The template fast path currently uses memcpy() for the actual struct page copy. Switch zone_device_page_init_from_template() to memcpy_nt() and add memcpy_nt_drain() before memmap_init_compound(), before prep_compound_head() updates overlapping tail metadata, and before returning from memmap_init_zone_device().
ZONE_DEVICE memmap initialization is largely write-once: each struct page is populated once, and most destination cachelines are not expected to be reused immediately afterwards. On x86, a regular cached memcpy() can therefore incur write-allocate traffic by pulling destination cachelines into the cache before writeback, and can populate the cache with data that has little near-term reuse. Using memcpy_nt() lets this path request non-temporal stores for that copy pattern, which can reduce cache pollution and avoid part of the associated write-allocate overhead, while architectures without a specialized backend still fall back to memcpy(). When memcpy_nt() maps to non-temporal stores, order those stores before memmap_init_compound(), before prep_compound_head() updates overlapping compound metadata, and before returning from memmap_init_zone_device(). Keep sanitized builds on the slow path so KASAN/KMSAN retain their instrumented stores. Tested in a VM with a 100 GB fsdax namespace device configured with map=dev and a 100 GB devdax namespace (align=2097152) on Intel Ice Lake server. Test procedure: Rebind the nd_pmem and dax_pmem driver 30 times and collect the memmap initialization time from the pr_debug() output of memmap_init_zone_device(). Base(v7.2-rc1): First binding for nd_pmem driver: 1456 ms Average of subsequent rebinds: 244.28 ms First binding for dax_pmem driver: 1462 ms Average of subsequent rebinds: 273.31 ms With this series: First binding for nd_pmem driver: 1272 ms Average of subsequent rebinds: 96.79 ms First binding for dax_pmem driver: 1354 ms Average of subsequent rebinds: 119.04 ms This reduces the average rebind time by about 60.4% for nd_pmem and 56.4% for dax_pmem. Signed-off-by: Li Zhe <[email protected]> --- mm/mm_init.c | 39 +++++++++++++++++++++++++++++++++++++-- 1 file changed, 37 insertions(+), 2 deletions(-) diff --git a/mm/mm_init.c b/mm/mm_init.c index fb855bb0437a..addb4969587e 100644 --- a/mm/mm_init.c +++ b/mm/mm_init.c @@ -1067,11 +1067,21 @@ static void __ref zone_device_page_init_slow(struct page *page, static inline bool zone_device_page_init_optimization_enabled(void) { + /* + * Keep sanitized builds on the slow path so their stores stay + * instrumented. + */ + if (IS_ENABLED(CONFIG_KASAN) || IS_ENABLED(CONFIG_KMSAN)) + return false; + /* * The template fast path copies a preinitialized struct page image. * Skip it when the page_ref_set tracepoint is enabled. */ - return !page_ref_tracepoint_active(page_ref_set); + if (page_ref_tracepoint_active(page_ref_set)) + return false; + + return true; } static inline void zone_device_tail_page_init(struct page *page, @@ -1110,7 +1120,7 @@ static void zone_device_page_init_from_template(struct page *page, * to the destination page. */ zone_device_page_update_template(template, pfn); - memcpy(page, template, sizeof(*page)); + memcpy_nt(page, template, sizeof(*page)); } /* @@ -1179,6 +1189,15 @@ static void __ref memmap_init_compound(struct page *head, &template); } } + + /* + * When the template path is enabled, order the preceding tail-page copies + * before prep_compound_head() updates the overlapping compound metadata + * in the first tail-page descriptors. If memcpy_nt() fell back to + * regular cached stores, memcpy_nt_drain() may be a no-op. + */ + if (use_template) + memcpy_nt_drain(); prep_compound_head(head, order); } @@ -1238,10 +1257,26 @@ void __ref memmap_init_zone_device(struct zone *zone, if (pfns_per_compound == 1) continue; + /* + * When the template path is enabled, order the preceding head-page copy + * before memmap_init_compound(), which immediately updates compound-head + * metadata. If memcpy_nt() fell back to regular cached stores, + * memcpy_nt_drain() may be a no-op. + */ + if (use_template) + memcpy_nt_drain(); + memmap_init_compound(page, pfn, zone_idx, nid, pgmap, compound_nr_pages(pfn, altmap, pgmap), use_template); } + /* + * Ensure any prior template copies are ordered before returning. + * On architectures where memcpy_nt() used regular cached stores, + * memcpy_nt_drain() may be a no-op. + */ + if (use_template) + memcpy_nt_drain(); pageblock_migratetype_init_range(start_pfn, nr_pages, MIGRATE_MOVABLE); -- 2.20.1
