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authorDave Chinner <dchinner@redhat.com>2013-01-21 23:53:54 +1100
committerBen Myers <bpm@sgi.com>2013-01-28 12:50:50 -0600
commitf2a459565b02b60408f3f2e5ca992a031319712b (patch)
tree1521bd5d0e47e5bd23ecfcde1e3763a4491ed2ae /fs/xfs
parenteb178619f930fa2ba2348de332a1ff1c66a31424 (diff)
xfs: limit speculative prealloc near ENOSPC thresholds
There is a window on small filesytsems where specualtive preallocation can be larger than that ENOSPC throttling thresholds, resulting in specualtive preallocation trying to reserve more space than there is space available. This causes immediate ENOSPC to be triggered, prealloc to be turned off and flushing to occur. One the next write (i.e. next 4k page), we do exactly the same thing, and so effective drive into synchronous 4k writes by triggering ENOSPC flushing on every page while in the window between the prealloc size and the ENOSPC prealloc throttle threshold. Fix this by checking to see if the prealloc size would consume all free space, and throttle it appropriately to avoid premature ENOSPC... Signed-off-by: Dave Chinner <dchinner@redhat.com> Reviewed-by: Brian Foster <bfoster@redhat.com> Signed-off-by: Ben Myers <bpm@sgi.com>
Diffstat (limited to 'fs/xfs')
-rw-r--r--fs/xfs/xfs_iomap.c9
1 files changed, 9 insertions, 0 deletions
diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index add06b4e9a6..364818eef40 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -351,6 +351,15 @@ xfs_iomap_prealloc_size(
}
if (shift)
alloc_blocks >>= shift;
+
+ /*
+ * If we are still trying to allocate more space than is
+ * available, squash the prealloc hard. This can happen if we
+ * have a large file on a small filesystem and the above
+ * lowspace thresholds are smaller than MAXEXTLEN.
+ */
+ while (alloc_blocks >= freesp)
+ alloc_blocks >>= 4;
}
if (alloc_blocks < mp->m_writeio_blocks)