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Re: [PATCH 04/27] xfs: don't use speculative prealloc for small files

To: Brian Foster <bfoster@xxxxxxxxxx>
Subject: Re: [PATCH 04/27] xfs: don't use speculative prealloc for small files
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Thu, 13 Jun 2013 10:50:50 +1000
Cc: xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <51B89D58.80108@xxxxxxxxxx>
References: <1371032567-21772-1-git-send-email-david@xxxxxxxxxxxxx> <1371032567-21772-5-git-send-email-david@xxxxxxxxxxxxx> <51B89D58.80108@xxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Wed, Jun 12, 2013 at 12:10:00PM -0400, Brian Foster wrote:
> On 06/12/2013 06:22 AM, Dave Chinner wrote:
> > From: Dave Chinner <dchinner@xxxxxxxxxx>
> > 
> ...
> > ---
> >  fs/xfs/xfs_iomap.c |   13 +++++++++++++
> >  1 file changed, 13 insertions(+)
> > 
> > diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
> > index 8f8aaee..14be676 100644
> > --- a/fs/xfs/xfs_iomap.c
> > +++ b/fs/xfs/xfs_iomap.c
> > @@ -284,6 +284,15 @@ xfs_iomap_eof_want_preallocate(
> >             return 0;
> >  
> >     /*
> > +    * If the file is smaller than the minimum prealloc and we are using
> > +    * dynamic preallocation, don't do any preallocation at all as it is
> > +    * likely this is the only write to the file that is going to be done.
> > +    */
> > +   if (!(mp->m_flags & XFS_MOUNT_DFLT_IOSIZE) &&
> > +       XFS_ISIZE(ip) < mp->m_writeio_blocks)
> > +           return 0;
> > +
> 
> I stuck this on a box, got a 64k prealloc on an 8k file and then noticed
> this was comparing inode size against a block count. This should
> probably be:
> 
>       XFS_ISIZE(ip) < XFS_FSB_TO_B(mp, mp->m_writeio_blocks)
> 
> Given that, we avoid preallocs entirely until the file size reaches the
> minimum write size (assuming dynamic prealloc mode).

Doh! Will fix.

Cheers

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx

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