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Tue, 04 May 2021 18:56:02 -0700 (PDT) Received: from llong.remote.csb ([2601:191:8500:76c0::cdbc]) by smtp.gmail.com with ESMTPSA id o189sm12603642qkd.60.2021.05.04.18.56.00 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 04 May 2021 18:56:01 -0700 (PDT) From: Waiman Long X-Google-Original-From: Waiman Long Subject: Re: [PATCH v2 2/2] mm: memcg/slab: Create a new set of kmalloc-cg- caches To: Vlastimil Babka , 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: <20210504132350.4693-1-longman@redhat.com> <20210504132350.4693-3-longman@redhat.com> <3c952b24-94e4-3c54-b668-cac778ff5a77@suse.cz> Message-ID: <26ef8e5d-3a72-324f-4ef9-ead8c6251e70@redhat.com> Date: Tue, 4 May 2021 21:55:59 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.9.0 MIME-Version: 1.0 In-Reply-To: <3c952b24-94e4-3c54-b668-cac778ff5a77@suse.cz> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Authentication-Results: imf01.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=COprRlNY; spf=none (imf01.hostedemail.com: domain of llong@redhat.com has no SPF policy when checking 170.10.133.124) smtp.mailfrom=llong@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 25D2A500152F X-Stat-Signature: iub5ex5ocfdmds71m3smybid6nm53fub Received-SPF: none (redhat.com>: No applicable sender policy available) receiver=imf01; identity=mailfrom; envelope-from=""; helo=us-smtp-delivery-124.mimecast.com; client-ip=170.10.133.124 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1620179752-136717 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 5/4/21 12:01 PM, Vlastimil Babka wrote: > On 5/4/21 3:23 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 non-accounted objects only and a new set of >> kmalloc-cg- (KMALLOC_CGROUP) caches for accounted objects only. All >> the other caches can allow a mix of accounted and non-accounted 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. >> >> 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. > Great, thanks I hope there would be also benefits to objcg arrays not > created for all the normal caches anymore (possibly poorly used due to > mix of accounted and non-accounted objects in the same cache) and perhaps > it's possible for you to quantify the reduction of those? Right, I will update the commit log to mention that as well. Thanks! >> Suggested-by: Vlastimil Babka >> Signed-off-by: Waiman Long > ... > >> @@ -321,6 +328,14 @@ kmalloc_caches[NR_KMALLOC_TYPES][KMALLOC_SHIFT_HIGH + 1]; >> >> static __always_inline enum kmalloc_cache_type kmalloc_type(gfp_t flags) >> { >> +#ifdef CONFIG_MEMCG_KMEM >> + /* >> + * KMALLOC_CGROUP for non-reclaimable and non-DMA object with >> + * accounting enabled. >> + */ >> + if ((flags & (__GFP_DMA | __GFP_RECLAIMABLE | __GFP_ACCOUNT)) == __GFP_ACCOUNT) >> + return KMALLOC_CGROUP; >> +#endif > This function was designed so that KMALLOC_NORMAL would be the first tested and > returned possibility, as it's expected to be the most common. What about the > following on top? > > ----8<---- > diff --git a/include/linux/slab.h b/include/linux/slab.h > index fca03c22ea7c..418c5df0305b 100644 > --- a/include/linux/slab.h > +++ b/include/linux/slab.h > @@ -328,30 +328,40 @@ kmalloc_caches[NR_KMALLOC_TYPES][KMALLOC_SHIFT_HIGH + 1]; > > static __always_inline enum kmalloc_cache_type kmalloc_type(gfp_t flags) > { > -#ifdef CONFIG_MEMCG_KMEM > /* > - * KMALLOC_CGROUP for non-reclaimable and non-DMA object with > - * accounting enabled. > + * The most common case is KMALLOC_NORMAL, so test for it > + * with a single branch for all flags that might affect it > */ > - if ((flags & (__GFP_DMA | __GFP_RECLAIMABLE | __GFP_ACCOUNT)) == __GFP_ACCOUNT) > - return KMALLOC_CGROUP; > + if (likely((flags & (__GFP_RECLAIMABLE > +#ifdef CONFIG_MEMCG_KMEM > + | __GFP_ACCOUNT > #endif > #ifdef CONFIG_ZONE_DMA > - /* > - * The most common case is KMALLOC_NORMAL, so test for it > - * with a single branch for both flags. > - */ > - if (likely((flags & (__GFP_DMA | __GFP_RECLAIMABLE)) == 0)) > + | __GFP_DMA > +#endif > + )) == 0)) > return KMALLOC_NORMAL; > > +#ifdef CONFIG_MEMCG_KMEM > /* > - * At least one of the flags has to be set. If both are, __GFP_DMA > - * is more important. > + * KMALLOC_CGROUP for non-reclaimable and non-DMA object with > + * accounting enabled. > */ > - return flags & __GFP_DMA ? KMALLOC_DMA : KMALLOC_RECLAIM; > -#else > - return flags & __GFP_RECLAIMABLE ? KMALLOC_RECLAIM : KMALLOC_NORMAL; > + if ((flags & (__GFP_ACCOUNT | __GFP_RECLAIMABLE > +#ifdef CONFIG_ZONE_DMApropose this to the customer as proposing this will create a lot of confusion > + | __GFP_DMA > +#endif > + )) == __GFP_ACCOUNT) > + return KMALLOC_CGROUP; > #endif > + > +#ifdef CONFIG_ZONE_DMA > + if (flags & __GFP_DMA) > + return KMALLOC_DMA; > +#endif > + > + /* if we got here, it has to be __GFP_RECLAIMABLE */ > + return KMALLOC_RECLAIM; > } > > /* > OK, I will make KMALLOC_NORMAL the first in the test. However the proposed change is a bit hard to read, so I will probably change it a bit. Thanks, Longman