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([2620:10d:c092:500::7:66a9]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-6004d4f5fe5sm7232206a12.7.2025.05.20.07.13.44 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 20 May 2025 07:13:45 -0700 (PDT) Message-ID: Date: Tue, 20 May 2025 15:13:44 +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 1/2] mm: slub: allocate slab object extensions non-contiguously From: Usama Arif To: Kent Overstreet Cc: Andrew Morton , surenb@google.com, hannes@cmpxchg.org, shakeel.butt@linux.dev, vlad.wing@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@meta.com References: <20250520122547.1317050-1-usamaarif642@gmail.com> <3divtzm4iapcxwbzxlmfmg3gus75n3rqh43vkjnog456jm2k34@f3rpzvcfk3p6> <6d015d91-e74c-48b3-8bc3-480980a74f9b@gmail.com> Content-Language: en-US In-Reply-To: <6d015d91-e74c-48b3-8bc3-480980a74f9b@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 20/05/2025 14:46, Usama Arif wrote: > > > On 20/05/2025 14:44, Kent Overstreet wrote: >> On Tue, May 20, 2025 at 01:25:46PM +0100, Usama Arif wrote: >>> When memory allocation profiling is running on memory bound services, >>> allocations greater than order 0 for slab object extensions can fail, >>> for e.g. zs_handle zswap slab which will be 512 objsperslab x 16 bytes >>> per slabobj_ext (order 1 allocation). Use kvcalloc to improve chances >>> of the allocation being successful. >>> >>> Signed-off-by: Usama Arif >>> Reported-by: Vlad Poenaru >>> Closes: https://lore.kernel.org/all/17fab2d6-5a74-4573-bcc3-b75951508f0a@gmail.com/ >>> --- >>> mm/slub.c | 2 +- >>> 1 file changed, 1 insertion(+), 1 deletion(-) >>> >>> diff --git a/mm/slub.c b/mm/slub.c >>> index dc9e729e1d26..bf43c403ead2 100644 >>> --- a/mm/slub.c >>> +++ b/mm/slub.c >>> @@ -1989,7 +1989,7 @@ int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s, >>> gfp &= ~OBJCGS_CLEAR_MASK; >>> /* Prevent recursive extension vector allocation */ >>> gfp |= __GFP_NO_OBJ_EXT; >>> - vec = kcalloc_node(objects, sizeof(struct slabobj_ext), gfp, >>> + vec = kvcalloc_node(objects, sizeof(struct slabobj_ext), gfp, >>> slab_nid(slab)); >> >> And what's the latency going to be on a vmalloc() allocation when we're >> low on memory? > > Would it not be better to get the allocation slighly slower than to not get > it at all? Also a majority of them are less than 1 page. kvmalloc of less than 1 page falls back to kmalloc. So vmalloc will only be on those greater than 1 page size, which are in the minority (for e.g. zs_handle, request_sock_subflow_v6, request_sock_subflow_v4...).