[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <0919aaab-cc08-f86d-1f9a-8ddfeed7bb31@redhat.com>
Date: Wed, 12 May 2021 10:54:19 -0400
From: Waiman Long <llong@...hat.com>
To: Johannes Weiner <hannes@...xchg.org>,
Michal Hocko <mhocko@...nel.org>,
Vladimir Davydov <vdavydov.dev@...il.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Christoph Lameter <cl@...ux.com>,
Pekka Enberg <penberg@...nel.org>,
David Rientjes <rientjes@...gle.com>,
Joonsoo Kim <iamjoonsoo.kim@....com>,
Vlastimil Babka <vbabka@...e.cz>, Roman Gushchin <guro@...com>,
Shakeel Butt <shakeelb@...gle.com>
Cc: linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
linux-mm@...ck.org
Subject: Re: [PATCH v5 2/3] mm: memcg/slab: Create a new set of kmalloc-cg-<n>
caches
On 5/12/21 10:51 AM, 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.
>
> Signed-off-by: Waiman Long <longman@...hat.com>
> Suggested-by: Vlastimil Babka <vbabka@...e.cz>
> Reviewed-by: Shakeel Butt <shakeelb@...gle.com>
> Acked-by: Roman Gushchin <guro@...com>
> ---
> include/linux/slab.h | 42 +++++++++++++++++++++++++++++++++---------
> mm/slab_common.c | 25 +++++++++++++++++--------
> 2 files changed, 50 insertions(+), 17 deletions(-)
The following are the diff's from previous version. It turns out that
the previous patch doesn't work if CONFIG_ZONE_DMA isn't defined.
diff --git a/include/linux/slab.h b/include/linux/slab.h
index a51cad5f561c..aa7f6c222a60 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -312,16 +312,17 @@ static inline void __check_heap_object(const void
*ptr, un
signed long n,
*/
enum kmalloc_cache_type {
KMALLOC_NORMAL = 0,
-#ifdef CONFIG_MEMCG_KMEM
- KMALLOC_CGROUP,
-#else
+#ifndef CONFIG_ZONE_DMA
+ KMALLOC_DMA = KMALLOC_NORMAL,
+#endif
+#ifndef CONFIG_MEMCG_KMEM
KMALLOC_CGROUP = KMALLOC_NORMAL,
+#else
+ KMALLOC_CGROUP,
#endif
KMALLOC_RECLAIM,
#ifdef CONFIG_ZONE_DMA
KMALLOC_DMA,
-#else
- KMALLOC_DMA = KMALLOC_NORMAL,
#endif
NR_KMALLOC_TYPES
};
Cheers,
Longman
Powered by blists - more mailing lists