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, 3 insertions, 38 deletions

diff --git a/mm/slab.c b/mm/slab.c
index f40e5c95e11a..684ebe5b0c7a 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -1379,11 +1379,7 @@ static struct page *kmem_getpages(struct kmem_cache *cachep, gfp_t flags,
 		return NULL;
 	}
 
-	if (charge_slab_page(page, flags, cachep->gfporder, cachep)) {
-		__free_pages(page, cachep->gfporder);
-		return NULL;
-	}
-
+	charge_slab_page(page, flags, cachep->gfporder, cachep);
 	__SetPageSlab(page);
 	/* Record if ALLOC_NO_WATERMARKS was set when allocating the slab */
 	if (sk_memalloc_socks() && page_is_pfmemalloc(page))
@@ -3799,8 +3795,8 @@ fail:
 }
 
 /* Always called with the slab_mutex held */
-static int __do_tune_cpucache(struct kmem_cache *cachep, int limit,
-				int batchcount, int shared, gfp_t gfp)
+static int do_tune_cpucache(struct kmem_cache *cachep, int limit,
+			    int batchcount, int shared, gfp_t gfp)
 {
 	struct array_cache __percpu *cpu_cache, *prev;
 	int cpu;
@@ -3845,30 +3841,6 @@ setup_node:
 	return setup_kmem_cache_nodes(cachep, gfp);
 }
 
-static int do_tune_cpucache(struct kmem_cache *cachep, int limit,
-				int batchcount, int shared, gfp_t gfp)
-{
-	int ret;
-	struct kmem_cache *c;
-
-	ret = __do_tune_cpucache(cachep, limit, batchcount, shared, gfp);
-
-	if (slab_state < FULL)
-		return ret;
-
-	if ((ret < 0) || !is_root_cache(cachep))
-		return ret;
-
-	lockdep_assert_held(&slab_mutex);
-	c = memcg_cache(cachep);
-	if (c) {
-		/* return value determined by the root cache only */
-		__do_tune_cpucache(c, limit, batchcount, shared, gfp);
-	}
-
-	return ret;
-}
-
 /* Called with slab_mutex held always */
 static int enable_cpucache(struct kmem_cache *cachep, gfp_t gfp)
 {
@@ -3881,13 +3853,6 @@ static int enable_cpucache(struct kmem_cache *cachep, gfp_t gfp)
 	if (err)
 		goto end;
 
-	if (!is_root_cache(cachep)) {
-		struct kmem_cache *root = memcg_root_cache(cachep);
-		limit = root->limit;
-		shared = root->shared;
-		batchcount = root->batchcount;
-	}
-
 	if (limit && shared && batchcount)
 		goto skip_setup;
 	/*