache indices corresponding to the entries in @entries
+ *
+ * Like find_get_entries, except we only return entries which are tagged with
+ * @tag.
+ */
+unsigned find_get_entries_tag(struct address_space *mapping, pgoff_t start,
+			int tag, unsigned int nr_entries,
+			struct page **entries, pgoff_t *indices)
+{
+	void **slot;
+	unsigned int ret = 0;
+	struct radix_tree_iter iter;
+
+	if (!nr_entries)
+		return 0;
+
+	rcu_read_lock();
+restart:
+	radix_tree_for_each_tagged(slot, &mapping->page_tree,
+				   &iter, start, tag) {
+		struct page *page;
+repeat:
+		page = radix_tree_deref_slot(slot);
+		if (unlikely(!page))
+			continue;
+		if (radix_tree_exception(page)) {
+			if (radix_tree_deref_retry(page))
+				goto restart;
+			/*
+			 * A shadow entry of a recently evicted page, a swap
+			 * entry from shmem/tmpfs or a DAX entry.  Return it
+			 * without attempting to raise page count.
+			 */
+			goto export;
+		}
+		if (!page_cache_get_speculative(page))
+			goto repeat;
+
+		/* Has the page moved? */
+		if (unlikely(page != *slot)) {
+			page_cache_release(page);
+			goto repeat;
+		}
+export:
+		indices[ret] = iter.index;
+		entries[ret] = page;
+		if (++ret == nr_entries)
+			break;
+	}
+	rcu_read_unlock();
+	return ret;
+}
+EXPORT_SYMBOL(find_get_entries_tag);
+
 /*
  * CD/DVDs are error prone. When a medium error occurs, the driver may fail
  * a _large_ part of the i/o request. Imagine the worst scenario:
-- 
2.1.0

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#1270668 — Re: [PATCH v2 07/11] mm: add find_get_entries_tag()

On Fri, Nov 13, 2015 at 05:06:46PM -0700, Ross Zwisler wrote:
> Add find_get_entries_tag() to the family of functions that include
> find_get_entries(), find_get_pages() and find_get_pages_tag().  This is
> needed for DAX dirty page handling because we need a list of both page
> offsets and radix tree entries ('indices' and 'entries' in this function)
> that are marked with the PAGECACHE_TAG_TOWRITE tag.
> 
> Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
> ---
>  include/linux/pagemap.h |  3 +++
>  mm/filemap.c            | 61 +++++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 64 insertions(+)
> 
> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> index a6c78e0..6fea3be 100644
> --- a/include/linux/pagemap.h
> +++ b/include/linux/pagemap.h
> @@ -354,6 +354,9 @@ unsigned find_get_pages_contig(struct address_space *mapping, pgoff_t start,
>  			       unsigned int nr_pages, struct page **pages);
>  unsigned find_get_pages_tag(struct address_space *mapping, pgoff_t *index,
>  			int tag, unsigned int nr_pages, struct page **pages);
> +unsigned find_get_entries_tag(struct address_space *mapping, pgoff_t start,
> +			int tag, unsigned int nr_entries,
> +			struct page **entries, pgoff_t *indices);
>  
>  struct page *grab_cache_page_write_begin(struct address_space *mapping,
>  			pgoff_t index, unsigned flags);
> diff --git a/mm/filemap.c b/mm/filemap.c
> index d5e94fd..89ab448 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -1454,6 +1454,67 @@ repeat:
>  }
>  EXPORT_SYMBOL(find_get_pages_tag);
>  
> +/**
> + * find_get_entries_tag - find and return entries that match @tag
> + * @mapping:	the address_space to search
> + * @start:	the starting page cache index
> + * @tag:	the tag index
> + * @nr_entries:	the maximum number of entries
> + * @entries:	where the resulting entries are placed
> + * @indices:	the cache indices corresponding to the entries in @entries
> + *
> + * Like find_get_entries, except we only return entries which are tagged with
> + * @tag.
> + */
> +unsigned find_get_entries_tag(struct address_space *mapping, pgoff_t start,
> +			int tag, unsigned int nr_entries,
> +			struct page **entries, pgoff_t *indices)
> +{
> +	void **slot;
> +	unsigned int ret = 0;
> +	struct radix_tree_iter iter;
> +
> +	if (!nr_entries)
> +		return 0;
> +
> +	rcu_read_lock();
> +restart:
> +	radix_tree_for_each_tagged(slot, &mapping->page_tree,
> +				   &iter, start, tag) {
> +		struct page *page;
> +repeat:
> +		page = radix_tree_deref_slot(slot);
> +		if (unlikely(!page))
> +			continue;
> +		if (radix_tree_exception(page)) {
> +			if (radix_tree_deref_retry(page))
> +				goto restart;

That restart condition looks wrong. ret can be non-zero, but we
start looking from the original start index again, resulting in
duplicates being added to the return arrays...

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com
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#1271518 — Re: [PATCH v2 07/11] mm: add find_get_entries_tag()

On Tue, Nov 17, 2015 at 09:42:22AM +1100, Dave Chinner wrote:
> On Fri, Nov 13, 2015 at 05:06:46PM -0700, Ross Zwisler wrote:
> > Add find_get_entries_tag() to the family of functions that include
> > find_get_entries(), find_get_pages() and find_get_pages_tag().  This is
> > needed for DAX dirty page handling because we need a list of both page
> > offsets and radix tree entries ('indices' and 'entries' in this function)
> > that are marked with the PAGECACHE_TAG_TOWRITE tag.
> > 
> > Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
> > ---
> >  include/linux/pagemap.h |  3 +++
> >  mm/filemap.c            | 61 +++++++++++++++++++++++++++++++++++++++++++++++++
> >  2 files changed, 64 insertions(+)
> > 
> > diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> > index a6c78e0..6fea3be 100644
> > --- a/include/linux/pagemap.h
> > +++ b/include/linux/pagemap.h
> > @@ -354,6 +354,9 @@ unsigned find_get_pages_contig(struct address_space *mapping, pgoff_t start,
> >  			       unsigned int nr_pages, struct page **pages);
> >  unsigned find_get_pages_tag(struct address_space *mapping, pgoff_t *index,
> >  			int tag, unsigned int nr_pages, struct page **pages);
> > +unsigned find_get_entries_tag(struct address_space *mapping, pgoff_t start,
> > +			int tag, unsigned int nr_entries,
> > +			struct page **entries, pgoff_t *indices);
> >  
> >  struct page *grab_cache_page_write_begin(struct address_space *mapping,
> >  			pgoff_t index, unsigned flags);
> > diff --git a/mm/filemap.c b/mm/filemap.c
> > index d5e94fd..89ab448 100644
> > --- a/mm/filemap.c
> > +++ b/mm/filemap.c
> > @@ -1454,6 +1454,67 @@ repeat:
> >  }
> >  EXPORT_SYMBOL(find_get_pages_tag);
> >  
> > +/**
> > + * find_get_entries_tag - find and return entries that match @tag
> > + * @mapping:	the address_space to search
> > + * @start:	the starting page cache index
> > + * @tag:	the tag index
> > + * @nr_entries:	the maximum number of entries
> > + * @entries:	where the resulting entries are placed
> > + * @indices:	the cache indices corresponding to the entries in @entries
> > + *
> > + * Like find_get_entries, except we only return entries which are tagged with
> > + * @tag.
> > + */
> > +unsigned find_get_entries_tag(struct address_space *mapping, pgoff_t start,
> > +			int tag, unsigned int nr_entries,
> > +			struct page **entries, pgoff_t *indices)
> > +{
> > +	void **slot;
> > +	unsigned int ret = 0;
> > +	struct radix_tree_iter iter;
> > +
> > +	if (!nr_entries)
> > +		return 0;
> > +
> > +	rcu_read_lock();
> > +restart:
> > +	radix_tree_for_each_tagged(slot, &mapping->page_tree,
> > +				   &iter, start, tag) {
> > +		struct page *page;
> > +repeat:
> > +		page = radix_tree_deref_slot(slot);
> > +		if (unlikely(!page))
> > +			continue;
> > +		if (radix_tree_exception(page)) {
> > +			if (radix_tree_deref_retry(page))
> > +				goto restart;
> 
> That restart condition looks wrong. ret can be non-zero, but we
> start looking from the original start index again, resulting in
> duplicates being added to the return arrays...

This same restart logic is used in all the functions in this family:
find_get_entry() (though the tag is "repeat"), find_get_entries(),
find_get_pages(), find_get_pages_contig() and find_get_pages_tag().

