[PATCH v4 3/3] mm: memcg/slab: Disable cache merging for KMALLOC_NORMAL caches

From: Waiman Long <longman@redhat.com>
To: Johannes Weiner <hannes@cmpxchg.org>,
	Michal Hocko <mhocko@kernel.org>,
	Vladimir Davydov <vdavydov.dev@gmail.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Christoph Lameter <cl@linux.com>,
	Pekka Enberg <penberg@kernel.org>,
	David Rientjes <rientjes@google.com>,
	Joonsoo Kim <iamjoonsoo.kim@lge.com>,
	Vlastimil Babka <vbabka@suse.cz>, Roman Gushchin <guro@fb.com>,
	Shakeel Butt <shakeelb@google.com>
Cc: linux-kernel@vger.kernel.org, cgroups@vger.kernel.org,
	linux-mm@kvack.org, Waiman Long <longman@redhat.com>
Subject: [PATCH v4 3/3] mm: memcg/slab: Disable cache merging for KMALLOC_NORMAL caches
Date: Wed,  5 May 2021 16:06:10 -0400	[thread overview]
Message-ID: <20210505200610.13943-4-longman@redhat.com> (raw)
In-Reply-To: <20210505200610.13943-1-longman@redhat.com>

The KMALLOC_NORMAL (kmalloc-<n>) caches are for unaccounted objects only
when CONFIG_MEMCG_KMEM is enabled. To make sure that this condition
remains true, we will have to prevent KMALOC_NORMAL caches to merge
with other kmem caches. This is now done by setting its refcount to -1
right after its creation.

Suggested-by: Roman Gushchin <guro@fb.com>
Signed-off-by: Waiman Long <longman@redhat.com>
---
 mm/slab_common.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/mm/slab_common.c b/mm/slab_common.c
index bbaf41a7c77e..a0ff8e1d8b67 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -841,6 +841,13 @@ new_kmalloc_cache(int idx, enum kmalloc_cache_type type, slab_flags_t flags)
 					kmalloc_info[idx].name[type],
 					kmalloc_info[idx].size, flags, 0,
 					kmalloc_info[idx].size);
+
+	/*
+	 * If CONFIG_MEMCG_KMEM is enabled, disable cache merging for
+	 * KMALLOC_NORMAL caches.
+	 */
+	if (IS_ENABLED(CONFIG_MEMCG_KMEM) && (type == KMALLOC_NORMAL))
+		kmalloc_caches[type][idx]->refcount = -1;
 }
 
 /*
-- 
2.18.1

