From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B4D4FC433B4 for ; Thu, 6 May 2021 16:00:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6AC27610E9 for ; Thu, 6 May 2021 16:00:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235658AbhEFQBS (ORCPT ); Thu, 6 May 2021 12:01:18 -0400 Received: from mx2.suse.de ([195.135.220.15]:58278 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235321AbhEFQBQ (ORCPT ); Thu, 6 May 2021 12:01:16 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id F1736B004; Thu, 6 May 2021 16:00:16 +0000 (UTC) Subject: Re: [PATCH v4 2/3] mm: memcg/slab: Create a new set of kmalloc-cg- caches To: Waiman Long , Johannes Weiner , Michal Hocko , Vladimir Davydov , Andrew Morton , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Roman Gushchin , Shakeel Butt Cc: linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-mm@kvack.org References: <20210505200610.13943-1-longman@redhat.com> <20210505200610.13943-3-longman@redhat.com> From: Vlastimil Babka Message-ID: <3344a04c-0cff-b997-f357-2ffc8e3de242@suse.cz> Date: Thu, 6 May 2021 18:00:16 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.10.0 MIME-Version: 1.0 In-Reply-To: <20210505200610.13943-3-longman@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/5/21 10:06 PM, 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- caches > (KMALLOC_NORMAL) into two separate sets - a new set of kmalloc- > (KMALLOC_NORMAL) caches for unaccounted objects only and a new set of > kmalloc-cg- (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 > Signed-off-by: Waiman Long > Reviewed-by: Shakeel Butt Reviewed-by: Vlastimil Babka I still believe the cgroup.memory=nokmem parameter should be respected, otherwise the caches are not only created, but also used. I offer this followup for squashing into your patch if you and Andrew agree: ----8<---- >From c87378d437d9a59b8757033485431b4721c74173 Mon Sep 17 00:00:00 2001 From: Vlastimil Babka Date: Thu, 6 May 2021 17:53:21 +0200 Subject: [PATCH] mm: memcg/slab: don't create kmalloc-cg caches with cgroup.memory=nokmem The caches should not be created when kmemcg is disabled on boot, otherwise they are also filled by kmalloc(__GFP_ACCOUNT) allocations. When booted with cgroup.memory=nokmem, link the kmalloc_caches[KMALLOC_CGROUP] entries to KMALLOC_NORMAL entries instead. Signed-off-by: Vlastimil Babka --- mm/internal.h | 5 +++++ mm/memcontrol.c | 2 +- mm/slab_common.c | 9 +++++++-- 3 files changed, 13 insertions(+), 3 deletions(-) diff --git a/mm/internal.h b/mm/internal.h index ef5f336f59bd..b2d60b3403c7 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -135,6 +135,11 @@ extern void putback_lru_page(struct page *page); */ extern pmd_t *mm_find_pmd(struct mm_struct *mm, unsigned long address); +/* + * in mm/memcontrol.c: + */ +extern bool cgroup_memory_nokmem; + /* * in mm/page_alloc.c */ diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 5e3b4f23b830..b9ec01f2b4f6 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -83,7 +83,7 @@ DEFINE_PER_CPU(struct mem_cgroup *, int_active_memcg); static bool cgroup_memory_nosocket; /* Kernel memory accounting disabled? */ -static bool cgroup_memory_nokmem; +bool cgroup_memory_nokmem; /* Whether the swap controller is active */ #ifdef CONFIG_MEMCG_SWAP diff --git a/mm/slab_common.c b/mm/slab_common.c index bbaf41a7c77e..363f90215401 100644 --- a/mm/slab_common.c +++ b/mm/slab_common.c @@ -832,10 +832,15 @@ void __init setup_kmalloc_cache_index_table(void) static void __init new_kmalloc_cache(int idx, enum kmalloc_cache_type type, slab_flags_t flags) { - if (type == KMALLOC_RECLAIM) + if (type == KMALLOC_RECLAIM) { flags |= SLAB_RECLAIM_ACCOUNT; - else if (IS_ENABLED(CONFIG_MEMCG_KMEM) && (type == KMALLOC_CGROUP)) + } else if (IS_ENABLED(CONFIG_MEMCG_KMEM) && (type == KMALLOC_CGROUP)) { + if (cgroup_memory_nokmem) { + kmalloc_caches[type][idx] = kmalloc_caches[KMALLOC_NORMAL][idx]; + return; + } flags |= SLAB_ACCOUNT; + } kmalloc_caches[type][idx] = create_kmalloc_cache( kmalloc_info[idx].name[type], -- 2.31.1