Most don't have it well commented, but there is a good comment in
find_get_pages():

	if (radix_tree_exception(page)) {                               
		if (radix_tree_deref_retry(page)) {                     
			/*                                              
			 * Transient condition which can only trigger   
			 * when entry at index 0 moves out of or back   
			 * to root: none yet gotten, safe to restart.   
			 */                                             
			WARN_ON(iter.index);                            
			goto restart;                                   
		}   

I think the logic is correct, but I'm happy to add this comment in
find_get_entries_tag() if it would make things clearer.
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#1269366 — [PATCH v2 10/11] ext4: add support for DAX fsync/msync

To properly support the new DAX fsync/msync infrastructure filesystems
need to call dax_pfn_mkwrite() so that DAX can properly track when a user
write faults on a previously cleaned address.  They also need to call
dax_fsync() in the filesystem fsync() path.  This dax_fsync() call uses
addresses retrieved from get_block() so it needs to be ordered with
respect to truncate.  This is accomplished by using the same locking that
was set up for DAX page faults.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
---
 fs/ext4/file.c  |  4 +++-
 fs/ext4/fsync.c | 12 ++++++++++--
 2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index 749b222..8c8965c 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -291,8 +291,8 @@ static int ext4_dax_pfn_mkwrite(struct vm_area_struct *vma,
 {
 	struct inode *inode = file_inode(vma->vm_file);
 	struct super_block *sb = inode->i_sb;
-	int ret = VM_FAULT_NOPAGE;
 	loff_t size;
+	int ret;
 
 	sb_start_pagefault(sb);
 	file_update_time(vma->vm_file);
@@ -300,6 +300,8 @@ static int ext4_dax_pfn_mkwrite(struct vm_area_struct *vma,
 	size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
 	if (vmf->pgoff >= size)
 		ret = VM_FAULT_SIGBUS;
+	else
+		ret = dax_pfn_mkwrite(vma, vmf);
 	up_read(&EXT4_I(inode)->i_mmap_sem);
 	sb_end_pagefault(sb);
 
diff --git a/fs/ext4/fsync.c b/fs/ext4/fsync.c
index 8850254..e87c29b 100644
--- a/fs/ext4/fsync.c
+++ b/fs/ext4/fsync.c
@@ -27,6 +27,7 @@
 #include <linux/sched.h>
 #include <linux/writeback.h>
 #include <linux/blkdev.h>
+#include <linux/dax.h>
 
 #include "ext4.h"
 #include "ext4_jbd2.h"
@@ -86,7 +87,8 @@ static int ext4_sync_parent(struct inode *inode)
 
 int ext4_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
 {
-	struct inode *inode = file->f_mapping->host;
+	struct address_space *mapping = file->f_mapping;
+	struct inode *inode = mapping->host;
 	struct ext4_inode_info *ei = EXT4_I(inode);
 	journal_t *journal = EXT4_SB(inode->i_sb)->s_journal;
 	int ret = 0, err;
@@ -112,7 +114,13 @@ int ext4_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
 		goto out;
 	}
 
-	ret = filemap_write_and_wait_range(inode->i_mapping, start, end);
+	if (dax_mapping(mapping)) {
+		down_read(&ei->i_mmap_sem);
+		dax_fsync(mapping, start, end);
+		up_read(&ei->i_mmap_sem);
+	}
+
+	ret = filemap_write_and_wait_range(mapping, start, end);
 	if (ret)
 		return ret;
 	/*
-- 
2.1.0

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#1269368 — [PATCH v2 11/11] xfs: add support for DAX fsync/msync

To properly support the new DAX fsync/msync infrastructure filesystems
need to call dax_pfn_mkwrite() so that DAX can properly track when a user
write faults on a previously cleaned address.  They also need to call
dax_fsync() in the filesystem fsync() path.  This dax_fsync() call uses
addresses retrieved from get_block() so it needs to be ordered with
respect to truncate.  This is accomplished by using the same locking that
was set up for DAX page faults.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
---
 fs/xfs/xfs_file.c | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 39743ef..2b490a1 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -209,7 +209,8 @@ xfs_file_fsync(
 	loff_t			end,
 	int			datasync)
 {
-	struct inode		*inode = file->f_mapping->host;
+	struct address_space	*mapping = file->f_mapping;
+	struct inode		*inode = mapping->host;
 	struct xfs_inode	*ip = XFS_I(inode);
 	struct xfs_mount	*mp = ip->i_mount;
 	int			error = 0;
@@ -218,7 +219,13 @@ xfs_file_fsync(
 
 	trace_xfs_file_fsync(ip);
 
-	error = filemap_write_and_wait_range(inode->i_mapping, start, end);
+	if (dax_mapping(mapping)) {
+		xfs_ilock(XFS_I(inode), XFS_MMAPLOCK_SHARED);
+		dax_fsync(mapping, start, end);
+		xfs_iunlock(XFS_I(inode), XFS_MMAPLOCK_SHARED);
+	}
+
+	error = filemap_write_and_wait_range(mapping, start, end);
 	if (error)
 		return error;
 
@@ -1603,9 +1610,8 @@ xfs_filemap_pmd_fault(
 /*
  * pfn_mkwrite was originally inteneded to ensure we capture time stamp
  * updates on write faults. In reality, it's need to serialise against
- * truncate similar to page_mkwrite. Hence we open-code dax_pfn_mkwrite()
- * here and cycle the XFS_MMAPLOCK_SHARED to ensure we serialise the fault
- * barrier in place.
+ * truncate similar to page_mkwrite. Hence we cycle the XFS_MMAPLOCK_SHARED
+ * to ensure we serialise the fault barrier in place.
  */
 static int
 xfs_filemap_pfn_mkwrite(
@@ -1628,6 +1634,8 @@ xfs_filemap_pfn_mkwrite(
 	size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
 	if (vmf->pgoff >= size)
 		ret = VM_FAULT_SIGBUS;
+	else if (IS_DAX(inode))
+		ret = dax_pfn_mkwrite(vma, vmf);
 	xfs_iunlock(ip, XFS_MMAPLOCK_SHARED);
 	sb_end_pagefault(inode->i_sb);
 	return ret;
-- 
2.1.0

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#1270685 — Re: [PATCH v2 11/11] xfs: add support for DAX fsync/msync

On Fri, Nov 13, 2015 at 05:06:50PM -0700, Ross Zwisler wrote:
> To properly support the new DAX fsync/msync infrastructure filesystems
> need to call dax_pfn_mkwrite() so that DAX can properly track when a user
> write faults on a previously cleaned address.  They also need to call
> dax_fsync() in the filesystem fsync() path.  This dax_fsync() call uses
> addresses retrieved from get_block() so it needs to be ordered with
> respect to truncate.  This is accomplished by using the same locking that
> was set up for DAX page faults.
> 
> Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
> ---
>  fs/xfs/xfs_file.c | 18 +++++++++++++-----
>  1 file changed, 13 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> index 39743ef..2b490a1 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -209,7 +209,8 @@ xfs_file_fsync(
>  	loff_t			end,
>  	int			datasync)
>  {
> -	struct inode		*inode = file->f_mapping->host;
> +	struct address_space	*mapping = file->f_mapping;
> +	struct inode		*inode = mapping->host;
>  	struct xfs_inode	*ip = XFS_I(inode);
>  	struct xfs_mount	*mp = ip->i_mount;
>  	int			error = 0;
> @@ -218,7 +219,13 @@ xfs_file_fsync(
>  
>  	trace_xfs_file_fsync(ip);
>  
> -	error = filemap_write_and_wait_range(inode->i_mapping, start, end);
> +	if (dax_mapping(mapping)) {
> +		xfs_ilock(XFS_I(inode), XFS_MMAPLOCK_SHARED);
> +		dax_fsync(mapping, start, end);
> +		xfs_iunlock(XFS_I(inode), XFS_MMAPLOCK_SHARED);
> +	}
> +
> +	error = filemap_write_and_wait_range(mapping, start, end);

Ok, I don't understand a couple of things here.

Firstly, if it's a DAX mapping, why are we still calling
filemap_write_and_wait_range() after the dax_fsync() call that has
already written back all the dirty cachelines?

Secondly, exactly what is the XFS_MMAPLOCK_SHARED lock supposed to
be doing here? I don't see where dax_fsync() has any callouts to
get_block(), so the comment "needs to be ordered with respect to
truncate" doesn't make any obvious sense. If we have a racing
truncate removing entries from the radix tree, then thanks to the
mapping tree lock we'll either find an entry we need to write back,
or we won't find any entry at all, right?

Lastly, this flushing really needs to be inside
filemap_write_and_wait_range(), because we call the writeback code
from many more places than just fsync to ensure ordering of various
operations such that files are in known state before proceeding
(e.g. hole punch).

