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Re: A blocksize problem about dax and ext4

From Christoph Hellwig <hch@infradead.org>
Newsgroups linux.kernel
Subject Re: A blocksize problem about dax and ext4
Date 2015-12-24 11:20 +0100
Message-ID <qJba2-5to-17@gated-at.bofh.it> (permalink)
References (3 earlier) <qJ1DK-83A-57@gated-at.bofh.it> <qJ2q6-8kk-13@gated-at.bofh.it> <qJ2q6-8kk-11@gated-at.bofh.it> <qJ48x-WX-7@gated-at.bofh.it> <qJ48x-WX-5@gated-at.bofh.it>
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On Thu, Dec 24, 2015 at 02:47:07AM +0000, Elliott, Robert (Persistent Memory) wrote:
> > Did you mean that I should make the blocksize bigger until the mount
> > command tell me that dax is enabled?
> 
> To really use DAX, the filesystem block size must match the
> system CPU's page size, which is probably 4096 bytes.

No, it doesn't.  File you use for DAX must be aligne at page size
granularity.  For XFS you could do this with the per-inode extent size
hint for example even if the overall block size is smaller.
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Thread

RE: A blocksize problem about dax and ext4 "Elliott, Robert (Persistent Memory)" <elliott@hpe.com> - 2015-12-23 22:20 +0100
  Re: A blocksize problem about dax and ext4 Dave Chinner <david@fromorbit.com> - 2015-12-24 01:10 +0100
    Re: A blocksize problem about dax and ext4 Dan Williams <dan.j.williams@intel.com> - 2015-12-24 02:00 +0100
      RE: A blocksize problem about dax and ext4 "Elliott, Robert (Persistent Memory)" <elliott@hpe.com> - 2015-12-24 03:50 +0100
        Re: A blocksize problem about dax and ext4 Christoph Hellwig <hch@infradead.org> - 2015-12-24 11:20 +0100
          RE: A blocksize problem about dax and ext4 "Elliott, Robert (Persistent Memory)" <elliott@hpe.com> - 2015-12-24 13:30 +0100

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