From: Kirill Tkhai <ktkhai@xxxxxxxxxxxxx> Subject: mm: add SHRINK_EMPTY shrinker methods return value We need to distinguish the situations when shrinker has very small amount of objects (see vfs_pressure_ratio() called from super_cache_count()), and when it has no objects at all. Currently, in the both of these cases, shrinker::count_objects() returns 0. The patch introduces new SHRINK_EMPTY return value, which will be used for "no objects at all" case. It's is a refactoring mostly, as SHRINK_EMPTY is replaced by 0 by all callers of do_shrink_slab() in this patch, and all the magic will happen in further. Link: http://lkml.kernel.org/r/153063069574.1818.11037751256699341813.stgit@localhost.localdomain Signed-off-by: Kirill Tkhai <ktkhai@xxxxxxxxxxxxx> Acked-by: Vladimir Davydov <vdavydov.dev@xxxxxxxxx> Tested-by: Shakeel Butt <shakeelb@xxxxxxxxxx> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx> Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx> Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> Cc: Guenter Roeck <linux@xxxxxxxxxxxx> Cc: "Huang, Ying" <ying.huang@xxxxxxxxx> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> Cc: Josef Bacik <jbacik@xxxxxx> Cc: Li RongQing <lirongqing@xxxxxxxxx> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> Cc: Matthias Kaehlcke <mka@xxxxxxxxxxxx> Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxxxx> Cc: Minchan Kim <minchan@xxxxxxxxxx> Cc: Philippe Ombredanne <pombredanne@xxxxxxxx> Cc: Roman Gushchin <guro@xxxxxx> Cc: Sahitya Tummala <stummala@xxxxxxxxxxxxxx> Cc: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx> Cc: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Waiman Long <longman@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- fs/super.c | 3 +++ include/linux/shrinker.h | 7 +++++-- mm/vmscan.c | 12 +++++++++--- mm/workingset.c | 3 +++ 4 files changed, 20 insertions(+), 5 deletions(-) --- a/fs/super.c~mm-add-shrink_empty-shrinker-methods-return-value +++ a/fs/super.c @@ -144,6 +144,9 @@ static unsigned long super_cache_count(s total_objects += list_lru_shrink_count(&sb->s_dentry_lru, sc); total_objects += list_lru_shrink_count(&sb->s_inode_lru, sc); + if (!total_objects) + return SHRINK_EMPTY; + total_objects = vfs_pressure_ratio(total_objects); return total_objects; } --- a/include/linux/shrinker.h~mm-add-shrink_empty-shrinker-methods-return-value +++ a/include/linux/shrinker.h @@ -34,12 +34,15 @@ struct shrink_control { }; #define SHRINK_STOP (~0UL) +#define SHRINK_EMPTY (~0UL - 1) /* * A callback you can register to apply pressure to ageable caches. * * @count_objects should return the number of freeable items in the cache. If - * there are no objects to free or the number of freeable items cannot be - * determined, it should return 0. No deadlock checks should be done during the + * there are no objects to free, it should return SHRINK_EMPTY, while 0 is + * returned in cases of the number of freeable items cannot be determined + * or shrinker should skip this cache for this time (e.g., their number + * is below shrinkable limit). No deadlock checks should be done during the * count callback - the shrinker relies on aggregating scan counts that couldn't * be executed due to potential deadlocks to be run at a later call when the * deadlock condition is no longer pending. --- a/mm/vmscan.c~mm-add-shrink_empty-shrinker-methods-return-value +++ a/mm/vmscan.c @@ -456,8 +456,8 @@ static unsigned long do_shrink_slab(stru long scanned = 0, next_deferred; freeable = shrinker->count_objects(shrinker, shrinkctl); - if (freeable == 0) - return 0; + if (freeable == 0 || freeable == SHRINK_EMPTY) + return freeable; /* * copy the current shrinker scan count into a local variable @@ -596,6 +596,8 @@ static unsigned long shrink_slab_memcg(g continue; ret = do_shrink_slab(&sc, shrinker, priority); + if (ret == SHRINK_EMPTY) + ret = 0; freed += ret; if (rwsem_is_contended(&shrinker_rwsem)) { @@ -641,6 +643,7 @@ static unsigned long shrink_slab(gfp_t g { struct shrinker *shrinker; unsigned long freed = 0; + int ret; if (!mem_cgroup_is_root(memcg)) return shrink_slab_memcg(gfp_mask, nid, memcg, priority); @@ -658,7 +661,10 @@ static unsigned long shrink_slab(gfp_t g if (!(shrinker->flags & SHRINKER_NUMA_AWARE)) sc.nid = 0; - freed += do_shrink_slab(&sc, shrinker, priority); + ret = do_shrink_slab(&sc, shrinker, priority); + if (ret == SHRINK_EMPTY) + ret = 0; + freed += ret; /* * Bail out if someone want to register a new shrinker to * prevent the regsitration from being stalled for long periods --- a/mm/workingset.c~mm-add-shrink_empty-shrinker-methods-return-value +++ a/mm/workingset.c @@ -399,6 +399,9 @@ static unsigned long count_shadow_nodes( } max_nodes = cache >> (RADIX_TREE_MAP_SHIFT - 3); + if (!nodes) + return SHRINK_EMPTY; + if (nodes <= max_nodes) return 0; return nodes - max_nodes; _
