understanding speculative preallocation

[Jason Rosenberg]

Thanks Ben,

This is helpful.


On Fri, Jul 26, 2013 at 4:50 PM, Ben Myers <bpm at sgi.com> wrote:

> Hi Jason,
>
> On Fri, Jul 26, 2013 at 04:38:21PM -0400, Jason Rosenberg wrote:
> > Thanks for the info (most of it was, in fact, news to me).  I'm an
> > application developer trying to debug a disk space problem, that's all.
>  So
> > far, I've tracked it down to being an XFS issue.
>
> The speculative block reservations have been an issue for awhile.  You are
> not
> the first person to take issue with it.
>
> > Regardless, is there a version history for XFS vis-a-via mainline Linux?
>
> You can find a full version history for XFS back to 2.6.12 or so here:
> http://oss.sgi.com/cgi-bin/gitweb.cgi?p=xfs/xfs.git;a=summary
>
> If you're interested in going older than that look here:
> http://oss.sgi.com/cgi-bin/gitweb.cgi?p=archive/xfs-import.git;a=summary
>
> The function you'll most likely want to track is xfs_iomap_write_delay,
> which
> calls xfs_iomap_eof_want_preallocate, both of which are in
> fs/xfs/xfs_iomap.c.
>
> Recently Brian Foster added a scanner to remove the speculative block
> reservations on a timer which may give you some relief.  See
> xfs_queue_eofblocks in fs/xfs/xfs_icache.c
>
> Regards,
>         Ben
>
>
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