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Re: [PATCH v5 09/17] dax: coordinate locking for offsets in PMD range

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On Tue, Oct 11, 2016 at 09:04:09AM +0200, Jan Kara wrote:
> On Fri 07-10-16 15:08:56, Ross Zwisler wrote:
> > DAX radix tree locking currently locks entries based on the unique
> > combination of the 'mapping' pointer and the pgoff_t 'index' for the entry.
> > This works for PTEs, but as we move to PMDs we will need to have all the
> > offsets within the range covered by the PMD to map to the same bit lock.
> > To accomplish this, for ranges covered by a PMD entry we will instead lock
> > based on the page offset of the beginning of the PMD entry.  The 'mapping'
> > pointer is still used in the same way.
> > 
> > Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
> 
> The patch looks good to me. You can add:
> 
> Reviewed-by: Jan Kara <jack@suse.cz>
> 
> Just one thing which IMO deserves a comment below:
> 
> > @@ -448,9 +460,12 @@ restart:
> >  }
> >  
> >  void dax_wake_mapping_entry_waiter(struct address_space *mapping,
> > -				   pgoff_t index, bool wake_all)
> > +		pgoff_t index, void *entry, bool wake_all)
> >  {
> > -	wait_queue_head_t *wq = dax_entry_waitqueue(mapping, index);
> > +	struct exceptional_entry_key key;
> > +	wait_queue_head_t *wq;
> > +
> > +	wq = dax_entry_waitqueue(mapping, index, entry, &key);
> 
> So I believe we should comment above this function that the 'entry' it gets
> may be invalid by the time it gets it (we call it without tree_lock held so
> the passed entry may be changed in the radix tree as we work) but we use it
> only to find appropriate waitqueue where tasks sleep waiting for that old
> entry to unlock so we indeed wake up all tasks we need.

Added, thanks for the suggestion.

