Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking infrastructure and convert ext4 to use it

From	NeilBrown <neilb@suse.com>
Newsgroups	linux.kernel
Subject	Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking infrastructure and convert ext4 to use it
Date	2017-04-06 07:20 +0200
Message-ID	<tt7ZT-4cz-3@gated-at.bofh.it> (permalink)
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On Wed, Apr 05 2017, Matthew Wilcox wrote:

> On Thu, Apr 06, 2017 at 10:02:48AM +1000, NeilBrown wrote:
>> If you are concerned about space in 'struct address_space', just prune
>> some wastage.
>
> I'm trying to (via wlists).  still buggy though.

Cool.
(I wonder what a wlist is.... weighted list?)

>
>> The "host" field brings no value.  It is only ever assigned in
>> inode_init_always():
>> 
>> 	struct address_space *const mapping = &inode->i_data;
>> ......
>> 	mapping->host = inode;
>> 
>> So you could change all references to use
>>    container_of(mapping, struct inode, i_data)
>
> Alas, no:
>
> drivers/dax/dax.c:      inode->i_mapping->host = dax_dev->inode;

	inode->i_mapping = dax_dev->inode->i_mapping;
	inode->i_mapping->host = dax_dev->inode;
so that second line is equivalent to
        dax_dev->inode->i_mapping->host = dax_dev->inode;
so inode->mapping->host leads back to inode.  So this doesn't break the
invariant.

> fs/gfs2/glock.c:                mapping->host = s->s_bdev->bd_inode;
> fs/gfs2/ops_fstype.c:   mapping->host = sb->s_bdev->bd_inode;

Hmm.. that's weird.  I cannot quite follow what is happening there.
It creates an address-space for metadata which doesn't have a real
inode, and borrows bits of the bdev inode ... possibly just to be able
to find the blocksize deep in buffer.c or similar.
I suspect that using an 'inode' instead of a 'mapping' would make the
code clearer.

> fs/nilfs2/page.c:       mapping->host = inode;

A nilfs inode is allocated with 2 address spaces,
one for the data and one for btree indexing metadata.
And then there are a couple of extra address spaces for the
global metadata-file (mtd).

I wonder what the ->host pointer is actually used for.
buffer.c uses it:
 - to mark the inode 'dirty' when the page is marked dirty
 - to find the blocksize of the inode, for creating buffer_heads
 - find the size of the mapping (i_size)

I could probably argue that the 'dirty' flag (at least for the data) and
the size really belong in the address_space, not in the inode.
The blocksize, I'm less sure of.

I suspect gfs2 and nilfs2 could be changed to allocate a separate inode
(instead of address_space), or to not make use of the ->host pointer.
It would be more work than I at first thought though.