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com
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#1271579 — Re: [PATCH v2 11/11] xfs: add support for DAX fsync/msync

On Tue, Nov 17, 2015 at 10:12:22AM +1100, Dave Chinner wrote:
> On Fri, Nov 13, 2015 at 05:06:50PM -0700, Ross Zwisler wrote:
> > To properly support the new DAX fsync/msync infrastructure filesystems
> > need to call dax_pfn_mkwrite() so that DAX can properly track when a user
> > write faults on a previously cleaned address.  They also need to call
> > dax_fsync() in the filesystem fsync() path.  This dax_fsync() call uses
> > addresses retrieved from get_block() so it needs to be ordered with
> > respect to truncate.  This is accomplished by using the same locking that
> > was set up for DAX page faults.
> > 
> > Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
> > ---
> >  fs/xfs/xfs_file.c | 18 +++++++++++++-----
> >  1 file changed, 13 insertions(+), 5 deletions(-)
> > 
> > diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> > index 39743ef..2b490a1 100644
> > --- a/fs/xfs/xfs_file.c
> > +++ b/fs/xfs/xfs_file.c
> > @@ -209,7 +209,8 @@ xfs_file_fsync(
> >  	loff_t			end,
> >  	int			datasync)
> >  {
> > -	struct inode		*inode = file->f_mapping->host;
> > +	struct address_space	*mapping = file->f_mapping;
> > +	struct inode		*inode = mapping->host;
> >  	struct xfs_inode	*ip = XFS_I(inode);
> >  	struct xfs_mount	*mp = ip->i_mount;
> >  	int			error = 0;
> > @@ -218,7 +219,13 @@ xfs_file_fsync(
> >  
> >  	trace_xfs_file_fsync(ip);
> >  
> > -	error = filemap_write_and_wait_range(inode->i_mapping, start, end);
> > +	if (dax_mapping(mapping)) {
> > +		xfs_ilock(XFS_I(inode), XFS_MMAPLOCK_SHARED);
> > +		dax_fsync(mapping, start, end);
> > +		xfs_iunlock(XFS_I(inode), XFS_MMAPLOCK_SHARED);
> > +	}
> > +
> > +	error = filemap_write_and_wait_range(mapping, start, end);
> 
> Ok, I don't understand a couple of things here.
> 
> Firstly, if it's a DAX mapping, why are we still calling
> filemap_write_and_wait_range() after the dax_fsync() call that has
> already written back all the dirty cachelines?
> 
> Secondly, exactly what is the XFS_MMAPLOCK_SHARED lock supposed to
> be doing here? I don't see where dax_fsync() has any callouts to
> get_block(), so the comment "needs to be ordered with respect to
> truncate" doesn't make any obvious sense. If we have a racing
> truncate removing entries from the radix tree, then thanks to the
> mapping tree lock we'll either find an entry we need to write back,
> or we won't find any entry at all, right?

You're right, dax_fsync() doesn't call out to get_block() any more.  It does
save the results of get_block() calls from the page faults, though, and I was
concerned about the following race:

fsync thread				truncate thread
------------				---------------
dax_fsync()
save tagged entries in pvec

					change block mapping for inode so that
					entries saved in pvec are no longer
					owned by this inode

loop through pvec using stale results
from get_block(), flushing and cleaning
entries we no longer own

In looking at the xfs_file_fsync() code, though, it seems like if this race
existed it would also exist for page cache entries that were being put into a
pvec in write_cache_pages(), and that we would similarly be writing back
cached pages that no longer belong to this inode.

Is this race non-existent?

> Lastly, this flushing really needs to be inside
> filemap_write_and_wait_range(), because we call the writeback code
> from many more places than just fsync to ensure ordering of various
> operations such that files are in known state before proceeding
> (e.g. hole punch).

The call to dax_fsync() (soon to be dax_writeback_mapping_range()) first lived
in do_writepages() in the RFC version, but was moved into the filesystem so we
could have access to get_block(), which is no longer needed, and so we could
use the FS level locking.  If the race described above isn't an issue then I
agree moving this call out of the filesystems and down into the generic page
writeback code is probably the right thing to do.

Thanks for the feedback.
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#1273643 — Re: [PATCH v2 11/11] xfs: add support for DAX fsync/msync

On Tue, Nov 17, 2015 at 12:03:41PM -0700, Ross Zwisler wrote:
> On Tue, Nov 17, 2015 at 10:12:22AM +1100, Dave Chinner wrote:
> > On Fri, Nov 13, 2015 at 05:06:50PM -0700, Ross Zwisler wrote:
> > > To properly support the new DAX fsync/msync infrastructure filesystems
> > > need to call dax_pfn_mkwrite() so that DAX can properly track when a user
> > > write faults on a previously cleaned address.  They also need to call
> > > dax_fsync() in the filesystem fsync() path.  This dax_fsync() call uses
> > > addresses retrieved from get_block() so it needs to be ordered with
> > > respect to truncate.  This is accomplished by using the same locking that
> > > was set up for DAX page faults.
> > > 
> > > Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
> > > ---
> > >  fs/xfs/xfs_file.c | 18 +++++++++++++-----
> > >  1 file changed, 13 insertions(+), 5 deletions(-)
> > > 
> > > diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> > > index 39743ef..2b490a1 100644
> > > --- a/fs/xfs/xfs_file.c
> > > +++ b/fs/xfs/xfs_file.c
> > > @@ -209,7 +209,8 @@ xfs_file_fsync(
> > >  	loff_t			end,
> > >  	int			datasync)
> > >  {
> > > -	struct inode		*inode = file->f_mapping->host;
> > > +	struct address_space	*mapping = file->f_mapping;
> > > +	struct inode		*inode = mapping->host;
> > >  	struct xfs_inode	*ip = XFS_I(inode);
> > >  	struct xfs_mount	*mp = ip->i_mount;
> > >  	int			error = 0;
> > > @@ -218,7 +219,13 @@ xfs_file_fsync(
> > >  
> > >  	trace_xfs_file_fsync(ip);
> > >  
> > > -	error = filemap_write_and_wait_range(inode->i_mapping, start, end);
> > > +	if (dax_mapping(mapping)) {
> > > +		xfs_ilock(XFS_I(inode), XFS_MMAPLOCK_SHARED);
> > > +		dax_fsync(mapping, start, end);
> > > +		xfs_iunlock(XFS_I(inode), XFS_MMAPLOCK_SHARED);
> > > +	}
> > > +
> > > +	error = filemap_write_and_wait_range(mapping, start, end);
> > 
> > Ok, I don't understand a couple of things here.
> > 
> > Firstly, if it's a DAX mapping, why are we still calling
> > filemap_write_and_wait_range() after the dax_fsync() call that has
> > already written back all the dirty cachelines?
> > 
> > Secondly, exactly what is the XFS_MMAPLOCK_SHARED lock supposed to
> > be doing here? I don't see where dax_fsync() has any callouts to
> > get_block(), so the comment "needs to be ordered with respect to
> > truncate" doesn't make any obvious sense. If we have a racing
> > truncate removing entries from the radix tree, then thanks to the
> > mapping tree lock we'll either find an entry we need to write back,
> > or we won't find any entry at all, right?
> 
> You're right, dax_fsync() doesn't call out to get_block() any more.  It does
> save the results of get_block() calls from the page faults, though, and I was
> concerned about the following race:
> 
> fsync thread				truncate thread
> ------------				---------------
> dax_fsync()
> save tagged entries in pvec
> 
> 					change block mapping for inode so that
> 					entries saved in pvec are no longer
> 					owned by this inode
> 
> loop through pvec using stale results
> from get_block(), flushing and cleaning
> entries we no longer own

dax_fsync is trying to do lockless lookups on an object that has no
internal reference count or synchronisation mechanism. That simply
doesn't work. In contrast, the struct page has the page lock, and
then with that held we can do the page->mapping checks to serialise
against and detect races with invalidation.

If you note the code in clear_exceptional_entry() in the
invalidation code:

        spin_lock_irq(&mapping->tree_lock);
        /*
         * Regular page slots are stabilized by the page lock even
         * without the tree itself locked.  These unlocked entries
         * need verification under the tree lock.
         */
        if (!__radix_tree_lookup(&mapping->page_tree, index, &node, &slot))
                goto unlock;
        if (*slot != entry)
		goto unlock;
	radix_tree_replace_slot(slot, NULL);


it basically says exactly this: exception entries are only valid
when the lookup is done under the mapping tree lock. IOWs, while you
can find exceptional entries via lockless radix tree lookups, you
*can't use them* safely.

Hence dax_fsync() needs to validate the exceptional entries it finds
via the pvec lookup under the mapping tree lock, and then flush the
cache while still holding the mapping tree lock. At that point, it
is safe against invalidation races....

> In looking at the xfs_file_fsync() code, though, it seems like if this race
> existed it would also exist for page cache entries that were being put into a
> pvec in write_cache_pages(), and that we would similarly be writing back
> cached pages that no longer belong to this inode.