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[PATCH v5 00/17] re-enable DAX PMD support Ross Zwisler <ross.zwisler@linux.intel.com> - 2016-10-07 23:10 +0200
  [PATCH v5 07/17] dax: remove the last BUG_ON() from fs/dax.c Ross Zwisler <ross.zwisler@linux.intel.com> - 2016-10-07 23:10 +0200
    Re: [PATCH v5 07/17] dax: remove the last BUG_ON() from fs/dax.c Jan Kara <jack@suse.cz> - 2016-10-11 21:00 +0200
  [PATCH v5 04/17] ext2: remove support for DAX PMD faults Ross Zwisler <ross.zwisler@linux.intel.com> - 2016-10-07 23:20 +0200
  [PATCH v5 01/17] ext4: allow DAX writeback for hole punch Ross Zwisler <ross.zwisler@linux.intel.com> - 2016-10-07 23:20 +0200
  [PATCH v5 12/17] dax: add dax_iomap_sector() helper function Ross Zwisler <ross.zwisler@linux.intel.com> - 2016-10-07 23:20 +0200
    Re: [PATCH v5 12/17] dax: add dax_iomap_sector() helper function Christoph Hellwig <hch@lst.de> - 2016-10-10 17:50 +0200
    Re: [PATCH v5 12/17] dax: add dax_iomap_sector() helper function Jan Kara <jack@suse.cz> - 2016-10-11 20:50 +0200
  [PATCH v5 13/17] dax: dax_iomap_fault() needs to call iomap_end() Ross Zwisler <ross.zwisler@linux.intel.com> - 2016-10-07 23:20 +0200
    Re: [PATCH v5 13/17] dax: dax_iomap_fault() needs to call         iomap_end() Christoph Hellwig <hch@lst.de> - 2016-10-10 18:00 +0200
      Re: [PATCH v5 13/17] dax: dax_iomap_fault() needs to call iomap_end() Ross Zwisler <ross.zwisler@linux.intel.com> - 2016-10-11 00:10 +0200
    Re: [PATCH v5 13/17] dax: dax_iomap_fault() needs to call iomap_end() Jan Kara <jack@suse.cz> - 2016-10-11 20:50 +0200
  [PATCH v5 16/17] xfs: use struct iomap based DAX PMD fault path Ross Zwisler <ross.zwisler@linux.intel.com> - 2016-10-07 23:20 +0200
    Re: [PATCH v5 16/17] xfs: use struct iomap based DAX PMD fault path Jan Kara <jack@suse.cz> - 2016-10-11 20:50 +0200
  [PATCH v5 08/17] dax: consistent variable naming for DAX entries Ross Zwisler <ross.zwisler@linux.intel.com> - 2016-10-07 23:20 +0200
  [PATCH v5 05/17] ext2: return -EIO on ext2_iomap_end() failure Ross Zwisler <ross.zwisler@linux.intel.com> - 2016-10-07 23:20 +0200
    Re: [PATCH v5 05/17] ext2: return -EIO on ext2_iomap_end() failure Jan Kara <jack@suse.cz> - 2016-10-11 21:00 +0200
  [PATCH v5 03/17] dax: remove buffer_size_valid() Ross Zwisler <ross.zwisler@linux.intel.com> - 2016-10-07 23:20 +0200
  [PATCH v5 09/17] dax: coordinate locking for offsets in PMD range Ross Zwisler <ross.zwisler@linux.intel.com> - 2016-10-07 23:20 +0200
    Re: [PATCH v5 09/17] dax: coordinate locking for offsets in PMD         range Christoph Hellwig <hch@lst.de> - 2016-10-10 17:50 +0200
    Re: [PATCH v5 09/17] dax: coordinate locking for offsets in PMD range Jan Kara <jack@suse.cz> - 2016-10-11 20:50 +0200
      Re: [PATCH v5 09/17] dax: coordinate locking for offsets in PMD range Ross Zwisler <ross.zwisler@linux.intel.com> - 2016-10-11 23:20 +0200
  [PATCH v5 02/17] ext4: tell DAX the size of allocation holes Ross Zwisler <ross.zwisler@linux.intel.com> - 2016-10-07 23:20 +0200
  [PATCH v5 11/17] dax: correct dax iomap code namespace Ross Zwisler <ross.zwisler@linux.intel.com> - 2016-10-07 23:20 +0200
    Re: [PATCH v5 11/17] dax: correct dax iomap code namespace Christoph Hellwig <hch@lst.de> - 2016-10-09 17:30 +0200
      [PATCH] dax: correct dax iomap code namespace Ross Zwisler <ross.zwisler@linux.intel.com> - 2016-10-10 21:10 +0200
        Re: [PATCH] dax: correct dax iomap code namespace Dave Chinner <david@fromorbit.com> - 2016-10-10 22:50 +0200
  [PATCH v5 17/17] dax: remove "depends on BROKEN" from FS_DAX_PMD Ross Zwisler <ross.zwisler@linux.intel.com> - 2016-10-07 23:20 +0200
  [PATCH v5 14/17] dax: move RADIX_DAX_* defines to dax.h Ross Zwisler <ross.zwisler@linux.intel.com> - 2016-10-07 23:20 +0200
    Re: [PATCH v5 14/17] dax: move RADIX_DAX_* defines to dax.h Christoph Hellwig <hch@lst.de> - 2016-10-10 18:00 +0200
    Re: [PATCH v5 14/17] dax: move RADIX_DAX_* defines to dax.h Jan Kara <jack@suse.cz> - 2016-10-11 20:50 +0200
  [PATCH v5 10/17] dax: remove dax_pmd_fault() Ross Zwisler <ross.zwisler@linux.intel.com> - 2016-10-07 23:20 +0200
  [PATCH v5 15/17] dax: add struct iomap based DAX PMD support Ross Zwisler <ross.zwisler@linux.intel.com> - 2016-10-07 23:20 +0200
    Re: [PATCH v5 15/17] dax: add struct iomap based DAX PMD support Christoph Hellwig <hch@lst.de> - 2016-10-10 18:00 +0200
      Re: [PATCH v5 15/17] dax: add struct iomap based DAX PMD support Ross Zwisler <ross.zwisler@linux.intel.com> - 2016-10-11 00:10 +0200
      Re: [PATCH v5 15/17] dax: add struct iomap based DAX PMD support Ross Zwisler <ross.zwisler@linux.intel.com> - 2016-10-11 23:50 +0200
    Re: [PATCH v5 15/17] dax: add struct iomap based DAX PMD support Jan Kara <jack@suse.cz> - 2016-10-11 21:00 +0200
      Re: [PATCH v5 15/17] dax: add struct iomap based DAX PMD support Ross Zwisler <ross.zwisler@linux.intel.com> - 2016-10-12 01:00 +0200
        Re: [PATCH v5 15/17] dax: add struct iomap based DAX PMD support Jan Kara <jack@suse.cz> - 2016-10-12 09:50 +0200

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