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[2003:d8:2f3c:3a00:5662:26b3:3e5d:438e]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-454d512c2bfsm82539525e9.39.2025.07.11.04.44.15 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 11 Jul 2025 04:44:16 -0700 (PDT) Message-ID: <4fa268f0-d56d-4b6c-aced-06e7002efd28@redhat.com> Date: Fri, 11 Jul 2025 13:44:15 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 13/14] mm: memory: support clearing page-extents To: Ankur Arora , linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org Cc: akpm@linux-foundation.org, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, mingo@redhat.com, mjguzik@gmail.com, luto@kernel.org, peterz@infradead.org, acme@kernel.org, namhyung@kernel.org, tglx@linutronix.de, willy@infradead.org, raghavendra.kt@amd.com, boris.ostrovsky@oracle.com, konrad.wilk@oracle.com References: <20250710005926.1159009-1-ankur.a.arora@oracle.com> <20250710005926.1159009-14-ankur.a.arora@oracle.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 89C41180004 X-Stat-Signature: ozwjbnit4xzmddafxnwrwq1foddwhfsb X-Rspam-User: X-HE-Tag: 1752234262-47678 X-HE-Meta: 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 fA6wQQuU Gq4OcEIzaYaBFOBbGs5UoyyZ14oWn51fzKKOGx/gCvxpw64/axJQEKtnBNfEOO+7QPVedkQLaRv7Ypkk= 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 10.07.25 02:59, Ankur Arora wrote: > folio_zero_user() is constrained to clear in a page-at-a-time > fashion because it supports CONFIG_HIGHMEM which means that kernel > mappings for pages in a folio are not guaranteed to be contiguous. > > We don't have this problem when running under configurations with > CONFIG_CLEAR_PAGE_EXTENT (implies !CONFIG_HIGHMEM), so zero in > longer page-extents. > This is expected to be faster because the processor can now optimize > the clearing based on the knowledge of the extent. > I'm curious: how did we end up "page extent" terminology? :) "CONFIG_CLEAR_CONTIG_PAGES" or sth. like that would be a bit clearer (pun intended), at least to me. We use "CONTIG" pages already in different MM context. "page extent" reminds of "page_ext", which is "page extension" ... > However, clearing in larger chunks can have two other problems: > > - cache locality when clearing small folios (< MAX_ORDER_NR_PAGES) > (larger folios don't have any expectation of cache locality). > > - preemption latency when clearing large folios. > > Handle the first by splitting the clearing in three parts: the > faulting page and its immediate locality, its left and right > regions; the local neighbourhood is cleared last. > > The second problem is relevant only when running under cooperative > preemption models. Limit the worst case preemption latency by clearing > in architecture specified ARCH_CLEAR_PAGE_EXTENT units. > > Signed-off-by: Ankur Arora > --- -- Cheers, David / dhildenb