f2fs: fix a hungtask problem caused by congestion_wait

This patch fix hungtask problem which can be reproduced as follow:

Thread 0~3:
while true
do
        touch /xxx/test/file_xxx
done

Thread 4 write a new checkpoint every three seconds.

In the meantime, fio start 16 threads for randwrite.

With my debug info, cycles num will exceed 1000 in function
f2fs_sync_dirty_inodes, and most of cycle will be dropped
into congestion_wait() and sleep more than 20ms. Cycles num
reduced to 3 with this patch.

Signed-off-by: Yunlei He <heyunlei@huawei.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
index 502d7af..e5cf2ff 100644 (file)
--- a/fs/f2fs/checkpoint.c
+++ b/fs/f2fs/checkpoint.c
@@ -972,12 +972,10 @@ retry:
 
                iput(inode);
                /* We need to give cpu to another writers. */
-               if (ino == cur_ino) {
-                       congestion_wait(BLK_RW_ASYNC, HZ/50);
+               if (ino == cur_ino)
                        cond_resched();
-               } else {
+               else
                        ino = cur_ino;
-               }
        } else {
                /*
                 * We should submit bio, since it exists several