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([2620:10d:c092:500::7:66a9]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-6005ac327d5sm7334255a12.63.2025.05.20.08.22.17 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 20 May 2025 08:22:17 -0700 (PDT) Message-ID: <64b19c8f-e02e-490b-b987-9a996f36be21@gmail.com> Date: Tue, 20 May 2025 16:22:16 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/2] mm: slub: only warn once when allocating slab obj extensions fails To: Shakeel Butt , surenb@google.com, Harry Yoo Cc: Andrew Morton , hannes@cmpxchg.org, vlad.wing@gmail.com, linux-mm@kvack.org, kent.overstreet@linux.dev, linux-kernel@vger.kernel.org, kernel-team@meta.com, vbabka@suse.cz, cl@gentwo.org, rientjes@google.com, roman.gushchin@linux.dev References: <20250520122547.1317050-1-usamaarif642@gmail.com> <20250520122547.1317050-2-usamaarif642@gmail.com> Content-Language: en-US From: Usama Arif In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 20/05/2025 15:18, Shakeel Butt wrote: > On Tue, May 20, 2025 at 02:42:09PM +0100, Usama Arif wrote: >> >> >> On 20/05/2025 14:34, Harry Yoo wrote: >>> On Tue, May 20, 2025 at 01:25:47PM +0100, Usama Arif wrote: >>>> In memory bound systems, a large number of warnings for failing this >>>> allocation repeatedly may mask any real issues in the system >>>> during memory pressure being reported in dmesg. Change this to >>>> WARN_ONCE. >>>> >>>> Signed-off-by: Usama Arif >>>> Reported-by: Vlad Poenaru >>>> Closes: https://lore.kernel.org/all/17fab2d6-5a74-4573-bcc3-b75951508f0a@gmail.com/ >>>> --- >>> >>> Hi, >>> >>> Please Cc SLAB ALLOCATOR folks in MAINTAINERS on patches that touch >>> slab code ;) >>> >> >> Thanks for adding them to CC! I was just thinking of this as a memory >> allocation profiling issue and added the maintainers for it, >> but should have added slab maintainers as well. >> >> >>>> mm/slub.c | 2 +- >>>> 1 file changed, 1 insertion(+), 1 deletion(-) >>>> >>>> diff --git a/mm/slub.c b/mm/slub.c >>>> index bf43c403ead2..97cb3d9e8d00 100644 >>>> --- a/mm/slub.c >>>> +++ b/mm/slub.c >>>> @@ -2102,7 +2102,7 @@ prepare_slab_obj_exts_hook(struct kmem_cache *s, gfp_t flags, void *p) >>>> >>>> slab = virt_to_slab(p); >>>> if (!slab_obj_exts(slab) && >>>> - WARN(alloc_slab_obj_exts(slab, s, flags, false), >>>> + WARN_ONCE(alloc_slab_obj_exts(slab, s, flags, false), >>>> "%s, %s: Failed to create slab extension vector!\n", >>>> __func__, s->name)) >>> >>> I think this should be pr_warn_once()? >>> I'm not sure why this was WARN() in the first place. >>> >> >> Isn't WARN_ONCE the same as pr_warn_once but with needing the condition >> of the first arg to be true? We only want to warn if alloc_slab_obj_exts >> returns non-zero. So WARN_ONCE should be ok? >> > > The difference is the impact on panic_on_warn users which are mostly > testing bots. This warning is not actionable, so I agree with Harry to > covert this to pr_warn_once(). > Sounds good! Will change it to below for the next revision. Will wait for the kvmalloc conversation to conclude before sending the next revision. diff --git a/mm/slub.c b/mm/slub.c index 08804d2f2ead..ab0b7ee87159 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -2101,11 +2101,13 @@ prepare_slab_obj_exts_hook(struct kmem_cache *s, gfp_t flags, void *p) return NULL; slab = virt_to_slab(p); - if (!slab_obj_exts(slab) && - WARN(alloc_slab_obj_exts(slab, s, flags, false), - "%s, %s: Failed to create slab extension vector!\n", - __func__, s->name)) - return NULL; + if (!slab_obj_exts(slab)) { + if(alloc_slab_obj_exts(slab, s, flags, false)) + pr_warn_once("%s, %s: Failed to create slab extension vector!\n", + __func__, s->name); + else + return NULL; + } return slab_obj_exts(slab) + obj_to_index(s, slab, p); }