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, copy it into each destination page, and then fix up the PFN-dependent fields after the copy.
The optimized path assigns _refcount through the copied template, so keep it disabled when the page_ref_set tracepoint is enabled. Also fall back to the slow path if struct page is not an integral number of u64 words. 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 patches 1-3 applied: First binding: 1422 ms Average of subsequent rebinds: 245.73 ms This reduces the average rebind time from 273.52 ms to 245.73 ms, or about 10%. Signed-off-by: Li Zhe <[email protected]> --- mm/mm_init.c | 70 +++++++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 69 insertions(+), 1 deletion(-) diff --git a/mm/mm_init.c b/mm/mm_init.c index 4ba506df93bc..2992711351a0 100644 --- a/mm/mm_init.c +++ b/mm/mm_init.c @@ -1066,6 +1066,63 @@ static void __ref zone_device_page_init_slow(struct page *page, zone_device_page_init_pageblock(page, pfn); } +/* + * ZONE_DEVICE depends on MEMORY_HOTPLUG, and MEMORY_HOTPLUG is 64-bit + * only. That means CONFIG_ZONE_DEVICE cannot be enabled on 32-bit + * builds, so this fast-path code does not need a separate 32-bit + * fallback implementation. + */ +static inline bool zone_device_page_init_optimization_enabled(void) +{ + /* + * The template fast path copies a preinitialized struct page as an + * array of u64 words. Skip it when the page_ref_set tracepoint is + * enabled, and fall back to the slow path if struct page is not an + * integral number of u64 words. + */ + return !page_ref_tracepoint_active(page_ref_set) && + IS_ALIGNED(sizeof(struct page), sizeof(u64)); +} + +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 (!zone_device_page_init_refcount(pgmap)) + set_page_count(template, 0); +} + +/* + * The copied template already provides the PFN-invariant portion of a + * ZONE_DEVICE struct page. Fix up the fields that still depend on @pfn + * after the copy, namely the section bits and page->virtual when present. + */ +static inline void zone_device_page_init_finish(struct page *page, + unsigned long pfn) +{ + set_page_section_from_pfn(page, pfn); +#ifdef WANT_PAGE_VIRTUAL + if (!is_highmem_idx(ZONE_DEVICE)) + set_page_address(page, __va(pfn << PAGE_SHIFT)); +#endif +} + +static void zone_device_page_init_from_template(struct page *page, + unsigned long pfn, const struct page *template) +{ + const u64 *src = (const u64 *)template; + u64 *dst = (u64 *)page; + unsigned int i; + + for (i = 0; i < sizeof(struct page) / sizeof(u64); i++) + dst[i] = src[i]; + zone_device_page_init_finish(page, pfn); + 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 @@ -1114,6 +1171,7 @@ 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); @@ -1121,6 +1179,7 @@ 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; @@ -1135,10 +1194,19 @@ 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
