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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 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 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 Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit 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