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| author | Zhao Lei <zhaolei@cn.fujitsu.com> | 2015-12-31 16:57:21 +0800 |
|---|---|---|
| committer | David Sterba <dsterba@suse.com> | 2016-02-16 13:21:45 +0100 |
| commit | 97d5f0e63d78a48cef35349261f90d0d4266dc24 (patch) | |
| tree | 6264de777720e6e756139b69db2ecaf0169f47d9 /fs | |
| parent | 8e9aa51f5405b2a01a44818120116b65a2ba4d3a (diff) | |
| download | linux-rt-97d5f0e63d78a48cef35349261f90d0d4266dc24.tar.gz | |
btrfs: reada: Avoid many times of empty loop
We can see following loop(10000 times) in trace_log:
[ 75.416137] ZL_DEBUG: reada_start_machine_dev:730: pid=771 comm=kworker/u2:3 re->ref_cnt ffff88003741e0c0 1 -> 2
[ 75.417413] ZL_DEBUG: reada_extent_put:524: pid=771 comm=kworker/u2:3 re = ffff88003741e0c0, refcnt = 2 -> 1
[ 75.418611] ZL_DEBUG: __readahead_hook:129: pid=771 comm=kworker/u2:3 re->ref_cnt ffff88003741e0c0 1 -> 2
[ 75.419793] ZL_DEBUG: reada_extent_put:524: pid=771 comm=kworker/u2:3 re = ffff88003741e0c0, refcnt = 2 -> 1
[ 75.421016] ZL_DEBUG: reada_start_machine_dev:730: pid=771 comm=kworker/u2:3 re->ref_cnt ffff88003741e0c0 1 -> 2
[ 75.422324] ZL_DEBUG: reada_extent_put:524: pid=771 comm=kworker/u2:3 re = ffff88003741e0c0, refcnt = 2 -> 1
[ 75.423661] ZL_DEBUG: __readahead_hook:129: pid=771 comm=kworker/u2:3 re->ref_cnt ffff88003741e0c0 1 -> 2
[ 75.424882] ZL_DEBUG: reada_extent_put:524: pid=771 comm=kworker/u2:3 re = ffff88003741e0c0, refcnt = 2 -> 1
...(10000 times)
[ 124.101672] ZL_DEBUG: reada_start_machine_dev:730: pid=771 comm=kworker/u2:3 re->ref_cnt ffff88003741e0c0 1 -> 2
[ 124.102850] ZL_DEBUG: reada_extent_put:524: pid=771 comm=kworker/u2:3 re = ffff88003741e0c0, refcnt = 2 -> 1
[ 124.104008] ZL_DEBUG: __readahead_hook:129: pid=771 comm=kworker/u2:3 re->ref_cnt ffff88003741e0c0 1 -> 2
[ 124.105121] ZL_DEBUG: reada_extent_put:524: pid=771 comm=kworker/u2:3 re = ffff88003741e0c0, refcnt = 2 -> 1
Reason:
If more than one user trigger reada in same extent, the first task
finished setting of reada data struct and call reada_start_machine()
to start, and the second task only add a ref_count but have not
add reada_extctl struct completely, the reada_extent can not finished
all jobs, and will be selected in __reada_start_machine() for 10000
times(total times in __reada_start_machine()).
Fix:
For a reada_extent without job, we don't need to run it, just return
0 to let caller break.
Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Diffstat (limited to 'fs')
| -rw-r--r-- | fs/btrfs/reada.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/fs/btrfs/reada.c b/fs/btrfs/reada.c index 7e5d4ac800d9..f0cf5f3b865a 100644 --- a/fs/btrfs/reada.c +++ b/fs/btrfs/reada.c @@ -708,7 +708,7 @@ static int reada_start_machine_dev(struct btrfs_fs_info *fs_info, logical = re->logical; spin_lock(&re->lock); - if (re->scheduled_for == NULL) { + if (!re->scheduled_for && !list_empty(&re->extctl)) { re->scheduled_for = dev; need_kick = 1; } |