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Tue, 14 Oct 2025 16:02:29 +0800 (CST) Received: from dggpemf100008.china.huawei.com (unknown [7.185.36.138]) by mail.maildlp.com (Postfix) with ESMTPS id C7ED3140144; Tue, 14 Oct 2025 16:02:48 +0800 (CST) Received: from [10.174.177.243] (10.174.177.243) by dggpemf100008.china.huawei.com (7.185.36.138) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.11; Tue, 14 Oct 2025 16:02:47 +0800 Message-ID: <364ceb89-6327-498a-9582-bb1fbe2bd98e@huawei.com> Date: Tue, 14 Oct 2025 16:02:44 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/3] mm: mprotect: avoid unnecessary struct page accessing if pte_protnone() To: David Hildenbrand , Andrew Morton , Lorenzo Stoakes , CC: Zi Yan , Baolin Wang , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , References: <20251013121536.2373249-1-wangkefeng.wang@huawei.com> <20251013121536.2373249-3-wangkefeng.wang@huawei.com> <93d00bb0-8aa7-4f52-b9ba-ef777ec191dc@redhat.com> <4469b9c3-3656-44f5-897d-b024e030587f@huawei.com> <93736a75-3fc5-47b0-8985-96e1b0b98b8a@redhat.com> Content-Language: en-US From: Kefeng Wang In-Reply-To: <93736a75-3fc5-47b0-8985-96e1b0b98b8a@redhat.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.177.243] X-ClientProxiedBy: kwepems200001.china.huawei.com (7.221.188.67) To dggpemf100008.china.huawei.com (7.185.36.138) X-Rspamd-Server: rspam05 X-Stat-Signature: 8t78dbfq17tzyuci9nam165qbhwpdc1a X-Rspam-User: X-Rspamd-Queue-Id: 216C740012 X-HE-Tag: 1760428973-795494 X-HE-Meta: U2FsdGVkX19r4rvmZ3UICus77dNAlks6ydCKQXCQ4ETKTzkMnthtJW0otrxa73Mdb2twvACZfumXoVpJiLFcMTZo8lV8BCDH3qm5MhEu0DGeCbrgx6jUb3bI0FlwEl4dbcnpSyaBY4lDtQsG9525jCu3hMtGxeClxeF1nJ6EsY7/QdamE83b/kNEbdyN6cLbBanzJLJDZX1qwEhMtpDGCWeASjk03ndpXfc5kSYwuKhxF7mB9mmGZje/m5TOZn/WGy1D5Cxge9tF4G4Bc7fhvuotDv32a3KnlvNTElltAtuwkg6/fA04XzHxEvzAYTGzfVGWKazXM3oKM3cyAEA5Als3YhvKaO67XhVfL4+6Zh94ezrzRb4AH2Dezgj3U0GHyF3tnpwTA0kkWQj3kJnestMzCvaKYQ9NpAGkuHbrQON5KG99c3HZr5SX0rf6qNZmHVsicKO1jiVAEWJYAs03rQ6OsumEVXr/LWJe4DR9wTe6WAx2ou/Acx5nvZJdcdJjOgzUdiZNuVrlCKSdb2/I0bJ5dNCKzEZT3ioXj0rMSV1dj19zX2ghmgbi0lVrM3c3hSQC1xDr6A8lRJ/cbNxrwahjX131VNoOIW/qLyVxXuw7h8MnrRJBdjGO/KFqRBzy5clfvWipjFTeqiCo+6v086xtoxJB52uTej83qg3BvPTMdm5Ou5YQiC+mkmJ7eS90bDPeEzlhT1F9H7unyrXXREVSKrexPv7Y9HJGRdyWx4UNQI3lZ/O/3GZ/tOflVSfb6rvoi5MO5NSk7kEu5kZWC0SR0Z7E2B2e/zIRFZT6Mar+w6QDPd6HTP5VdH8wkEE0FpvM0oXFZbjJ+LvSUkcMxcPTBvklfOtHzIRm5AAfKQdtFw+eD6gTgpw1hc0jg9JfzvUyALgEJzOQf9dddIkfNaw86yzP+mZ0PJ7Jizn2Em3npFbYvHPPJ5skuVnECbHJ4is8inNbXX5DiWfwYPb 0ckxh3ih y7mtlobnMvHNpGqzujzms7cXTWQXrFS+XHwI8J/BT6MOOKcdvlA3lnzfGU7nTAuq5pD4JkojBFNspSL2e1ir4JclUfhx3UuCHJflDqTxblz8ZwzKo1WQC5RKoUjYl7OdwOBM5n6o82ahXwcPe+gNmUOMPoM73I0ayxAjY5MYMXR0R/BvB2mtJpx+YoV8pkgIkJJmi1nYHrRgM46Q9hYrQAr6qRTPlcq4rojkeY47JsY8nszI1uQQ7Hpd1uD+5VULWYKldglKg8fhXrccS+xSpNbIFjUl04RhCCSwaI053RxcT7twKlC+3O90vO3rFumtdMeXevSccuQqRlVxPObqeg3PbfFpfCZTedLBYm35uAcWyj7KKY/n1CXP2sQG0Tzd/sRn2g8T2tzRdLyEX6dar4omnH9Aew6JKHbFFKsz7Rq4QbQEEtTK8RbOjMg== 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: List-Subscribe: List-Unsubscribe: On 2025/10/14 15:16, David Hildenbrand wrote: >>> >>>> +            if (prot_numa && pte_protnone(oldpte)) >>>> +                continue; >>>> + >>>>                page = vm_normal_page(vma, addr, oldpte); >>>>                if (page) >>>>                    folio = page_folio(page); >>> >>> I could have sworn we discussed that while fixing the prot_numa_skip() >>> fallout. >> >> I'm not follow the thread, but we found that vm_normal_page does >> introduce regression for mprotect benchmark(libMicro) with >> this vm_normal_page(). >> > > Right, I raised it here: > > https://lkml.kernel.org/r/aa496798-5ac6-4cb0-bdc2-91515172e935@redhat.com Thanks for the links, let's fix it now ;) > > I questioned how relevant it would be in practice. > > I'm surprised it shows up in a mprotect() benchmark: mprotect() itself > would never be able to set MM_CP_PROT_NUMA, so the code wold not > actually be executed. > Sorry, my description is very clear, the regression is not about prot numa, I mean the vm_normal_page does introduce some regression when mprotect benchmark in libMicro, before cac1db8c3aad （"mm: optimize mprotect() by PTE batching"), we only call vm_normal_page in can_change_pte_writable(), but now it is unconditional called and 10% regression in some libMicro mprotect benchmark. We could add limit to call of vm_normal_page， eg，cp_flags check, and using pte_batch_hint, but it is unclear whether it is worth doing so.