That's what the page->mapping checks in write_cache_pages() protect
against. Everywhere you see a "lock_page(); if (page->mapping !=
mapping)" style of operation, it is checking against a racing
page invalidation.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com
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#1269369 — [PATCH v2 05/11] mm: add follow_pte_pmd()

Similar to follow_pte(), follow_pte_pmd() allows either a PTE leaf or a
huge page PMD leaf to be found and returned.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Suggested-by: Dave Hansen <dave.hansen@linux.intel.com>
---
 include/linux/mm.h |  2 ++
 mm/memory.c        | 38 ++++++++++++++++++++++++++++++--------
 2 files changed, 32 insertions(+), 8 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 80001de..393441c 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1166,6 +1166,8 @@ int copy_page_range(struct mm_struct *dst, struct mm_struct *src,
 			struct vm_area_struct *vma);
 void unmap_mapping_range(struct address_space *mapping,
 		loff_t const holebegin, loff_t const holelen, int even_cows);
+int follow_pte_pmd(struct mm_struct *mm, unsigned long address,
+			     pte_t **ptepp, pmd_t **pmdpp, spinlock_t **ptlp);
 int follow_pfn(struct vm_area_struct *vma, unsigned long address,
 	unsigned long *pfn);
 int follow_phys(struct vm_area_struct *vma, unsigned long address,
diff --git a/mm/memory.c b/mm/memory.c
index deb679c..7f4090e 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3512,8 +3512,8 @@ int __pmd_alloc(struct mm_struct *mm, pud_t *pud, unsigned long address)
 }
 #endif /* __PAGETABLE_PMD_FOLDED */
 
-static int __follow_pte(struct mm_struct *mm, unsigned long address,
-		pte_t **ptepp, spinlock_t **ptlp)
+static int __follow_pte_pmd(struct mm_struct *mm, unsigned long address,
+		pte_t **ptepp, pmd_t **pmdpp, spinlock_t **ptlp)
 {
 	pgd_t *pgd;
 	pud_t *pud;
@@ -3529,12 +3529,20 @@ static int __follow_pte(struct mm_struct *mm, unsigned long address,
 		goto out;
 
 	pmd = pmd_offset(pud, address);
-	VM_BUG_ON(pmd_trans_huge(*pmd));
-	if (pmd_none(*pmd) || unlikely(pmd_bad(*pmd)))
-		goto out;
 
-	/* We cannot handle huge page PFN maps. Luckily they don't exist. */
-	if (pmd_huge(*pmd))
+	if (pmd_huge(*pmd)) {
+		if (!pmdpp)
+			goto out;
+
+		*ptlp = pmd_lock(mm, pmd);
+		if (pmd_huge(*pmd)) {
+			*pmdpp = pmd;
+			return 0;
+		}
+		spin_unlock(*ptlp);
+	}
+
+	if (pmd_none(*pmd) || unlikely(pmd_bad(*pmd)))
 		goto out;
 
 	ptep = pte_offset_map_lock(mm, pmd, address, ptlp);
@@ -3557,9 +3565,23 @@ static inline int follow_pte(struct mm_struct *mm, unsigned long address,
 
 	/* (void) is needed to make gcc happy */
 	(void) __cond_lock(*ptlp,
-			   !(res = __follow_pte(mm, address, ptepp, ptlp)));
+			   !(res = __follow_pte_pmd(mm, address, ptepp, NULL,
+					   ptlp)));
+	return res;
+}
+
+int follow_pte_pmd(struct mm_struct *mm, unsigned long address,
+			     pte_t **ptepp, pmd_t **pmdpp, spinlock_t **ptlp)
+{
+	int res;
+
+	/* (void) is needed to make gcc happy */
+	(void) __cond_lock(*ptlp,
+			   !(res = __follow_pte_pmd(mm, address, ptepp, pmdpp,
+					   ptlp)));
 	return res;
 }
+EXPORT_SYMBOL(follow_pte_pmd);
 
 /**
  * follow_pfn - look up PFN at a user virtual address
-- 
2.1.0

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#1269370 — [PATCH v2 01/11] pmem: add wb_cache_pmem() to the PMEM API

The function __arch_wb_cache_pmem() was already an internal implementation
detail of the x86 PMEM API, but this functionality needs to be exported as
part of the general PMEM API to handle the fsync/msync case for DAX mmaps.

One thing worth noting is that we really do want this to be part of the
PMEM API as opposed to a stand-alone function like clflush_cache_range()
because of ordering restrictions.  By having wb_cache_pmem() as part of the
PMEM API we can leave it unordered, call it multiple times to write back
large amounts of memory, and then order the multiple calls with a single
wmb_pmem().

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
---
 arch/x86/include/asm/pmem.h | 11 ++++++-----
 include/linux/pmem.h        | 22 +++++++++++++++++++++-
 2 files changed, 27 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/pmem.h b/arch/x86/include/asm/pmem.h
index d8ce3ec..6c7ade0 100644
--- a/arch/x86/include/asm/pmem.h
+++ b/arch/x86/include/asm/pmem.h
@@ -67,18 +67,19 @@ static inline void arch_wmb_pmem(void)
 }
 
 /**
- * __arch_wb_cache_pmem - write back a cache range with CLWB
+ * arch_wb_cache_pmem - write back a cache range with CLWB
  * @vaddr:	virtual start address
  * @size:	number of bytes to write back
  *
  * Write back a cache range using the CLWB (cache line write back)
  * instruction.  This function requires explicit ordering with an
- * arch_wmb_pmem() call.  This API is internal to the x86 PMEM implementation.
+ * arch_wmb_pmem() call.
  */
-static inline void __arch_wb_cache_pmem(void *vaddr, size_t size)
+static inline void arch_wb_cache_pmem(void __pmem *addr, size_t size)
 {
 	u16 x86_clflush_size = boot_cpu_data.x86_clflush_size;
 	unsigned long clflush_mask = x86_clflush_size - 1;
+	void *vaddr = (void __force *)addr;
 	void *vend = vaddr + size;
 	void *p;
 
@@ -115,7 +116,7 @@ static inline size_t arch_copy_from_iter_pmem(void __pmem *addr, size_t bytes,
 	len = copy_from_iter_nocache(vaddr, bytes, i);
 
 	if (__iter_needs_pmem_wb(i))
-		__arch_wb_cache_pmem(vaddr, bytes);
+		arch_wb_cache_pmem(addr, bytes);
 
 	return len;
 }
@@ -138,7 +139,7 @@ static inline void arch_clear_pmem(void __pmem *addr, size_t size)
 	else
 		memset(vaddr, 0, size);
 
-	__arch_wb_cache_pmem(vaddr, size);
+	arch_wb_cache_pmem(addr, size);
 }
 
 static inline bool __arch_has_wmb_pmem(void)
diff --git a/include/linux/pmem.h b/include/linux/pmem.h
index 85f810b3..2cd5003 100644
--- a/include/linux/pmem.h
+++ b/include/linux/pmem.h
@@ -53,12 +53,18 @@ static inline void arch_clear_pmem(void __pmem *addr, size_t size)
 {
 	BUG();
 }
+
+static inline void arch_wb_cache_pmem(void __pmem *addr, size_t size)
+{
+	BUG();
+}
 #endif
 
 /*
  * Architectures that define ARCH_HAS_PMEM_API must provide
  * implementations for arch_memcpy_to_pmem(), arch_wmb_pmem(),
- * arch_copy_from_iter_pmem(), arch_clear_pmem() and arch_has_wmb_pmem().
+ * arch_copy_from_iter_pmem(), arch_clear_pmem(), arch_wb_cache_pmem()
+ * and arch_has_wmb_pmem().
  */
 static inline void memcpy_from_pmem(void *dst, void __pmem const *src, size_t size)
 {
@@ -202,4 +208,18 @@ static inline void clear_pmem(void __pmem *addr, size_t size)
 	else
 		default_clear_pmem(addr, size);
 }
+
+/**
+ * wb_cache_pmem - write back processor cache for PMEM memory range
+ * @addr:	virtual start address
+ * @size:	number of bytes to write back
+ *
+ * Write back the processor cache range starting at 'addr' for 'size' bytes.
+ * This function requires explicit ordering with a wmb_pmem() call.
+ */
+static inline void wb_cache_pmem(void __pmem *addr, size_t size)
+{
+	if (arch_has_pmem_api())
+		arch_wb_cache_pmem(addr, size);
+}
 #endif /* __PMEM_H__ */
-- 
2.1.0

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#1269371 — [PATCH v2 08/11] dax: add support for fsync/sync

To properly handle fsync/msync in an efficient way DAX needs to track dirty
pages so it is able to flush them durably to media on demand.

The tracking of dirty pages is done via the radix tree in struct
address_space.  This radix tree is already used by the page writeback
infrastructure for tracking dirty pages associated with an open file, and
it already has support for exceptional (non struct page*) entries.  We
build upon these features to add exceptional entries to the radix tree for
DAX dirty PMD or PTE pages at fault time.

