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From: Kirill Tkhai <ktkhai@virtuozzo.com>
To: vdavydov.dev@gmail.com, shakeelb@google.com,
	viro@zeniv.linux.org.uk, hannes@cmpxchg.org, mhocko@kernel.org,
	tglx@linutronix.de, pombredanne@nexb.com,
	stummala@codeaurora.org, gregkh@linuxfoundation.org,
	sfr@canb.auug.org.au, guro@fb.com, mka@chromium.org,
	penguin-kernel@I-love.SAKURA.ne.jp, chris@chris-wilson.co.uk,
	longman@redhat.com, minchan@kernel.org, ying.huang@intel.com,
	mgorman@techsingularity.net, jbacik@fb.com, linux@roeck-us.net,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	willy@infradead.org, lirongqing@baidu.com,
	aryabinin@virtuozzo.com, akpm@linux-foundation.org,
	ktkhai@virtuozzo.com
Subject: [PATCH v8 16/17] mm: Add SHRINK_EMPTY shrinker methods return value
Date: Tue, 03 Jul 2018 18:11:35 +0300
Message-ID: <153063069574.1818.11037751256699341813.stgit@localhost.localdomain> (raw)
In-Reply-To: <153063036670.1818.16010062622751502.stgit@localhost.localdomain>

We need to differ 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.

Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Acked-by: Vladimir Davydov <vdavydov.dev@gmail.com>
Tested-by: Shakeel Butt <shakeelb@google.com>
---
 fs/super.c               |    3 +++
 include/linux/shrinker.h |    7 +++++--
 mm/vmscan.c              |   12 +++++++++---
 mm/workingset.c          |    3 +++
 4 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/fs/super.c b/fs/super.c
index f858178f74fe..00b0154487df 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -146,6 +146,9 @@ static unsigned long super_cache_count(struct shrinker *shrink,
 	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;
 }
diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
index 7ca9c18cf130..b154fd2b084c 100644
--- a/include/linux/shrinker.h
+++ b/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.
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 39f0ba75f7f7..96279b5f1f6d 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -453,8 +453,8 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
 	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
@@ -597,6 +597,8 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
 			continue;
 
 		ret = do_shrink_slab(&sc, shrinker, priority);
+		if (ret == SHRINK_EMPTY)
+			ret = 0;
 		freed += ret;
 
 		if (rwsem_is_contended(&shrinker_rwsem)) {
@@ -642,6 +644,7 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
 {
 	struct shrinker *shrinker;
 	unsigned long freed = 0;
+	int ret;
 
 	if (!mem_cgroup_is_root(memcg))
 		return shrink_slab_memcg(gfp_mask, nid, memcg, priority);
@@ -659,7 +662,10 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
 		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
diff --git a/mm/workingset.c b/mm/workingset.c
index a682306db49b..8350b6ec76ce 100644
--- a/mm/workingset.c
+++ b/mm/workingset.c
@@ -397,6 +397,9 @@ static unsigned long count_shadow_nodes(struct shrinker *shrinker,
 	}
 	max_nodes = cache >> (XA_CHUNK_SHIFT - 3);
 
+	if (!nodes)
+		return SHRINK_EMPTY;
+
 	if (nodes <= max_nodes)
 		return 0;
 	return nodes - max_nodes;

  parent reply index

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-07-03 15:08 [PATCH v8 00/17] Improve shrink_slab() scalability (old complexity was O(n^2), new is O(n)) Kirill Tkhai
2018-07-03 15:08 ` [PATCH v8 01/17] list_lru: Combine code under the same define Kirill Tkhai
2018-07-03 15:08 ` [PATCH v8 02/17] mm: Introduce CONFIG_MEMCG_KMEM as combination of CONFIG_MEMCG && !CONFIG_SLOB Kirill Tkhai
2018-07-03 15:09 ` [PATCH v8 03/17] mm: Assign id to every memcg-aware shrinker Kirill Tkhai
2018-07-03 15:27   ` Matthew Wilcox
2018-07-03 15:46     ` Shakeel Butt
2018-07-03 16:17       ` Kirill Tkhai
2018-07-03 17:00         ` Shakeel Butt
2018-07-03 17:32           ` Kirill Tkhai
2018-07-12 11:13             ` Kirill Tkhai
2018-07-12 11:19               ` Kirill Tkhai
2018-07-03 17:47       ` Matthew Wilcox
2018-07-03 20:39         ` Al Viro
2018-07-03 15:46     ` Kirill Tkhai
2018-07-03 17:58       ` Matthew Wilcox
2018-07-03 19:12         ` Kirill Tkhai
2018-07-03 19:19           ` Shakeel Butt
2018-07-03 19:25             ` Matthew Wilcox
2018-07-03 19:54               ` Shakeel Butt
2018-07-03 15:09 ` [PATCH v8 04/17] memcg: Move up for_each_mem_cgroup{, _tree} defines Kirill Tkhai
2018-07-03 15:09 ` [PATCH v8 05/17] mm: Assign memcg-aware shrinkers bitmap to memcg Kirill Tkhai
2018-07-03 20:50   ` Andrew Morton
2018-07-04 15:51     ` Kirill Tkhai
2018-07-05 22:10       ` Andrew Morton
2018-07-06 17:50         ` Vladimir Davydov
2018-07-05 22:50     ` Matthew Wilcox
2018-07-06 17:30     ` Vladimir Davydov
2018-07-03 15:09 ` [PATCH v8 06/17] mm: Refactoring in workingset_init() Kirill Tkhai
2018-07-03 15:09 ` [PATCH v8 07/17] fs: Refactoring in alloc_super() Kirill Tkhai
2018-07-03 15:09 ` [PATCH v8 08/17] fs: Propagate shrinker::id to list_lru Kirill Tkhai
2018-07-03 15:10 ` [PATCH v8 09/17] list_lru: Add memcg argument to list_lru_from_kmem() Kirill Tkhai
2018-07-03 15:10 ` [PATCH v8 10/17] list_lru: Pass dst_memcg argument to memcg_drain_list_lru_node() Kirill Tkhai
2018-07-03 15:10 ` [PATCH v8 11/17] list_lru: Pass lru " Kirill Tkhai
2018-07-03 15:10 ` [PATCH v8 12/17] mm: Export mem_cgroup_is_root() Kirill Tkhai
2018-07-03 15:10 ` [PATCH v8 13/17] mm: Set bit in memcg shrinker bitmap on first list_lru item apearance Kirill Tkhai
2018-07-03 20:54   ` Andrew Morton
2018-07-03 15:11 ` [PATCH v8 14/17] mm: Iterate only over charged shrinkers during memcg shrink_slab() Kirill Tkhai
2018-07-03 20:58   ` Andrew Morton
2018-07-04 14:56     ` Kirill Tkhai
2018-07-03 15:11 ` [PATCH v8 15/17] mm: Generalize shrink_slab() calls in shrink_node() Kirill Tkhai
2018-07-03 15:11 ` Kirill Tkhai [this message]
2018-07-03 15:11 ` [PATCH v8 17/17] mm: Clear shrinker bit if there are no objects related to memcg Kirill Tkhai

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