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 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 9/18/2025 3:14 AM, 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. > >> 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? > I reverted the effect of this patch by hard coding #define PAGE_CONTIG_NR 1 I see that benefit for voluntary kernel is lost without this change (for rep stosb) with PAGE_CONTIG_NR equivalent to 8MB Preempt mode: voluntary # Running 'mem/mmap' benchmark: # function 'demand' (Demand loaded mmap()) # Copying 64GB bytes ... 34.533414 GB/sec with PAGE_CONTIG_NR equivalent to 4KB # Running 'mem/mmap' benchmark: # function 'demand' (Demand loaded mmap()) # Copying 64GB bytes ... 20.766059 GB/sec For now (barring David's recommendations), feel free to add Reviewed-by: Raghavendra K T