When called as part of the msync/fsync flush path DAX queries the radix
tree for dirty entries, flushing them and then marking the PTE or PMD page
table entries as clean.  The step of cleaning the PTE or PMD entries is
necessary so that on subsequent writes to the same page we get a new write
fault allowing us to once again dirty the DAX tag in the radix tree.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
---
 fs/dax.c            | 140 +++++++++++++++++++++++++++++++++++++++++++++++++---
 include/linux/dax.h |   1 +
 mm/huge_memory.c    |  14 +++---
 3 files changed, 141 insertions(+), 14 deletions(-)

diff --git a/fs/dax.c b/fs/dax.c
index 131fd35a..9ce6d1b 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -24,7 +24,9 @@
 #include <linux/memcontrol.h>
 #include <linux/mm.h>
 #include <linux/mutex.h>
+#include <linux/pagevec.h>
 #include <linux/pmem.h>
+#include <linux/rmap.h>
 #include <linux/sched.h>
 #include <linux/uio.h>
 #include <linux/vmstat.h>
@@ -287,6 +289,53 @@ static int copy_user_bh(struct page *to, struct buffer_head *bh,
 	return 0;
 }
 
+static int dax_dirty_pgoff(struct address_space *mapping, unsigned long pgoff,
+		void __pmem *addr, bool pmd_entry)
+{
+	struct radix_tree_root *page_tree = &mapping->page_tree;
+	int error = 0;
+	void *entry;
+
+	__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
+
+	spin_lock_irq(&mapping->tree_lock);
+	entry = radix_tree_lookup(page_tree, pgoff);
+	if (addr == NULL) {
+		if (entry)
+			goto dirty;
+		else {
+			WARN(1, "DAX pfn_mkwrite failed to find an entry");
+			goto out;
+		}
+	}
+
+	if (entry) {
+		if (pmd_entry && RADIX_DAX_TYPE(entry) == RADIX_DAX_PTE) {
+			radix_tree_delete(&mapping->page_tree, pgoff);
+			mapping->nrdax--;
+		} else
+			goto dirty;
+	}
+
+	BUG_ON(RADIX_DAX_TYPE(addr));
+	if (pmd_entry)
+		error = radix_tree_insert(page_tree, pgoff,
+				RADIX_DAX_PMD_ENTRY(addr));
+	else
+		error = radix_tree_insert(page_tree, pgoff,
+				RADIX_DAX_PTE_ENTRY(addr));
+
+	if (error)
+		goto out;
+
+	mapping->nrdax++;
+ dirty:
+	radix_tree_tag_set(page_tree, pgoff, PAGECACHE_TAG_DIRTY);
+ out:
+	spin_unlock_irq(&mapping->tree_lock);
+	return error;
+}
+
 static int dax_insert_mapping(struct inode *inode, struct buffer_head *bh,
 			struct vm_area_struct *vma, struct vm_fault *vmf)
 {
@@ -327,7 +376,10 @@ static int dax_insert_mapping(struct inode *inode, struct buffer_head *bh,
 	}
 
 	error = vm_insert_mixed(vma, vaddr, pfn);
+	if (error)
+		goto out;
 
+	error = dax_dirty_pgoff(mapping, vmf->pgoff, addr, false);
  out:
 	i_mmap_unlock_read(mapping);
 
@@ -450,6 +502,7 @@ int __dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
 		delete_from_page_cache(page);
 		unlock_page(page);
 		page_cache_release(page);
+		page = NULL;
 	}
 
 	/*
@@ -537,7 +590,7 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
 	pgoff_t size, pgoff;
 	sector_t block, sector;
 	unsigned long pfn;
-	int result = 0;
+	int error, result = 0;
 
 	/* Fall back to PTEs if we're going to COW */
 	if (write && !(vma->vm_flags & VM_SHARED))
@@ -638,6 +691,10 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
 		}
 
 		result |= vmf_insert_pfn_pmd(vma, address, pmd, pfn, write);
+
+		error = dax_dirty_pgoff(mapping, pgoff, kaddr, true);
+		if (error)
+			goto fallback;
 	}
 
  out:
@@ -689,15 +746,12 @@ EXPORT_SYMBOL_GPL(dax_pmd_fault);
  * dax_pfn_mkwrite - handle first write to DAX page
  * @vma: The virtual memory area where the fault occurred
  * @vmf: The description of the fault
- *
  */
 int dax_pfn_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
 {
-	struct super_block *sb = file_inode(vma->vm_file)->i_sb;
+	struct file *file = vma->vm_file;
 
-	sb_start_pagefault(sb);
-	file_update_time(vma->vm_file);
-	sb_end_pagefault(sb);
+	dax_dirty_pgoff(file->f_mapping, vmf->pgoff, NULL, false);
 	return VM_FAULT_NOPAGE;
 }
 EXPORT_SYMBOL_GPL(dax_pfn_mkwrite);
@@ -772,3 +826,77 @@ int dax_truncate_page(struct inode *inode, loff_t from, get_block_t get_block)
 	return dax_zero_page_range(inode, from, length, get_block);
 }
 EXPORT_SYMBOL_GPL(dax_truncate_page);
+
+static void dax_sync_entry(struct address_space *mapping, pgoff_t pgoff,
+		void *entry)
+{
+	struct radix_tree_root *page_tree = &mapping->page_tree;
+	int type = RADIX_DAX_TYPE(entry);
+	size_t size;
+
+	BUG_ON(type != RADIX_DAX_PTE && type != RADIX_DAX_PMD);
+
+	spin_lock_irq(&mapping->tree_lock);
+	if (!radix_tree_tag_get(page_tree, pgoff, PAGECACHE_TAG_TOWRITE)) {
+		/* another fsync thread already wrote back this entry */
+		spin_unlock_irq(&mapping->tree_lock);
+		return;
+	}
+	radix_tree_tag_clear(page_tree, pgoff, PAGECACHE_TAG_TOWRITE);
+	radix_tree_tag_clear(page_tree, pgoff, PAGECACHE_TAG_DIRTY);
+	spin_unlock_irq(&mapping->tree_lock);
+
+	if (type == RADIX_DAX_PMD)
+		size = PMD_SIZE;
+	else
+		size = PAGE_SIZE;
+
+	wb_cache_pmem(RADIX_DAX_ADDR(entry), size);
+	pgoff_mkclean(pgoff, mapping);
+}
+
+/*
+ * Flush the mapping to the persistent domain within the byte range of (start,
+ * end). This is required by data integrity operations to ensure file data is on
+ * persistent storage prior to completion of the operation. It also requires us
+ * to clean the mappings (i.e. write -> RO) so that we'll get a new fault when
+ * the file is written to again so we have an indication that we need to flush
+ * the mapping if a data integrity operation takes place.
+ *
+ * We don't need commits to storage here - the filesystems will issue flushes
+ * appropriately at the conclusion of the data integrity operation via REQ_FUA
+ * writes or blkdev_issue_flush() commands.  This requires the DAX block device
+ * to implement persistent storage domain fencing/commits on receiving a
+ * REQ_FLUSH or REQ_FUA request so that this works as expected by the higher
+ * layers.
+ */
+void dax_fsync(struct address_space *mapping, loff_t start, loff_t end)
+{
+	struct inode *inode = mapping->host;
+	pgoff_t indices[PAGEVEC_SIZE];
+	struct pagevec pvec;
+	int i;
+
+	pgoff_t start_page = start >> PAGE_CACHE_SHIFT;
+	pgoff_t end_page = end >> PAGE_CACHE_SHIFT;
+
+	if (mapping->nrdax == 0)
+		return;
+
+	BUG_ON(inode->i_blkbits != PAGE_SHIFT);
+
+	tag_pages_for_writeback(mapping, start_page, end_page);
+
+	pagevec_init(&pvec, 0);
+	while (1) {
+		pvec.nr = find_get_entries_tag(mapping, start_page,
+				PAGECACHE_TAG_TOWRITE, PAGEVEC_SIZE,
+				pvec.pages, indices);
+
+		if (pvec.nr == 0)
+			break;
+
+		for (i = 0; i < pvec.nr; i++)
+			dax_sync_entry(mapping, indices[i], pvec.pages[i]);
+	}
+}
diff --git a/include/linux/dax.h b/include/linux/dax.h
index e9d57f68..2b3ce6f 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -41,4 +41,5 @@ static inline bool dax_mapping(struct address_space *mapping)
 {
 	return mapping->host && IS_DAX(mapping->host);
 }
+void dax_fsync(struct address_space *mapping, loff_t start, loff_t end);
 #endif
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index bbac913..1b3df56 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -877,15 +877,13 @@ static void insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
 	spinlock_t *ptl;
 
 	ptl = pmd_lock(mm, pmd);
-	if (pmd_none(*pmd)) {
-		entry = pmd_mkhuge(pfn_pmd(pfn, prot));
-		if (write) {
-			entry = pmd_mkyoung(pmd_mkdirty(entry));
-			entry = maybe_pmd_mkwrite(entry, vma);
-		}
-		set_pmd_at(mm, addr, pmd, entry);
-		update_mmu_cache_pmd(vma, addr, pmd);
+	entry = pmd_mkhuge(pfn_pmd(pfn, prot));
+	if (write) {
+		entry = pmd_mkyoung(pmd_mkdirty(entry));
+		entry = maybe_pmd_mkwrite(entry, vma);
 	}
+	set_pmd_at(mm, addr, pmd, entry);
+	update_mmu_cache_pmd(vma, addr, pmd);
 	spin_unlock(ptl);
 }
 
-- 
2.1.0

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#1270673 — Re: [PATCH v2 08/11] dax: add support for fsync/sync

