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Mon, 26 Oct 2026 02:30:05 -0700 (PDT) Received: from lima-ubuntu.hz.ali.com ([47.246.98.219]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3adebaddd45sm5436708a91.2.2026.10.26.02.30.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 26 Oct 2026 02:30:04 -0700 (PDT) From: Qing Wang To: harry@kernel.org Cc: akpm@linux-foundation.org, cl@gentwo.org, hao.li@linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org, rientjes@google.com, roman.gushchin@linux.dev, vbabka@kernel.org, wangqing7171@gmail.com Subject: Re: [PATCH] mm/slab: only require the requested size when refilling Date: Mon, 26 Oct 2026 17:29:57 +0800 Message-Id: <20261026092957.2305785-1-wangqing7171@gmail.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: References: X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit On Fri, 23 Oct 2026 at 22:22, Harry Yoo wrote: > On Fri, Oct 23, 2026 at 05:44:01PM +0800, Qing Wang wrote: > > kmem_cache_prefill_sheaf() and kmem_cache_refill_sheaf() only guarantee > > @size objects, but for standard capacity sheaves > > __prefill_sheaf_pfmemalloc() uses refill_sheaf(), which actually fills > > the sheaf up to s->sheaf_capacity. > > > > The call thus fails with -ENOMEM > whenever the sheaf cannot be filled > > completely, even when @size objects were already obtained. > > This is extremely rare condition to happen, and so... Yes, I went to measure the number of times of kmem_cache_prefill_sheaf() and kmem_cache_refill_sheaf() in qemu. It's also very low. > > > This leads to needless flushing of the partially > > filled sheaf in kmem_cache_prefill_sheaf(), > > It doesn't make much sense to micro-optimize slab in low or out of > memory situations. I agree with you. Because it's so rare. Thanks for your careful review. -- Best regards, Qing