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authorTheodore Ts'o <tytso@mit.edu>2013-04-21 16:47:54 -0400
committerTheodore Ts'o <tytso@mit.edu>2013-04-21 16:47:54 -0400
commitf783f091e49ce4896e6b026af82d76e0537c6089 (patch)
tree0ff78a05254d4b996bb027d9fac9969d1d6e0b07 /fs/jbd2
parent13fca323e9a8b63c08de7a4e05d3c702516b535d (diff)
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jbd2: trace when lock_buffer in do_get_write_access takes a long time
While investigating interactivity problems it was clear that processes sometimes stall for long periods of times if an attempt is made to lock a buffer which is undergoing writeback. It would stall in a trace looking something like [<ffffffff811a39de>] __lock_buffer+0x2e/0x30 [<ffffffff8123a60f>] do_get_write_access+0x43f/0x4b0 [<ffffffff8123a7cb>] jbd2_journal_get_write_access+0x2b/0x50 [<ffffffff81220f79>] __ext4_journal_get_write_access+0x39/0x80 [<ffffffff811f3198>] ext4_reserve_inode_write+0x78/0xa0 [<ffffffff811f3209>] ext4_mark_inode_dirty+0x49/0x220 [<ffffffff811f57d1>] ext4_dirty_inode+0x41/0x60 [<ffffffff8119ac3e>] __mark_inode_dirty+0x4e/0x2d0 [<ffffffff8118b9b9>] update_time+0x79/0xc0 [<ffffffff8118ba98>] file_update_time+0x98/0x100 [<ffffffff81110ffc>] __generic_file_aio_write+0x17c/0x3b0 [<ffffffff811112aa>] generic_file_aio_write+0x7a/0xf0 [<ffffffff811ea853>] ext4_file_write+0x83/0xd0 [<ffffffff81172b23>] do_sync_write+0xa3/0xe0 [<ffffffff811731ae>] vfs_write+0xae/0x180 [<ffffffff8117361d>] sys_write+0x4d/0x90 [<ffffffff8159d62d>] system_call_fastpath+0x1a/0x1f [<ffffffffffffffff>] 0xffffffffffffffff Signed-off-by: Mel Gorman <mgorman@suse.de> Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Diffstat (limited to 'fs/jbd2')
-rw-r--r--fs/jbd2/transaction.c8
1 files changed, 8 insertions, 0 deletions
diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
index a1920da22802..10f524c59ea8 100644
--- a/fs/jbd2/transaction.c
+++ b/fs/jbd2/transaction.c
@@ -639,6 +639,7 @@ do_get_write_access(handle_t *handle, struct journal_head *jh,
int error;
char *frozen_buffer = NULL;
int need_copy = 0;
+ unsigned long start_lock, time_lock;
if (is_handle_aborted(handle))
return -EROFS;
@@ -654,9 +655,16 @@ repeat:
/* @@@ Need to check for errors here at some point. */
+ start_lock = jiffies;
lock_buffer(bh);
jbd_lock_bh_state(bh);
+ /* If it takes too long to lock the buffer, trace it */
+ time_lock = jbd2_time_diff(start_lock, jiffies);
+ if (time_lock > HZ/10)
+ trace_jbd2_lock_buffer_stall(bh->b_bdev->bd_dev,
+ jiffies_to_msecs(time_lock));
+
/* We now hold the buffer lock so it is safe to query the buffer
* state. Is the buffer dirty?
*