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

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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.

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

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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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