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[2003:d8:2f4f:700:c9db:579f:8b2b:717c]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-464f5a281f1sm232993015e9.17.2025.09.23.01.14.18 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 23 Sep 2025 01:14:19 -0700 (PDT) Message-ID: Date: Tue, 23 Sep 2025 10:14:18 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v7 13/16] mm: memory: support clearing page ranges To: Andrew Morton , Ankur Arora Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.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: <20250917152418.4077386-1-ankur.a.arora@oracle.com> <20250917152418.4077386-14-ankur.a.arora@oracle.com> <20250917144418.25cb9117d64b32cb0c7908d9@linux-foundation.org> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: B79378000E X-Rspamd-Server: rspam05 X-Stat-Signature: sf7fnn65adpmtyire5t3sp8yapzfxoij X-Rspam-User: X-HE-Tag: 1758615265-246755 X-HE-Meta: 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 g22iB352 kiftUAa5JpPd++fVpboSltD0Ra60v4v3tPMnI+vJTmJf3ezUdrj/Q1R4FxjEP5ISBXnv6yDh/cWnUhnhf0KtT4fDJVU7g/JIg0Ad3Jagc7anloGc9RcjzDxWExIaY/ykJOy86JcUzQF+gkX+TQ+XCr6qmltt2qmseyiV0rbOb+4IjqjRj7YEw7XrHKadikOq9pARw7BcnaagyxJ1Xx94ghkFaFw7O3z7NmUjkk461Z5Peuv67lxgo86txlJoJsBAr4J8h8ZYQQu+A0J0T8br43RFl1wSOIs4sLyJiWuJqu5tom42cUklspMt8nnYUX/mITJQrzh68Rqt4qqT46wqf56YVDJmtO1PSmPSyV6WXHbcndfzFVGivYBC2Coac/bJ/1tuAZq8sHGqLoOyhHSbzMRCKBgYVETfRJhoCatTSH+nXtwXJG8DudcTZgL2ENg1siY+JpyDLPWfi0TM= 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 17.09.25 23:44, Andrew Morton wrote: > On Wed, 17 Sep 2025 08:24:15 -0700 Ankur Arora wrote: > >> Change folio_zero_user() to clear contiguous page ranges instead of >> clearing using the current page-at-a-time approach. Exposing the largest >> feasible length can be useful in enabling processors to optimize based >> on extent. > > This patch is something which MM developers might care to take a closer > look at. I took a look at various revisions of this series, I'm only lagging behind on reviewing the latest series :) > >> However, clearing in large chunks can have two 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; with the local neighbourhood cleared last. > > Has this optimization been shown to be beneficial? > > If so, are you able to share some measurements? > > If not, maybe it should be removed? > >> ... >> >> --- a/mm/memory.c >> +++ b/mm/memory.c >> @@ -7021,40 +7021,80 @@ static inline int process_huge_page( >> return 0; >> } >> >> -static void clear_gigantic_page(struct folio *folio, unsigned long addr_hint, >> - unsigned int nr_pages) >> +/* >> + * Clear contiguous pages chunking them up when running under >> + * non-preemptible models. >> + */ >> +static void clear_contig_highpages(struct page *page, unsigned long addr, >> + unsigned int npages) > > Called "_highpages" because it wraps clear_user_highpages(). It really > should be called clear_contig_user_highpages() ;) (Not serious) You have a point there, though :) Fortunately this is only an internal helper. -- Cheers David / dhildenb