From: Roman Gushchin <guro@fb.com>
To: Waiman Long <longman@redhat.com>
Cc: 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>,
Shakeel Butt <shakeelb@google.com>,
<linux-kernel@vger.kernel.org>, <cgroups@vger.kernel.org>,
<linux-mm@kvack.org>
Subject: Re: [PATCH v4 2/3] mm: memcg/slab: Create a new set of kmalloc-cg-<n> caches
Date: Wed, 5 May 2021 13:37:27 -0700 [thread overview]
Message-ID: <YJMCB/g8YctqQmlE@carbon.dhcp.thefacebook.com> (raw)
In-Reply-To: <20210505200610.13943-3-longman@redhat.com>
On Wed, May 05, 2021 at 04:06:09PM -0400, Waiman Long wrote:
> There are currently two problems in the way the objcg pointer array
> (memcg_data) in the page structure is being allocated and freed.
>
> On its allocation, it is possible that the allocated objcg pointer
> array comes from the same slab that requires memory accounting. If this
> happens, the slab will never become empty again as there is at least
> one object left (the obj_cgroup array) in the slab.
>
> When it is freed, the objcg pointer array object may be the last one
> in its slab and hence causes kfree() to be called again. With the
> right workload, the slab cache may be set up in a way that allows the
> recursive kfree() calling loop to nest deep enough to cause a kernel
> stack overflow and panic the system.
>
> One way to solve this problem is to split the kmalloc-<n> caches
> (KMALLOC_NORMAL) into two separate sets - a new set of kmalloc-<n>
> (KMALLOC_NORMAL) caches for unaccounted objects only and a new set of
> kmalloc-cg-<n> (KMALLOC_CGROUP) caches for accounted objects only. All
> the other caches can still allow a mix of accounted and unaccounted
> objects.
>
> With this change, all the objcg pointer array objects will come from
> KMALLOC_NORMAL caches which won't have their objcg pointer arrays. So
> both the recursive kfree() problem and non-freeable slab problem are
> gone.
>
> Since both the KMALLOC_NORMAL and KMALLOC_CGROUP caches no longer have
> mixed accounted and unaccounted objects, this will slightly reduce the
> number of objcg pointer arrays that need to be allocated and save a bit
> of memory. On the other hand, creating a new set of kmalloc caches does
> have the effect of reducing cache utilization. So it is properly a wash.
>
> The new KMALLOC_CGROUP is added between KMALLOC_NORMAL and
> KMALLOC_RECLAIM so that the first for loop in create_kmalloc_caches()
> will include the newly added caches without change.
>
> Suggested-by: Vlastimil Babka <vbabka@suse.cz>
> Signed-off-by: Waiman Long <longman@redhat.com>
> Reviewed-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Roman Gushchin <guro@fb.com>
next prev parent reply other threads:[~2021-05-05 20:37 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-05 20:06 [PATCH v4 0/3] mm: memcg/slab: Fix objcg pointer array handling problem Waiman Long
2021-05-05 20:06 ` [PATCH v4 1/3] mm: memcg/slab: Properly set up gfp flags for objcg pointer array Waiman Long
2021-05-05 20:35 ` Roman Gushchin
2021-05-06 15:37 ` Vlastimil Babka
2021-05-05 20:06 ` [PATCH v4 2/3] mm: memcg/slab: Create a new set of kmalloc-cg-<n> caches Waiman Long
2021-05-05 20:37 ` Roman Gushchin [this message]
2021-05-05 21:41 ` Vlastimil Babka
2021-05-05 23:19 ` Waiman Long
2021-05-06 16:00 ` Vlastimil Babka
2021-05-06 16:07 ` Shakeel Butt
2021-05-06 19:30 ` Roman Gushchin
2021-05-07 18:45 ` Waiman Long
2021-05-05 20:06 ` [PATCH v4 3/3] mm: memcg/slab: Disable cache merging for KMALLOC_NORMAL caches Waiman Long
2021-05-05 20:38 ` Roman Gushchin
2021-05-05 20:39 ` Shakeel Butt
2021-05-06 16:02 ` Vlastimil Babka
2021-05-12 14:51 ` [PATCH v5 2/3] mm: memcg/slab: Create a new set of kmalloc-cg-<n> caches Waiman Long
2021-05-12 14:54 ` Waiman Long
2021-05-13 0:32 ` Andrew Morton
2021-05-13 8:40 ` Vlastimil Babka
2021-05-13 16:22 ` Waiman Long
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