On Fri, Nov 13, 2015 at 05:06:47PM -0700, Ross Zwisler wrote:
> To properly handle fsync/msync in an efficient way DAX needs to track dirty
> pages so it is able to flush them durably to media on demand.
> 
> The tracking of dirty pages is done via the radix tree in struct
> address_space.  This radix tree is already used by the page writeback
> infrastructure for tracking dirty pages associated with an open file, and
> it already has support for exceptional (non struct page*) entries.  We
> build upon these features to add exceptional entries to the radix tree for
> DAX dirty PMD or PTE pages at fault time.
> 
> When called as part of the msync/fsync flush path DAX queries the radix
> tree for dirty entries, flushing them and then marking the PTE or PMD page
> table entries as clean.  The step of cleaning the PTE or PMD entries is
> necessary so that on subsequent writes to the same page we get a new write
> fault allowing us to once again dirty the DAX tag in the radix tree.
> 
> Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
> ---
>  fs/dax.c            | 140 +++++++++++++++++++++++++++++++++++++++++++++++++---
>  include/linux/dax.h |   1 +
>  mm/huge_memory.c    |  14 +++---
>  3 files changed, 141 insertions(+), 14 deletions(-)
> 
> diff --git a/fs/dax.c b/fs/dax.c
> index 131fd35a..9ce6d1b 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -24,7 +24,9 @@
>  #include <linux/memcontrol.h>
>  #include <linux/mm.h>
>  #include <linux/mutex.h>
> +#include <linux/pagevec.h>
>  #include <linux/pmem.h>
> +#include <linux/rmap.h>
>  #include <linux/sched.h>
>  #include <linux/uio.h>
>  #include <linux/vmstat.h>
> @@ -287,6 +289,53 @@ static int copy_user_bh(struct page *to, struct buffer_head *bh,
>  	return 0;
>  }
>  
> +static int dax_dirty_pgoff(struct address_space *mapping, unsigned long pgoff,
> +		void __pmem *addr, bool pmd_entry)
> +{
> +	struct radix_tree_root *page_tree = &mapping->page_tree;
> +	int error = 0;
> +	void *entry;
> +
> +	__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
> +
> +	spin_lock_irq(&mapping->tree_lock);
> +	entry = radix_tree_lookup(page_tree, pgoff);
> +	if (addr == NULL) {
> +		if (entry)
> +			goto dirty;
> +		else {
> +			WARN(1, "DAX pfn_mkwrite failed to find an entry");
> +			goto out;
> +		}
> +	}
> +
> +	if (entry) {
> +		if (pmd_entry && RADIX_DAX_TYPE(entry) == RADIX_DAX_PTE) {
> +			radix_tree_delete(&mapping->page_tree, pgoff);
> +			mapping->nrdax--;
> +		} else
> +			goto dirty;
> +	}

Logic is pretty spagettied here. Perhaps:

	entry = radix_tree_lookup(page_tree, pgoff);
	if (entry) {
		if (!pmd_entry || RADIX_DAX_TYPE(entry) == RADIX_DAX_PMD))
			goto dirty;
		radix_tree_delete(&mapping->page_tree, pgoff);
		mapping->nrdax--;
	} else {
		WARN_ON(!addr);
		goto out_unlock;
	}
....

> +
> +	BUG_ON(RADIX_DAX_TYPE(addr));
> +	if (pmd_entry)
> +		error = radix_tree_insert(page_tree, pgoff,
> +				RADIX_DAX_PMD_ENTRY(addr));
> +	else
> +		error = radix_tree_insert(page_tree, pgoff,
> +				RADIX_DAX_PTE_ENTRY(addr));
> +
> +	if (error)
> +		goto out;
> +
> +	mapping->nrdax++;
> + dirty:
> +	radix_tree_tag_set(page_tree, pgoff, PAGECACHE_TAG_DIRTY);
> + out:
> +	spin_unlock_irq(&mapping->tree_lock);

label should be "out_unlock" rather "out" to indicate in the code
that we are jumping to the correct spot in the error stack...

> +			goto fallback;
>  	}
>  
>   out:
> @@ -689,15 +746,12 @@ EXPORT_SYMBOL_GPL(dax_pmd_fault);
>   * dax_pfn_mkwrite - handle first write to DAX page
>   * @vma: The virtual memory area where the fault occurred
>   * @vmf: The description of the fault
> - *
>   */
>  int dax_pfn_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
>  {
> -	struct super_block *sb = file_inode(vma->vm_file)->i_sb;
> +	struct file *file = vma->vm_file;
>  
> -	sb_start_pagefault(sb);
> -	file_update_time(vma->vm_file);
> -	sb_end_pagefault(sb);
> +	dax_dirty_pgoff(file->f_mapping, vmf->pgoff, NULL, false);
>  	return VM_FAULT_NOPAGE;

This seems wrong - it's dropping the freeze protection on fault, and
now the inode timestamp won't get updated, either.

>  }
>  EXPORT_SYMBOL_GPL(dax_pfn_mkwrite);
> @@ -772,3 +826,77 @@ int dax_truncate_page(struct inode *inode, loff_t from, get_block_t get_block)
>  	return dax_zero_page_range(inode, from, length, get_block);
>  }
>  EXPORT_SYMBOL_GPL(dax_truncate_page);
> +
> +static void dax_sync_entry(struct address_space *mapping, pgoff_t pgoff,
> +		void *entry)
> +{

dax_writeback_pgoff() seems like a more consistent name (consider
dax_dirty_pgoff), and that we are actually doing a writeback
operation, not a "sync" operation.

> +	struct radix_tree_root *page_tree = &mapping->page_tree;
> +	int type = RADIX_DAX_TYPE(entry);
> +	size_t size;
> +
> +	BUG_ON(type != RADIX_DAX_PTE && type != RADIX_DAX_PMD);
> +
> +	spin_lock_irq(&mapping->tree_lock);
> +	if (!radix_tree_tag_get(page_tree, pgoff, PAGECACHE_TAG_TOWRITE)) {
> +		/* another fsync thread already wrote back this entry */
> +		spin_unlock_irq(&mapping->tree_lock);
> +		return;
> +	}
> +	radix_tree_tag_clear(page_tree, pgoff, PAGECACHE_TAG_TOWRITE);
> +	radix_tree_tag_clear(page_tree, pgoff, PAGECACHE_TAG_DIRTY);
> +	spin_unlock_irq(&mapping->tree_lock);
> +
> +	if (type == RADIX_DAX_PMD)
> +		size = PMD_SIZE;
> +	else
> +		size = PAGE_SIZE;
> +
> +	wb_cache_pmem(RADIX_DAX_ADDR(entry), size);
> +	pgoff_mkclean(pgoff, mapping);

This looks racy w.r.t. another operation setting the radix tree
dirty tags. i.e. there is no locking to serialise marking the
vma/pte clean and another operation marking the radix tree dirty.

> +}
> +
> +/*
> + * Flush the mapping to the persistent domain within the byte range of (start,
> + * end). This is required by data integrity operations to ensure file data is on
> + * persistent storage prior to completion of the operation. It also requires us
> + * to clean the mappings (i.e. write -> RO) so that we'll get a new fault when
> + * the file is written to again so we have an indication that we need to flush
> + * the mapping if a data integrity operation takes place.
> + *
> + * We don't need commits to storage here - the filesystems will issue flushes
> + * appropriately at the conclusion of the data integrity operation via REQ_FUA
> + * writes or blkdev_issue_flush() commands.  This requires the DAX block device
> + * to implement persistent storage domain fencing/commits on receiving a
> + * REQ_FLUSH or REQ_FUA request so that this works as expected by the higher
> + * layers.
> + */
> +void dax_fsync(struct address_space *mapping, loff_t start, loff_t end)
> +{

dax_writeback_mapping_range()

Cheers,

Dave.

