mm: memcg/slab: use a single set of kmem_caches for all allocations

Instead of having two sets of kmem_caches: one for system-wide and
non-accounted allocations and the second one shared by all accounted
allocations, we can use just one.

The idea is simple: space for obj_cgroup metadata can be allocated on
demand and filled only for accounted allocations.

It allows to remove a bunch of code which is required to handle kmem_cache
clones for accounted allocations.  There is no more need to create them,
accumulate statistics, propagate attributes, etc.  It's a quite
significant simplification.

Also, because the total number of slab_caches is reduced almost twice (not
all kmem_caches have a memcg clone), some additional memory savings are
expected.  On my devvm it additionally saves about 3.5% of slab memory.

[guro@fb.com: fix build on MIPS]
  Link: http://lkml.kernel.org/r/20200717214810.3733082-1-guro@fb.com

Suggested-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Roman Gushchin <guro@fb.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Naresh Kamboju <naresh.kamboju@linaro.org>
Link: http://lkml.kernel.org/r/20200623174037.3951353-18-guro@fb.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 24 insertions, 1 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index a8113b77b23a..473f9b91d51f 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2800,6 +2800,26 @@ static void commit_charge(struct page *page, struct mem_cgroup *memcg)
 }
 
 #ifdef CONFIG_MEMCG_KMEM
+int memcg_alloc_page_obj_cgroups(struct page *page, struct kmem_cache *s,
+				 gfp_t gfp)
+{
+	unsigned int objects = objs_per_slab_page(s, page);
+	void *vec;
+
+	vec = kcalloc_node(objects, sizeof(struct obj_cgroup *), gfp,
+			   page_to_nid(page));
+	if (!vec)
+		return -ENOMEM;
+
+	if (cmpxchg(&page->obj_cgroups, NULL,
+		    (struct obj_cgroup **) ((unsigned long)vec | 0x1UL)))
+		kfree(vec);
+	else
+		kmemleak_not_leak(vec);
+
+	return 0;
+}
+
 /*
  * Returns a pointer to the memory cgroup to which the kernel object is charged.
  *
@@ -2826,7 +2846,10 @@ struct mem_cgroup *mem_cgroup_from_obj(void *p)
 
 		off = obj_to_index(page->slab_cache, page, p);
 		objcg = page_obj_cgroups(page)[off];
-		return obj_cgroup_memcg(objcg);
+		if (objcg)
+			return obj_cgroup_memcg(objcg);
+
+		return NULL;
 	}
 
 	/* All other pages use page->mem_cgroup */