RE: A blocksize problem about dax and ext4

From	"Elliott, Robert (Persistent Memory)" <elliott@hpe.com>
Newsgroups	linux.kernel
Subject	RE: A blocksize problem about dax and ext4
Date	2015-12-24 13:30 +0100
Message-ID	<qJdbQ-6E5-17@gated-at.bofh.it> (permalink)
References	(4 earlier) <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> <qJba2-5to-17@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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> -----Original Message-----
> From: Christoph Hellwig [mailto:hch@infradead.org]
> Sent: Thursday, December 24, 2015 4:11 AM
> Subject: Re: A blocksize problem about dax and ext4
> 
> 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.

I think that's a future goal.

Currently, the checks are like this:

	if (sb->s_blocksize != PAGE_SIZE) {
		xfs_alert(mp,
		"Filesystem block size invalid for DAX Turning DAX off.");


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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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