xfs: retry allocations when locality-based search fails

If a realtime allocation fails because we can't find a sufficiently
large free extent satisfying locality rules, relax the locality rules
and try again.  This reduces the occurrence of short writes to realtime
files when the write size is large and the free space is fragmented.

This was originally discovered by running generic/186 with the realtime
reflink patchset and a 128k cow extent size hint, but the short write
symptoms can manifest with a 128k extent size hint and no reflink, so
apply the fix now.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Allison Henderson <allison.henderson@oracle.com>

diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c
index c9381bf4f04bfa5b3e0a5202c3814c024e52edbc..0936f3a96fe6e845007e444bad9a33fa0e8fa12a 100644 (file)
--- a/fs/xfs/xfs_bmap_util.c
+++ b/fs/xfs/xfs_bmap_util.c
@@ -84,6 +84,7 @@ xfs_bmap_rtalloc(
        xfs_extlen_t            minlen = mp->m_sb.sb_rextsize;
        xfs_extlen_t            raminlen;
        bool                    rtlocked = false;
+       bool                    ignore_locality = false;
        int                     error;
 
        align = xfs_get_extsz_hint(ap->ip);
@@ -158,7 +159,10 @@ retry:
        /*
         * Realtime allocation, done through xfs_rtallocate_extent.
         */
-       do_div(ap->blkno, mp->m_sb.sb_rextsize);
+       if (ignore_locality)
+               ap->blkno = 0;
+       else
+               do_div(ap->blkno, mp->m_sb.sb_rextsize);
        rtb = ap->blkno;
        ap->length = ralen;
        raminlen = max_t(xfs_extlen_t, 1, minlen / mp->m_sb.sb_rextsize);
@@ -197,6 +201,15 @@ retry:
                goto retry;
        }
 
+       if (!ignore_locality && ap->blkno != 0) {
+               /*
+                * If we can't allocate near a specific rt extent, try again
+                * without locality criteria.
+                */
+               ignore_locality = true;
+               goto retry;
+       }
+
        ap->blkno = NULLFSBLOCK;
        ap->length = 0;
        return 0;