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authorDave Chinner <dchinner@redhat.com>2011-11-19 13:13:40 -0500
committerGreg Kroah-Hartman <gregkh@suse.de>2011-11-26 09:10:05 -0800
commit16ba92e591d31d3213956e581867f46892648038 (patch)
tree60eb2e93d8edbdc1397ad805e47a17f237e10199
parentafd717d6cd334fc89f3ac938e19aade2f939b629 (diff)
downloadlinux-linaro-stable-16ba92e591d31d3213956e581867f46892648038.tar.gz
xfs: dont serialise direct IO reads on page cache
commit 0c38a2512df272b14ef4238b476a2e4f70da1479 upstream. There is no need to grab the i_mutex of the IO lock in exclusive mode if we don't need to invalidate the page cache. Taking these locks on every direct IO effective serialises them as taking the IO lock in exclusive mode has to wait for all shared holders to drop the lock. That only happens when IO is complete, so effective it prevents dispatch of concurrent direct IO reads to the same inode. Fix this by taking the IO lock shared to check the page cache state, and only then drop it and take the IO lock exclusively if there is work to be done. Hence for the normal direct IO case, no exclusive locking will occur. Signed-off-by: Dave Chinner <dchinner@redhat.com> Tested-by: Joern Engel <joern@logfs.org> Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alex Elder <aelder@sgi.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
-rw-r--r--fs/xfs/linux-2.6/xfs_file.c17
1 files changed, 14 insertions, 3 deletions
diff --git a/fs/xfs/linux-2.6/xfs_file.c b/fs/xfs/linux-2.6/xfs_file.c
index 7f782af2..93cc02d 100644
--- a/fs/xfs/linux-2.6/xfs_file.c
+++ b/fs/xfs/linux-2.6/xfs_file.c
@@ -309,7 +309,19 @@ xfs_file_aio_read(
if (XFS_FORCED_SHUTDOWN(mp))
return -EIO;
- if (unlikely(ioflags & IO_ISDIRECT)) {
+ /*
+ * Locking is a bit tricky here. If we take an exclusive lock
+ * for direct IO, we effectively serialise all new concurrent
+ * read IO to this file and block it behind IO that is currently in
+ * progress because IO in progress holds the IO lock shared. We only
+ * need to hold the lock exclusive to blow away the page cache, so
+ * only take lock exclusively if the page cache needs invalidation.
+ * This allows the normal direct IO case of no page cache pages to
+ * proceeed concurrently without serialisation.
+ */
+ xfs_rw_ilock(ip, XFS_IOLOCK_SHARED);
+ if ((ioflags & IO_ISDIRECT) && inode->i_mapping->nrpages) {
+ xfs_rw_iunlock(ip, XFS_IOLOCK_SHARED);
xfs_rw_ilock(ip, XFS_IOLOCK_EXCL);
if (inode->i_mapping->nrpages) {
@@ -322,8 +334,7 @@ xfs_file_aio_read(
}
}
xfs_rw_ilock_demote(ip, XFS_IOLOCK_EXCL);
- } else
- xfs_rw_ilock(ip, XFS_IOLOCK_SHARED);
+ }
trace_xfs_file_read(ip, size, iocb->ki_pos, ioflags);