Messages in this thread Patch in this message | | | Subject | [PATCH] Avoid useless inodes and dentries reclamation | From | Tim Chen <> | Date | Wed, 28 Aug 2013 14:52:12 -0700 |
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This patch detects that when free inodes and dentries are really low, their reclamation is skipped so we do not have to contend on the global sb_lock uselessly under memory pressure. Otherwise we create a log jam trying to acquire the sb_lock in prune_super(), with little or no freed memory to show for the effort.
The profile below shows a multi-threaded large file read exerting pressure on memory with page cache usage. It is dominated by the sb_lock contention in the cpu cycles profile. The patch eliminates the sb_lock contention almost entirely for prune_super().
43.94% usemem [kernel.kallsyms] [k] _raw_spin_lock | --- _raw_spin_lock | |--32.44%-- grab_super_passive | prune_super | shrink_slab | do_try_to_free_pages | try_to_free_pages | __alloc_pages_nodemask | alloc_pages_current | |--32.18%-- put_super | drop_super | prune_super | shrink_slab | do_try_to_free_pages | try_to_free_pages | __alloc_pages_nodemask | alloc_pages_current
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com> --- fs/super.c | 8 ++++++++ 1 file changed, 8 insertions(+)
diff --git a/fs/super.c b/fs/super.c index 68307c0..70fa26c 100644 --- a/fs/super.c +++ b/fs/super.c @@ -53,6 +53,7 @@ static char *sb_writers_name[SB_FREEZE_LEVELS] = { * shrinker path and that leads to deadlock on the shrinker_rwsem. Hence we * take a passive reference to the superblock to avoid this from occurring. */ +#define SB_CACHE_LOW 5 static int prune_super(struct shrinker *shrink, struct shrink_control *sc) { struct super_block *sb; @@ -68,6 +69,13 @@ static int prune_super(struct shrinker *shrink, struct shrink_control *sc) if (sc->nr_to_scan && !(sc->gfp_mask & __GFP_FS)) return -1; + /* + * Don't prune if we have few cached objects to reclaim to + * avoid useless sb_lock contention + */ + if ((sb->s_nr_dentry_unused + sb->s_nr_inodes_unused) <= SB_CACHE_LOW) + return -1; + if (!grab_super_passive(sb)) return -1; -- 1.7.11.7
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