-- 
Dave Chinner
david@fromorbit.com
--
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#1271535 — Re: [PATCH v2 08/11] dax: add support for fsync/sync

On Tue, Nov 17, 2015 at 09:58:07AM +1100, Dave Chinner wrote:
> On Fri, Nov 13, 2015 at 05:06:47PM -0700, Ross Zwisler wrote:
> > To properly handle fsync/msync in an efficient way DAX needs to track dirty
> > pages so it is able to flush them durably to media on demand.
> > 
> > The tracking of dirty pages is done via the radix tree in struct
> > address_space.  This radix tree is already used by the page writeback
> > infrastructure for tracking dirty pages associated with an open file, and
> > it already has support for exceptional (non struct page*) entries.  We
> > build upon these features to add exceptional entries to the radix tree for
> > DAX dirty PMD or PTE pages at fault time.
> > 
> > When called as part of the msync/fsync flush path DAX queries the radix
> > tree for dirty entries, flushing them and then marking the PTE or PMD page
> > table entries as clean.  The step of cleaning the PTE or PMD entries is
> > necessary so that on subsequent writes to the same page we get a new write
> > fault allowing us to once again dirty the DAX tag in the radix tree.
> > 
> > Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
> > ---
> >  fs/dax.c            | 140 +++++++++++++++++++++++++++++++++++++++++++++++++---
> >  include/linux/dax.h |   1 +
> >  mm/huge_memory.c    |  14 +++---
> >  3 files changed, 141 insertions(+), 14 deletions(-)
> > 
> > diff --git a/fs/dax.c b/fs/dax.c
> > index 131fd35a..9ce6d1b 100644
> > --- a/fs/dax.c
> > +++ b/fs/dax.c
> > @@ -24,7 +24,9 @@
> >  #include <linux/memcontrol.h>
> >  #include <linux/mm.h>
> >  #include <linux/mutex.h>
> > +#include <linux/pagevec.h>
> >  #include <linux/pmem.h>
> > +#include <linux/rmap.h>
> >  #include <linux/sched.h>
> >  #include <linux/uio.h>
> >  #include <linux/vmstat.h>
> > @@ -287,6 +289,53 @@ static int copy_user_bh(struct page *to, struct buffer_head *bh,
> >  	return 0;
> >  }
> >  
> > +static int dax_dirty_pgoff(struct address_space *mapping, unsigned long pgoff,
> > +		void __pmem *addr, bool pmd_entry)
> > +{
> > +	struct radix_tree_root *page_tree = &mapping->page_tree;
> > +	int error = 0;
> > +	void *entry;
> > +
> > +	__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
> > +
> > +	spin_lock_irq(&mapping->tree_lock);
> > +	entry = radix_tree_lookup(page_tree, pgoff);
> > +	if (addr == NULL) {
> > +		if (entry)
> > +			goto dirty;
> > +		else {
> > +			WARN(1, "DAX pfn_mkwrite failed to find an entry");
> > +			goto out;
> > +		}
> > +	}
> > +
> > +	if (entry) {
> > +		if (pmd_entry && RADIX_DAX_TYPE(entry) == RADIX_DAX_PTE) {
> > +			radix_tree_delete(&mapping->page_tree, pgoff);
> > +			mapping->nrdax--;
> > +		} else
> > +			goto dirty;
> > +	}
> 
> Logic is pretty spagettied here. Perhaps:
> 
> 	entry = radix_tree_lookup(page_tree, pgoff);
> 	if (entry) {
> 		if (!pmd_entry || RADIX_DAX_TYPE(entry) == RADIX_DAX_PMD))
> 			goto dirty;
> 		radix_tree_delete(&mapping->page_tree, pgoff);
> 		mapping->nrdax--;
> 	} else {
> 		WARN_ON(!addr);
> 		goto out_unlock;
> 	}
> ....

I don't think that this works because now if !entry we unconditionally goto
out_unlock without inserting a new entry.  I'll try and simplify the logic and
add some comments.

> > +
> > +	BUG_ON(RADIX_DAX_TYPE(addr));
> > +	if (pmd_entry)
> > +		error = radix_tree_insert(page_tree, pgoff,
> > +				RADIX_DAX_PMD_ENTRY(addr));
> > +	else
> > +		error = radix_tree_insert(page_tree, pgoff,
> > +				RADIX_DAX_PTE_ENTRY(addr));
> > +
> > +	if (error)
> > +		goto out;
> > +
> > +	mapping->nrdax++;
> > + dirty:
> > +	radix_tree_tag_set(page_tree, pgoff, PAGECACHE_TAG_DIRTY);
> > + out:
> > +	spin_unlock_irq(&mapping->tree_lock);
> 
> label should be "out_unlock" rather "out" to indicate in the code
> that we are jumping to the correct spot in the error stack...

Sure, will do.

> > +			goto fallback;
> >  	}
> >  
> >   out:
> > @@ -689,15 +746,12 @@ EXPORT_SYMBOL_GPL(dax_pmd_fault);
> >   * dax_pfn_mkwrite - handle first write to DAX page
> >   * @vma: The virtual memory area where the fault occurred
> >   * @vmf: The description of the fault
> > - *
> >   */
> >  int dax_pfn_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
> >  {
> > -	struct super_block *sb = file_inode(vma->vm_file)->i_sb;
> > +	struct file *file = vma->vm_file;
> >  
> > -	sb_start_pagefault(sb);
> > -	file_update_time(vma->vm_file);
> > -	sb_end_pagefault(sb);
> > +	dax_dirty_pgoff(file->f_mapping, vmf->pgoff, NULL, false);
> >  	return VM_FAULT_NOPAGE;
> 
> This seems wrong - it's dropping the freeze protection on fault, and
> now the inode timestamp won't get updated, either.

Oh, that all still happens in the filesystem pfn_mkwrite code
(xfs_filemap_pfn_mkwrite() for XFS).  It needs to happen there, I think,
because we wanted to order it so that the filesystem freeze happens outside of
the XFS_MMAPLOCK_SHARED locking, as it does with the regular PMD and PTE fault
paths.

Prior to this patch set dax_pfn_mkwrite() was completely unused an was ready
to be removed as dead code - it's now being used by all filesystems just to
make sure we re-add the newly dirtied page to the radix tree dirty list.

> >  }
> >  EXPORT_SYMBOL_GPL(dax_pfn_mkwrite);
> > @@ -772,3 +826,77 @@ int dax_truncate_page(struct inode *inode, loff_t from, get_block_t get_block)
> >  	return dax_zero_page_range(inode, from, length, get_block);
> >  }
> >  EXPORT_SYMBOL_GPL(dax_truncate_page);
> > +
> > +static void dax_sync_entry(struct address_space *mapping, pgoff_t pgoff,
> > +		void *entry)
> > +{
> 
> dax_writeback_pgoff() seems like a more consistent name (consider
> dax_dirty_pgoff), and that we are actually doing a writeback
> operation, not a "sync" operation.

Sure, I'm fine with that change.

> > +	struct radix_tree_root *page_tree = &mapping->page_tree;
> > +	int type = RADIX_DAX_TYPE(entry);
> > +	size_t size;
> > +
> > +	BUG_ON(type != RADIX_DAX_PTE && type != RADIX_DAX_PMD);
> > +
> > +	spin_lock_irq(&mapping->tree_lock);
> > +	if (!radix_tree_tag_get(page_tree, pgoff, PAGECACHE_TAG_TOWRITE)) {
> > +		/* another fsync thread already wrote back this entry */
> > +		spin_unlock_irq(&mapping->tree_lock);
> > +		return;
> > +	}
> > +	radix_tree_tag_clear(page_tree, pgoff, PAGECACHE_TAG_TOWRITE);
> > +	radix_tree_tag_clear(page_tree, pgoff, PAGECACHE_TAG_DIRTY);
> > +	spin_unlock_irq(&mapping->tree_lock);
> > +
> > +	if (type == RADIX_DAX_PMD)
> > +		size = PMD_SIZE;
> > +	else
> > +		size = PAGE_SIZE;
> > +
> > +	wb_cache_pmem(RADIX_DAX_ADDR(entry), size);
> > +	pgoff_mkclean(pgoff, mapping);
> 
> This looks racy w.r.t. another operation setting the radix tree
> dirty tags. i.e. there is no locking to serialise marking the
> vma/pte clean and another operation marking the radix tree dirty.

I think you're right - I'll look into how to protect us from this race.  Thank
you for catching this.

> > +}
> > +
> > +/*
> > + * Flush the mapping to the persistent domain within the byte range of (start,
> > + * end). This is required by data integrity operations to ensure file data is on
> > + * persistent storage prior to completion of the operation. It also requires us
> > + * to clean the mappings (i.e. write -> RO) so that we'll get a new fault when
> > + * the file is written to again so we have an indication that we need to flush
> > + * the mapping if a data integrity operation takes place.
> > + *
> > + * We don't need commits to storage here - the filesystems will issue flushes
> > + * appropriately at the conclusion of the data integrity operation via REQ_FUA
> > + * writes or blkdev_issue_flush() commands.  This requires the DAX block device
> > + * to implement persistent storage domain fencing/commits on receiving a
> > + * REQ_FLUSH or REQ_FUA request so that this works as expected by the higher
> > + * layers.
> > + */
> > +void dax_fsync(struct address_space *mapping, loff_t start, loff_t end)
> > +{
> 
> dax_writeback_mapping_range()

Sure, I'm fine with that change.
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#1269372 — [PATCH v2 03/11] pmem: enable REQ_FUA/REQ_FLUSH handling

Currently the PMEM driver doesn't accept REQ_FLUSH or REQ_FUA bios.  These
are sent down via blkdev_issue_flush() in response to a fsync() or msync()
and are used by filesystems to order their metadata, among other things.

