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.
Use the template path unconditionally, as suggested by Muchun. The page_ref_set tracepoint is primarily a debugging aid, while this code is still initializing struct pages before they are handed out. From the perspective of users of those pages, the initialization-time refcount transitions are not part of the observable page lifetime. This means page_ref_set will no longer observe every initialization-time refcount assignment for copied ZONE_DEVICE head pages. The impact is controlled because the final initialized struct page state is unchanged, and keeping a separate non-template path only for this local tracepoint observability would add complexity to the common path. This patch accelerates head-page initialization. The pfns_per_compound == 1 case gets the full benefit here, 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(v7.2-rc1): Average of rebinds for nd_pmem driver: 244.28 ms With this patch and its prerequisites applied: Average of rebinds for nd_pmem driver: 215.55 ms This reduces the average memmap initialization time measured during rebind from 244.28 ms to 215.55 ms, or about 11%. Suggested-by: Muchun Song <[email protected]> Suggested-by: Mike Rapoport (Microsoft) <[email protected]> Signed-off-by: Li Zhe <[email protected]> --- mm/mm_init.c | 47 ++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 46 insertions(+), 1 deletion(-) diff --git a/mm/mm_init.c b/mm/mm_init.c index a70acb7431a6..56a36a71ba89 100644 --- a/mm/mm_init.c +++ b/mm/mm_init.c @@ -1065,6 +1065,35 @@ static void __ref zone_device_page_init_slow(struct page *page, set_page_count(page, 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)); +} + /* * 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 @@ -1127,6 +1156,7 @@ 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; @@ -1144,7 +1174,22 @@ void __ref memmap_init_zone_device(struct zone *zone, 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 (pfn == start_pfn) { + /* + * Seed the reusable head-page template from the + * first real struct page. This initializes the + * first page through the existing slow path and + * then reuses that final state as the template + * for subsequent pages. + */ + zone_device_page_init_slow(page, pfn, zone_idx, + nid, pgmap); + /* init template page */ + memcpy(&template, page, sizeof(*page)); + } else { + zone_device_page_init_from_template(page, pfn, + &template); + } if (IS_ALIGNED(pfn, PAGES_PER_SECTION)) cond_resched(); -- 2.20.1
