memmap_init_zone_device() repeats nearly identical head-page initialization for each PFN. Prepare one reusable ZONE_DEVICE head-page template through the existing slow path, refresh the PFN-dependent fields in that template before each copy, and memcpy it into each destination page.
The optimized path assigns _refcount through the copied template, so keep it disabled when the page_ref_set tracepoint is enabled. This patch accelerates the pfns_per_compound == 1 case. Compound tails are handled in the next patch. Tested in a VM with a 100 GB fsdax namespace device configured with map=dev on Intel Ice Lake server. This test exercises the nd_pmem rebind path (pfns_per_compound == 1). Test procedure: Rebind the nd_pmem driver 30 times and collect the memmap initialization time from the pr_debug() output of memmap_init_zone_device(). Base(v7.1-rc3): First binding: 1486 ms Average of subsequent rebinds: 273.52 ms With this patch and its prerequisites applied: First binding: 1422 ms Average of subsequent rebinds: 246.65 ms This reduces the average rebind time from 273.52 ms to 246.65 ms, or about 10%. Signed-off-by: Li Zhe <[email protected]> --- mm/mm_init.c | 63 +++++++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 62 insertions(+), 1 deletion(-) diff --git a/mm/mm_init.c b/mm/mm_init.c index 2e5899c5cf35..53c0241c66b7 100644 --- a/mm/mm_init.c +++ b/mm/mm_init.c @@ -1068,6 +1068,56 @@ static void __ref zone_device_page_init_slow(struct page *page, zone_device_page_init_pageblock(page, pfn); } +static inline bool zone_device_page_init_optimization_enabled(void) +{ + /* + * 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); +} + +static inline void zone_device_template_page_init(struct page *template, + unsigned long pfn, + unsigned long zone_idx, + int nid, + struct dev_pagemap *pgmap) +{ + __zone_device_page_init(template, pfn, zone_idx, nid, pgmap); + if (!pagemap_resets_refcount(pgmap)) + set_page_count(template, 0); +} + +/* + * 'template' is a reusable page prototype rather than a strictly immutable + * object. Most ZONE_DEVICE fields stay constant across the pages covered by + * the current template, but section bits and page->virtual may still depend + * on the PFN. Refresh those PFN-dependent fields in the template before + * copying it into @page. + */ +static inline void zone_device_page_update_template(struct page *template, + unsigned long pfn) +{ + set_page_section_from_pfn(template, pfn); +#ifdef WANT_PAGE_VIRTUAL + if (!is_highmem_idx(ZONE_DEVICE)) + set_page_address(template, __va(pfn << PAGE_SHIFT)); +#endif +} + +static void zone_device_page_init_from_template(struct page *page, + unsigned long pfn, struct page *template) +{ + /* + * 'template' carries the invariant portion of a ZONE_DEVICE struct + * page. Update the PFN-dependent fields in place before copying it + * to the destination page. + */ + zone_device_page_update_template(template, pfn); + memcpy(page, template, sizeof(*page)); + zone_device_page_init_pageblock(page, pfn); +} + /* * With compound page geometry and when struct pages are stored in ram most * tail pages are reused. Consequently, the amount of unique struct pages to @@ -1116,6 +1166,7 @@ void __ref memmap_init_zone_device(struct zone *zone, unsigned long nr_pages, struct dev_pagemap *pgmap) { + bool use_template = zone_device_page_init_optimization_enabled(); unsigned long pfn, end_pfn = start_pfn + nr_pages; struct pglist_data *pgdat = zone->zone_pgdat; struct vmem_altmap *altmap = pgmap_altmap(pgmap); @@ -1123,6 +1174,7 @@ void __ref memmap_init_zone_device(struct zone *zone, unsigned long zone_idx = zone_idx(zone); unsigned long start = jiffies; int nid = pgdat->node_id; + struct page template; if (WARN_ON_ONCE(!pgmap || zone_idx != ZONE_DEVICE)) return; @@ -1137,10 +1189,19 @@ void __ref memmap_init_zone_device(struct zone *zone, nr_pages = end_pfn - start_pfn; } + if (use_template) + zone_device_template_page_init(&template, start_pfn, zone_idx, + nid, pgmap); + for (pfn = start_pfn; pfn < end_pfn; pfn += pfns_per_compound) { struct page *page = pfn_to_page(pfn); - zone_device_page_init_slow(page, pfn, zone_idx, nid, pgmap); + if (use_template) + zone_device_page_init_from_template(page, pfn, + &template); + else + zone_device_page_init_slow(page, pfn, zone_idx, + nid, pgmap); if (pfns_per_compound == 1) continue; -- 2.20.1
