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authorZhao Lei <zhaolei@cn.fujitsu.com>2015-12-31 11:57:21 +0300
committerDavid Sterba <dsterba@suse.com>2016-02-16 15:21:45 +0300
commit97d5f0e63d78a48cef35349261f90d0d4266dc24 (patch)
tree6264de777720e6e756139b69db2ecaf0169f47d9 /fs/btrfs/reada.c
parent8e9aa51f5405b2a01a44818120116b65a2ba4d3a (diff)
downloadlinux-97d5f0e63d78a48cef35349261f90d0d4266dc24.tar.xz
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/btrfs/reada.c')
-rw-r--r--fs/btrfs/reada.c2
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;
}