Thanks,
NeilBrown

Thread

[RFC PATCH 0/4] fs: introduce new writeback error tracking infrastructure and convert ext4 to use it Jeff Layton <jlayton@redhat.com> - 2017-03-31 21:30 +0200
  [RFC PATCH 2/4] dax: set errors in mapping when writeback fails Jeff Layton <jlayton@redhat.com> - 2017-03-31 21:30 +0200
  [RFC PATCH 1/4] fs: new infrastructure for writeback error handling and reporting Jeff Layton <jlayton@redhat.com> - 2017-03-31 21:30 +0200
    Re: [RFC PATCH 1/4] fs: new infrastructure for writeback error  handling and reporting Nikolay Borisov <nborisov@suse.com> - 2017-04-03 09:20 +0200
      Re: [RFC PATCH 1/4] fs: new infrastructure for writeback error  handling and reporting Jeff Layton <jlayton@redhat.com> - 2017-04-03 12:30 +0200
    Re: [RFC PATCH 1/4] fs: new infrastructure for writeback error  handling and reporting Matthew Wilcox <willy@infradead.org> - 2017-04-03 16:50 +0200
      Re: [RFC PATCH 1/4] fs: new infrastructure for writeback error  handling and reporting Jeff Layton <jlayton@redhat.com> - 2017-04-03 17:30 +0200
        Re: [RFC PATCH 1/4] fs: new infrastructure for writeback error  handling and reporting Matthew Wilcox <willy@infradead.org> - 2017-04-03 18:20 +0200
          Re: [RFC PATCH 1/4] fs: new infrastructure for writeback error  handling and reporting Jeff Layton <jlayton@redhat.com> - 2017-04-03 18:40 +0200
  [RFC PATCH 4/4] ext4: wire it up to the new writeback error reporting infrastructure Jeff Layton <jlayton@redhat.com> - 2017-03-31 21:30 +0200
  Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking infrastructure and convert ext4 to use it NeilBrown <neilb@suse.com> - 2017-04-03 06:30 +0200
    Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Jeff Layton <jlayton@redhat.com> - 2017-04-03 12:30 +0200
      Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Matthew Wilcox <willy@infradead.org> - 2017-04-03 16:40 +0200
        Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Jeff Layton <jlayton@redhat.com> - 2017-04-03 19:50 +0200
          Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Jeremy Allison <jra@samba.org> - 2017-04-03 20:20 +0200
            Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Jeff Layton <jlayton@redhat.com> - 2017-04-03 20:20 +0200
              Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Jeremy Allison <jra@samba.org> - 2017-04-03 20:40 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Jeremy Allison <jra@samba.org> - 2017-04-03 20:50 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Jeff Layton <jlayton@redhat.com> - 2017-04-03 20:50 +0200
          Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Matthew Wilcox <willy@infradead.org> - 2017-04-03 21:20 +0200
            Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Jeff Layton <jlayton@redhat.com> - 2017-04-03 22:20 +0200
              Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Matthew Wilcox <willy@infradead.org> - 2017-04-04 04:50 +0200
              Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking infrastructure and convert ext4 to use it NeilBrown <neilb@suse.com> - 2017-04-04 05:10 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Jeff Layton <jlayton@redhat.com> - 2017-04-04 13:50 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking infrastructure and convert ext4 to use it NeilBrown <neilb@suse.com> - 2017-04-05 00:50 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Matthew Wilcox <willy@infradead.org> - 2017-04-04 14:00 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Jeff Layton <jlayton@redhat.com> - 2017-04-04 14:20 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Matthew Wilcox <willy@infradead.org> - 2017-04-04 18:20 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Jeff Layton <jlayton@redhat.com> - 2017-04-04 18:30 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Matthew Wilcox <willy@infradead.org> - 2017-04-04 19:10 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Jeff Layton <jlayton@redhat.com> - 2017-04-04 20:10 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking infrastructure and convert ext4 to use it NeilBrown <neilb@suse.com> - 2017-04-05 01:00 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Jeff Layton <jlayton@redhat.com> - 2017-04-05 22:00 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Matthew Wilcox <willy@infradead.org> - 2017-04-05 23:10 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking infrastructure and convert ext4 to use it NeilBrown <neilb@suse.com> - 2017-04-06 02:30 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking infrastructure and convert ext4 to use it NeilBrown <neilb@suse.com> - 2017-04-06 02:10 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Matthew Wilcox <willy@infradead.org> - 2017-04-06 05:00 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking infrastructure and convert ext4 to use it NeilBrown <neilb@suse.com> - 2017-04-06 07:20 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Matthew Wilcox <willy@infradead.org> - 2017-04-06 15:40 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking infrastructure and convert ext4 to use it NeilBrown <neilb@suse.com> - 2017-04-07 00:00 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Jeff Layton <jlayton@redhat.com> - 2017-04-06 16:10 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Jeff Layton <jlayton@redhat.com> - 2017-04-06 21:20 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Matthew Wilcox <willy@infradead.org> - 2017-04-06 22:20 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Jeff Layton <jlayton@redhat.com> - 2017-04-07 15:20 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking infrastructure and convert ext4 to use it NeilBrown <neilb@suse.com> - 2017-04-10 01:20 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Jeff Layton <jlayton@redhat.com> - 2017-04-10 15:30 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking infrastructure and convert ext4 to use it NeilBrown <neilb@suse.com> - 2017-04-07 00:20 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking infrastructure and convert ext4 to use it NeilBrown <neilb@suse.com> - 2017-04-05 01:20 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Jeff Layton <jlayton@redhat.com> - 2017-04-05 13:20 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking infrastructure and convert ext4 to use it NeilBrown <neilb@suse.com> - 2017-04-06 02:50 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Theodore Ts'o <tytso@mit.edu> - 2017-04-04 15:40 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking infrastructure and convert ext4 to use it NeilBrown <neilb@suse.com> - 2017-04-05 00:30 +0200
    Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Matthew Wilcox <willy@infradead.org> - 2017-04-03 17:00 +0200

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