When we get an msync() or fsync() it is the responsibility of the DAX code
to flush all dirty pages to media.  The PMEM driver then just has issue a
wmb_pmem() in response to the REQ_FLUSH to ensure that before we return all
the flushed data has been durably stored on the media.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
---
 drivers/nvdimm/pmem.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
index 0ba6a97..b914d66 100644
--- a/drivers/nvdimm/pmem.c
+++ b/drivers/nvdimm/pmem.c
@@ -80,7 +80,7 @@ static void pmem_make_request(struct request_queue *q, struct bio *bio)
 	if (do_acct)
 		nd_iostat_end(bio, start);
 
-	if (bio_data_dir(bio))
+	if (bio_data_dir(bio) || (bio->bi_rw & (REQ_FLUSH|REQ_FUA)))
 		wmb_pmem();
 
 	bio_endio(bio);
@@ -189,6 +189,7 @@ static int pmem_attach_disk(struct device *dev,
 	blk_queue_physical_block_size(pmem->pmem_queue, PAGE_SIZE);
 	blk_queue_max_hw_sectors(pmem->pmem_queue, UINT_MAX);
 	blk_queue_bounce_limit(pmem->pmem_queue, BLK_BOUNCE_ANY);
+	blk_queue_flush(pmem->pmem_queue, REQ_FLUSH|REQ_FUA);
 	queue_flag_set_unlocked(QUEUE_FLAG_NONROT, pmem->pmem_queue);
 
 	disk = alloc_disk(0);
-- 
2.1.0

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#1269376 — Re: [PATCH v2 03/11] pmem: enable REQ_FUA/REQ_FLUSH handling

On Fri, Nov 13, 2015 at 4:06 PM, Ross Zwisler
<ross.zwisler@linux.intel.com> wrote:
> Currently the PMEM driver doesn't accept REQ_FLUSH or REQ_FUA bios.  These
> are sent down via blkdev_issue_flush() in response to a fsync() or msync()
> and are used by filesystems to order their metadata, among other things.
>
> When we get an msync() or fsync() it is the responsibility of the DAX code
> to flush all dirty pages to media.  The PMEM driver then just has issue a
> wmb_pmem() in response to the REQ_FLUSH to ensure that before we return all
> the flushed data has been durably stored on the media.
>
> Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>

Hmm, I'm not seeing why we need this patch.  If the actual flushing of
the cache is done by the core why does the driver need support
REQ_FLUSH?  Especially since it's just a couple instructions.  REQ_FUA
only makes sense if individual writes can bypass the "drive" cache,
but no I/O submitted to the driver proper is ever cached we always
flush it through to media.
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#1269382 — Re: [PATCH v2 03/11] pmem: enable REQ_FUA/REQ_FLUSH handling

[Multipart message — attachments visible in raw view] — view raw

On Nov 13, 2015, at 5:20 PM, Dan Williams <dan.j.williams@intel.com> wrote:
> 
> On Fri, Nov 13, 2015 at 4:06 PM, Ross Zwisler
> <ross.zwisler@linux.intel.com> wrote:
>> Currently the PMEM driver doesn't accept REQ_FLUSH or REQ_FUA bios.  These
>> are sent down via blkdev_issue_flush() in response to a fsync() or msync()
>> and are used by filesystems to order their metadata, among other things.
>> 
>> When we get an msync() or fsync() it is the responsibility of the DAX code
>> to flush all dirty pages to media.  The PMEM driver then just has issue a
>> wmb_pmem() in response to the REQ_FLUSH to ensure that before we return all
>> the flushed data has been durably stored on the media.
>> 
>> Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
> 
> Hmm, I'm not seeing why we need this patch.  If the actual flushing of
> the cache is done by the core why does the driver need support
> REQ_FLUSH?  Especially since it's just a couple instructions.  REQ_FUA
> only makes sense if individual writes can bypass the "drive" cache,
> but no I/O submitted to the driver proper is ever cached we always
> flush it through to media.

If the upper level filesystem gets an error when submitting a flush
request, then it assumes the underlying hardware is broken and cannot
be as aggressive in IO submission, but instead has to wait for in-flight
IO to complete.  Since FUA/FLUSH is basically a no-op for pmem devices,
it doesn't make sense _not_ to support this functionality.

Cheers, Andreas

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#1269393 — Re: [PATCH v2 03/11] pmem: enable REQ_FUA/REQ_FLUSH handling

On Fri, Nov 13, 2015 at 4:43 PM, Andreas Dilger <adilger@dilger.ca> wrote:
> On Nov 13, 2015, at 5:20 PM, Dan Williams <dan.j.williams@intel.com> wrote:
>>
>> On Fri, Nov 13, 2015 at 4:06 PM, Ross Zwisler
>> <ross.zwisler@linux.intel.com> wrote:
>>> Currently the PMEM driver doesn't accept REQ_FLUSH or REQ_FUA bios.  These
>>> are sent down via blkdev_issue_flush() in response to a fsync() or msync()
>>> and are used by filesystems to order their metadata, among other things.
>>>
>>> When we get an msync() or fsync() it is the responsibility of the DAX code
>>> to flush all dirty pages to media.  The PMEM driver then just has issue a
>>> wmb_pmem() in response to the REQ_FLUSH to ensure that before we return all
>>> the flushed data has been durably stored on the media.
>>>
>>> Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
>>
>> Hmm, I'm not seeing why we need this patch.  If the actual flushing of
>> the cache is done by the core why does the driver need support
>> REQ_FLUSH?  Especially since it's just a couple instructions.  REQ_FUA
>> only makes sense if individual writes can bypass the "drive" cache,
>> but no I/O submitted to the driver proper is ever cached we always
>> flush it through to media.
>
> If the upper level filesystem gets an error when submitting a flush
> request, then it assumes the underlying hardware is broken and cannot
> be as aggressive in IO submission, but instead has to wait for in-flight
> IO to complete.

Upper level filesystems won't get errors when the driver does not
support flush.  Those requests are ended cleanly in
generic_make_request_checks().  Yes, the fs still needs to wait for
outstanding I/O to complete but in the case of pmem all I/O is
synchronous.  There's never anything to await when flushing at the
pmem driver level.

> Since FUA/FLUSH is basically a no-op for pmem devices,
> it doesn't make sense _not_ to support this functionality.

Seems to be a nop either way.  Given that DAX may lead to dirty data
pending to the device in the cpu cache that a REQ_FLUSH request will
not touch, its better to leave it all to the mm core to handle.  I.e.
it doesn't make sense to call the driver just for two instructions
(sfence + pcommit) when the mm core is taking on the cache flushing.
Either handle it all in the mm or the driver, not a mixture.
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#1270136 — Re: [PATCH v2 03/11] pmem: enable REQ_FUA/REQ_FLUSH handling

On Fri 13-11-15 18:32:40, Dan Williams wrote:
> On Fri, Nov 13, 2015 at 4:43 PM, Andreas Dilger <adilger@dilger.ca> wrote:
> > On Nov 13, 2015, at 5:20 PM, Dan Williams <dan.j.williams@intel.com> wrote:
> >>
> >> On Fri, Nov 13, 2015 at 4:06 PM, Ross Zwisler
> >> <ross.zwisler@linux.intel.com> wrote:
> >>> Currently the PMEM driver doesn't accept REQ_FLUSH or REQ_FUA bios.  These
> >>> are sent down via blkdev_issue_flush() in response to a fsync() or msync()
> >>> and are used by filesystems to order their metadata, among other things.
> >>>
> >>> When we get an msync() or fsync() it is the responsibility of the DAX code
> >>> to flush all dirty pages to media.  The PMEM driver then just has issue a
> >>> wmb_pmem() in response to the REQ_FLUSH to ensure that before we return all
> >>> the flushed data has been durably stored on the media.
> >>>
> >>> Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
> >>
> >> Hmm, I'm not seeing why we need this patch.  If the actual flushing of
> >> the cache is done by the core why does the driver need support
> >> REQ_FLUSH?  Especially since it's just a couple instructions.  REQ_FUA
> >> only makes sense if individual writes can bypass the "drive" cache,
> >> but no I/O submitted to the driver proper is ever cached we always
> >> flush it through to media.
> >
> > If the upper level filesystem gets an error when submitting a flush
> > request, then it assumes the underlying hardware is broken and cannot
> > be as aggressive in IO submission, but instead has to wait for in-flight
> > IO to complete.
> 
> Upper level filesystems won't get errors when the driver does not
> support flush.  Those requests are ended cleanly in
> generic_make_request_checks().  Yes, the fs still needs to wait for
> outstanding I/O to complete but in the case of pmem all I/O is
> synchronous.  There's never anything to await when flushing at the
> pmem driver level.
> 
> > Since FUA/FLUSH is basically a no-op for pmem devices,
> > it doesn't make sense _not_ to support this functionality.
> 
> Seems to be a nop either way.  Given that DAX may lead to dirty data
> pending to the device in the cpu cache that a REQ_FLUSH request will
> not touch, its better to leave it all to the mm core to handle.  I.e.
> it doesn't make sense to call the driver just for two instructions
> (sfence + pcommit) when the mm core is taking on the cache flushing.
> Either handle it all in the mm or the driver, not a mixture.

So I think REQ_FLUSH requests *must* end up doing sfence + pcommit because
e.g. journal writes going through block layer or writes done through
dax_do_io() must be on permanent storage once REQ_FLUSH request finishes
and the way driver does IO doesn't guarantee this, does it?

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR
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