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authorDave Chinner <dchinner@redhat.com>2010-11-30 15:16:16 +1100
committerAlex Elder <aelder@sgi.com>2010-12-01 07:40:20 -0600
commit90810b9e82a36c3c57c1aeb8b2918b242a130b26 (patch)
tree2fdb8bd75866fc3d61cb7fe2f2cc26f0e6895641
parentc726de4409a8d3a03877b1ef4342bfe8a15f5e5e (diff)
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xfs: push stale, pinned buffers on trylock failures
As reported by Nick Piggin, XFS is suffering from long pauses under highly concurrent workloads when hosted on ramdisks. The problem is that an inode buffer is stuck in the pinned state in memory and as a result either the inode buffer or one of the inodes within the buffer is stopping the tail of the log from being moved forward. The system remains in this state until a periodic log force issued by xfssyncd causes the buffer to be unpinned. The main problem is that these are stale buffers, and are hence held locked until the transaction/checkpoint that marked them state has been committed to disk. When the filesystem gets into this state, only the xfssyncd can cause the async transactions to be committed to disk and hence unpin the inode buffer. This problem was encountered when scaling the busy extent list, but only the blocking lock interface was fixed to solve the problem. Extend the same fix to the buffer trylock operations - if we fail to lock a pinned, stale buffer, then force the log immediately so that when the next attempt to lock it comes around, it will have been unpinned. Signed-off-by: Dave Chinner <dchinner@redhat.com> Reviewed-by: Christoph Hellwig <hch@lst.de>
-rw-r--r--fs/xfs/linux-2.6/xfs_buf.c35
1 files changed, 16 insertions, 19 deletions
diff --git a/fs/xfs/linux-2.6/xfs_buf.c b/fs/xfs/linux-2.6/xfs_buf.c
index aa1d353def2..4c5deb6e9e3 100644
--- a/fs/xfs/linux-2.6/xfs_buf.c
+++ b/fs/xfs/linux-2.6/xfs_buf.c
@@ -488,29 +488,16 @@ found:
spin_unlock(&pag->pag_buf_lock);
xfs_perag_put(pag);
- /* Attempt to get the semaphore without sleeping,
- * if this does not work then we need to drop the
- * spinlock and do a hard attempt on the semaphore.
- */
- if (down_trylock(&bp->b_sema)) {
+ if (xfs_buf_cond_lock(bp)) {
+ /* failed, so wait for the lock if requested. */
if (!(flags & XBF_TRYLOCK)) {
- /* wait for buffer ownership */
xfs_buf_lock(bp);
XFS_STATS_INC(xb_get_locked_waited);
} else {
- /* We asked for a trylock and failed, no need
- * to look at file offset and length here, we
- * know that this buffer at least overlaps our
- * buffer and is locked, therefore our buffer
- * either does not exist, or is this buffer.
- */
xfs_buf_rele(bp);
XFS_STATS_INC(xb_busy_locked);
return NULL;
}
- } else {
- /* trylock worked */
- XB_SET_OWNER(bp);
}
if (bp->b_flags & XBF_STALE) {
@@ -876,10 +863,18 @@ xfs_buf_rele(
*/
/*
- * Locks a buffer object, if it is not already locked.
- * Note that this in no way locks the underlying pages, so it is only
- * useful for synchronizing concurrent use of buffer objects, not for
- * synchronizing independent access to the underlying pages.
+ * Locks a buffer object, if it is not already locked. Note that this in
+ * no way locks the underlying pages, so it is only useful for
+ * synchronizing concurrent use of buffer objects, not for synchronizing
+ * independent access to the underlying pages.
+ *
+ * If we come across a stale, pinned, locked buffer, we know that we are
+ * being asked to lock a buffer that has been reallocated. Because it is
+ * pinned, we know that the log has not been pushed to disk and hence it
+ * will still be locked. Rather than continuing to have trylock attempts
+ * fail until someone else pushes the log, push it ourselves before
+ * returning. This means that the xfsaild will not get stuck trying
+ * to push on stale inode buffers.
*/
int
xfs_buf_cond_lock(
@@ -890,6 +885,8 @@ xfs_buf_cond_lock(
locked = down_trylock(&bp->b_sema) == 0;
if (locked)
XB_SET_OWNER(bp);
+ else if (atomic_read(&bp->b_pin_count) && (bp->b_flags & XBF_STALE))
+ xfs_log_force(bp->b_target->bt_mount, 0);
trace_xfs_buf_cond_lock(bp, _RET_IP_);
return locked ? 0 : -EBUSY;