Re: [PATCH] xfs: Don't flush inodes when project quota exceeded

[Dave Chinner <david@fromorbit.com>]

On Mon, Nov 19, 2012 at 10:39:13PM +0100, Jan Kara wrote:
> On Tue 13-11-12 01:36:13, Jan Kara wrote:
> > When project quota gets exceeded xfs_iomap_write_delay() ends up flushing
> > inodes because ENOSPC gets returned from xfs_bmapi_delay() instead of EDQUOT.
> > This makes handling of writes over project quota rather slow as a simple test
> > program shows:
> > 	fd = open(argv[1], O_WRONLY | O_CREAT | O_TRUNC, 0644);
> > 	for (i = 0; i < 50000; i++)
> > 		pwrite(fd, buf, 4096, i*4096);
> > 
> > Writing 200 MB like this into a directory with 100 MB project quota takes
> > around 6 minutes while it takes about 2 seconds with this patch applied. This
> > actually happens in a real world load when nfs pushes data into a directory
> > which is over project quota.
> > 
> > Fix the problem by replacing XFS_QMOPT_ENOSPC flag with XFS_QMOPT_EPDQUOT.
> > That makes xfs_trans_reserve_quota_bydquots() return new error EPDQUOT when
> > project quota is exceeded. xfs_bmapi_delay() then uses this flag so that
> > xfs_iomap_write_delay() can distinguish real ENOSPC (requiring flushing)
> > from exceeded project quota (not requiring flushing).
> > 
> > As a side effect this patch fixes inconsistency where e.g. xfs_create()
> > returned EDQUOT even when project quota was exceeded.
>   Ping? Any opinions?

FWIW, it doesn't look like it'll apply to a current XFs tree:

> > @@ -441,8 +442,11 @@ retry:
> >  	 */
> >  	if (nimaps == 0) {
> >  		trace_xfs_delalloc_enospc(ip, offset, count);
> > -		if (flushed)
> > -			return XFS_ERROR(error ? error : ENOSPC);
> > +		if (flushed) {
> > +			if (error == 0 || error == EPDQUOT)
> > +				error = ENOSPC;
> > +			return XFS_ERROR(error);
> > +		}
> >  
> >  		if (error == ENOSPC) {
> >  			xfs_iunlock(ip, XFS_ILOCK_EXCL);

This xfs_iomap_write_delay() looks like this now:

        /*
         * If bmapi returned us nothing, we got either ENOSPC or EDQUOT. Retry
         * without EOF preallocation.
         */
        if (nimaps == 0) {
                trace_xfs_delalloc_enospc(ip, offset, count);
                if (prealloc) {
                        prealloc = 0;
                        error = 0;
                        goto retry;
                }
                return XFS_ERROR(error ? error : ENOSPC);
        }

The flushing is now way up in xfs_file_buffered_aio_write(), and the
implementation of xfs_flush_inodes() has changed as well. Hence it
may or may not behave differently not....

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

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