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[2003:d8:2f0a:2e00:89cb:c7f0:82f2:e43c]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3b5e8e0d785sm5385180f8f.59.2025.07.11.12.26.23 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 11 Jul 2025 12:26:24 -0700 (PDT) Message-ID: <9865895d-c9bf-42e2-b813-bdbd39ad3af1@redhat.com> Date: Fri, 11 Jul 2025 21:26:22 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 12/14] mm: add config option for clearing page-extents To: Ankur Arora Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org, 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> <20250710005926.1159009-13-ankur.a.arora@oracle.com> <87qzymocok.fsf@oracle.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: bbfo76kxqazfhr8o5cwqw8gidiowdrs3 X-Rspam-User: X-Rspamd-Queue-Id: 5961440011 X-Rspamd-Server: rspam04 X-HE-Tag: 1752261988-151064 X-HE-Meta: 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 HnLfJA4F fZA7iugCF1HEoyhavQbaIIx02lE6MDVAxh7QlRyStHAAalYOZUBPKIJxXFHDQta3E6eiuQZYa+fhMyc/FAmwYz2L4hOXiQ3MrJNJYAaZYqsd4Ou+rTmeTq3Z6wY9j1vco5LPkh4e0SKfoBJN49IW73hmKfdu27/5Q7CHcqlIW4/axy+xwLXP5Eb9+Q8dp4mGpJSiM5ZKuwORHVedGTNlbfzILH+oE12oBZqmClIn7HnxGJOHlUcTuakSOTsgoDnoYh8+aHTXH8+eu/Ia+7mqAXHRgL1B4GbbZR9EQwTI1hg14f3dPDHvoeQSMNqLpcpO4XhFoz8uLc/NFOM0d2fbDMY7NmgiWsafKndQiTpLfAvXieT03gJUqTPqz2dMgs1z09ns2o4jo4z4kjUZz4e5bCwADrQkzAZrszRDm9I91cc80/qTyEtgguj4CvJRP/VHEudujulF52eyzDYSqGPrsYCAgAOXA5HDcOjH9 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 11.07.25 19:32, Ankur Arora wrote: > > David Hildenbrand writes: > >> On 10.07.25 02:59, Ankur Arora wrote: >>> Add CONFIG_CLEAR_PAGE_EXTENT to allow clearing of page-extents >>> where architecturally supported. >>> This is only available with !CONFIG_HIGHMEM because the intent is to >>> use architecture support to clear contiguous extents in a single >>> operation (ex. via FEAT_MOPS on arm64, string instructions on x86) >>> which excludes any possibility of interspersing kmap()/kunmap(). >>> Signed-off-by: Ankur Arora >>> --- >> >> Staring at the next patch, I think this can easily be squashed into the next >> patch where you add actual MM core support. > > I wanted to do this in a separate patch to explicitly document what the > responsibility of the interface provided by the architecture is. > That said, the commit message didn't actually do a good job of doing > that :D. > > Copying the more detailed commit message from my reply to Andrew, > one important part of the clear_pages() is that it be interruptible > because clear_pages_resched() implicitly depends on it. > >> This is only enabled with !CONFIG_HIGHMEM because the intent is >> to use architecture support to clear contiguous extents in a >> single interruptible operation (ex. via FEAT_MOPS on arm64, >> string instructions on x86). > >> Given that we might be zeroing the whole extent with a single >> instruction, this excludes any possibility of constructing >> intermediate HIGHMEM maps. > > Do you think it is best documented in the next patch in a comment > instead? I would just add + document it as part of the next patch. Looking at the bigger picture now, you introduce ARCH_HAS_CLEAR_PAGES To say whether an architecture provides clear_pages(). Now we want to conditionally use that to optimize folio_zero_user(). Remind me, why do we want to glue this to THP / HUGETLBFS only? I would assume that the code footprint is rather small, and the systems out there that are compiled with ARCH_HAS_CLEAR_PAGES but without THP / HUGETLBFS are rather ... rare (mostly 32BIT x86 only). -- Cheers, David / dhildenb