From eb6ef3df4faa5424cf2a24b4e4f3eeceb1482a8e Mon Sep 17 00:00:00 2001 From: Konstantin Khlebnikov Date: Thu, 19 Feb 2015 20:19:35 +0300 Subject: 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 Signed-off-by: Al Viro --- fs/fs-writeback.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) (limited to 'fs/fs-writeback.c') 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) { -- cgit v1.2.3