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authorKonstantin Khlebnikov <khlebnikov@yandex-team.ru>2015-02-19 20:19:35 +0300
committerAl Viro <viro@zeniv.linux.org.uk>2015-02-22 19:38:42 +0300
commiteb6ef3df4faa5424cf2a24b4e4f3eeceb1482a8e (patch)
tree760db5df872be2122597841c33479c41cf2d7194 /fs/fs-writeback.c
parent54f2a2f42759b11ada761013a12f0e743702219a (diff)
downloadlinux-eb6ef3df4faa5424cf2a24b4e4f3eeceb1482a8e.tar.xz
trylock_super(): replacement for grab_super_passive()
I've noticed significant locking contention in memory reclaimer around sb_lock inside grab_super_passive(). Grab_super_passive() is called from two places: in icache/dcache shrinkers (function super_cache_scan) and from writeback (function __writeback_inodes_wb). Both are required for progress in memory allocator. Grab_super_passive() acquires sb_lock to increment sb->s_count and check sb->s_instances. It seems sb->s_umount locked for read is enough here: super-block deactivation always runs under sb->s_umount locked for write. Protecting super-block itself isn't a problem: in super_cache_scan() sb is protected by shrinker_rwsem: it cannot be freed if its slab shrinkers are still active. Inside writeback super-block comes from inode from bdi writeback list under wb->list_lock. This patch removes locking sb_lock and checks s_instances under s_umount: generic_shutdown_super() unlinks it under sb->s_umount locked for write. New variant is called trylock_super() and since it only locks semaphore, callers must call up_read(&sb->s_umount) instead of drop_super(sb) when they're done. Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'fs/fs-writeback.c')
-rw-r--r--fs/fs-writeback.c6
1 files changed, 3 insertions, 3 deletions
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 073657f755d4..e907052eeadb 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -769,9 +769,9 @@ static long __writeback_inodes_wb(struct bdi_writeback *wb,
struct inode *inode = wb_inode(wb->b_io.prev);
struct super_block *sb = inode->i_sb;
- if (!grab_super_passive(sb)) {
+ if (!trylock_super(sb)) {
/*
- * grab_super_passive() may fail consistently due to
+ * trylock_super() may fail consistently due to
* s_umount being grabbed by someone else. Don't use
* requeue_io() to avoid busy retrying the inode/sb.
*/
@@ -779,7 +779,7 @@ static long __writeback_inodes_wb(struct bdi_writeback *wb,
continue;
}
wrote += writeback_sb_inodes(sb, wb, work);
- drop_super(sb);
+ up_read(&sb->s_umount);
/* refer to the same tests at the end of writeback_sb_inodes */
if (wrote) {