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TKfHkcgOQ2SMJhjamjwR1M5k+zmYUYdu6MEItZZEMBC4avqIXMZOjJVc8IZtQMAqekIQHNBW9S/ 43h90zzhbJRFNYI5SGst0OahUNhFg7yZg+eYeYIsjV2NZPbEEg/C7MmUxOFHomWwx1ys96zWWMz bKWiymDsZoygjFl23kC5MEUTnaszjgtIJDsvSjnI2EgJEeE604x61BOv+PQWiJemyDJa+z3CAno Ya8BXtEAEvlXmHDA2qg7ZdEaQIW65eMERVN8RoBlHpsPm/o3+TE= X-Proofpoint-ORIG-GUID: 7NnEx7-uLqRWKP_F9aJJNQTK-KxnBjD3 X-Proofpoint-GUID: 7NnEx7-uLqRWKP_F9aJJNQTK-KxnBjD3 X-Authority-Analysis: v=2.4 cv=PMcCOPqC c=1 sm=1 tr=0 ts=68e4b085 b=1 cx=c_pps a=e1sVV491RgrpLwSTMOnk8w==:117 a=e1sVV491RgrpLwSTMOnk8w==:17 a=6eWqkTHjU83fiwn7nKZWdM+Sl24=:19 a=z/mQ4Ysz8XfWz/Q5cLBRGdckG28=:19 a=lCpzRmAYbLLaTzLvsPZ7Mbvzbb8=:19 a=xqWC_Br6kY4A:10 a=x6icFKpwvdMA:10 a=GoEa3M9JfhUA:10 a=zd2uoN0lAAAA:8 a=yPCof4ZbAAAA:8 a=_OrDgAD2IhgNzo2bdpcA:9 cc=ntf awl=host:13625 Raghavendra K T writes: > 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 Thanks Raghu. -- ankur