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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-Archived-By: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: D6CFD14000B X-Stat-Signature: izdykiqaywuh47b9hapwjbkpu9podsws X-Rspam-User: X-Spam-Status: No, score=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_GIT autolearn=no autolearn_force=no version=4.0.1 X-HE-Tag: 1793007006-777296 X-HE-Meta: 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 /ary3CPh ED60rQLvex9LJbKFACjKxnFX+2Dx9sFNJFgeDy8wUgxcqBy9dls7L+7JDGtGJ+B2fZRdICJCTXXlMHPAY9aAAsPmVrvTyJn/aSfUGWIZNF4mobopyDaS6a77lPp++wVH39EB2TPARLsnFr80X0KdFnsmfM74Pb/LNJN5NwF39OK+KDcTKClL+rcuUZIJOYZ6SdbhyEOwQkqFJGBqTj0wgo6OVRkuw5ry2u7cPl85bcph7qcpCdmldDxW+ecG5feaMC7tXswmNCwdykTxvaCup6JrdORM4r0fyPoXw9VCjYYZXyZWo4WKJ29ZKXRrnSWiYQ/r18ra/z6rFDyjsiWqTZx3SiFSyHoG4eTmYnJ7guHi33wDN89HvtMIczEoGcFsyv6Xqom+i9RsUzvES8hkWbQjv9w== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 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