The template fast path from the previous patch only accelerates head pages. Compound tails in memmap_init_compound() still go through the slow path one by one.
Build separate head and tail templates and reuse one prepared tail template across the tail pages in a compound range. Head pages preserve the existing refcount policy, while compound tails always start with a refcount of 0 after prep_compound_tail(). This extends the template-copy fast path to pfns_per_compound > 1 without changing the existing slow path. Tail-page PFN-dependent fields are refreshed in the reusable tail template before each copy. Tested in a VM with a 100 GB devdax namespace (align=2097152) on Intel Ice Lake server. This test exercises the dax_pmem rebind path and measures memmap initialization latency. Test procedure: Unbind and rebind the dax_pmem driver 30 times, collect memmap initialization time from the pr_debug() output of memmap_init_zone_device(). Base(v7.1-rc6): First binding: 1430 ms Average of subsequent rebinds: 229.12 ms With this patch and its prerequisites applied: First binding: 1336 ms Average of subsequent rebinds: 180.00 ms This reduces the average rebind time from 229.12 ms to 180.00 ms, or about 21.4%. Signed-off-by: Li Zhe <[email protected]> --- mm/mm_init.c | 46 +++++++++++++++++++++++++++++++++++++++------- 1 file changed, 39 insertions(+), 7 deletions(-) diff --git a/mm/mm_init.c b/mm/mm_init.c index 56fe71e966ae..ad078ee354fb 100644 --- a/mm/mm_init.c +++ b/mm/mm_init.c @@ -1083,6 +1083,16 @@ static inline void zone_device_template_page_init(struct page *template, memcpy(template, src, sizeof(*template)); } +static inline void zone_device_tail_page_init(struct page *page, + unsigned long pfn, unsigned long zone_idx, int nid, + struct dev_pagemap *pgmap, const struct page *head, + unsigned int order) +{ + zone_device_page_init_slow(page, pfn, zone_idx, nid, pgmap); + prep_compound_tail(page, head, order); + 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 @@ -1134,10 +1144,12 @@ static void __ref memmap_init_compound(struct page *head, unsigned long head_pfn, unsigned long zone_idx, int nid, struct dev_pagemap *pgmap, - unsigned long nr_pages) + unsigned long nr_pages, + bool use_template) { unsigned long pfn, end_pfn = head_pfn + nr_pages; unsigned int order = pgmap->vmemmap_shift; + struct page template; /* * We have to initialize the pages, including setting up page links. @@ -1146,12 +1158,31 @@ static void __ref memmap_init_compound(struct page *head, * the pages in the same go. */ __SetPageHead(head); - for (pfn = head_pfn + 1; pfn < end_pfn; pfn++) { + + pfn = head_pfn + 1; + /* + * All tails of the same compound page share the state established by + * prep_compound_tail(). Reuse one tail template for the whole range and + * refresh only the PFN-dependent fields in that template before each copy. + */ + if (use_template) { struct page *page = pfn_to_page(pfn); - zone_device_page_init_slow(page, pfn, zone_idx, nid, pgmap); - prep_compound_tail(page, head, order); - set_page_count(page, 0); + zone_device_tail_page_init(page, pfn, zone_idx, nid, + pgmap, head, order); + zone_device_template_page_init(&template, page); + pfn++; + } + + for (; pfn < end_pfn; pfn++) { + struct page *page = pfn_to_page(pfn); + + if (use_template) + zone_device_page_init_from_template(page, pfn, + &template); + else + zone_device_tail_page_init(page, pfn, zone_idx, nid, + pgmap, head, order); } prep_compound_head(head, order); } @@ -1200,7 +1231,7 @@ void __ref memmap_init_zone_device(struct zone *zone, zone_device_template_page_init(&template, page); if (pfns_per_compound != 1) memmap_init_compound(page, pfn, zone_idx, nid, pgmap, - compound_nr_pages(altmap, pgmap)); + compound_nr_pages(altmap, pgmap), use_template); pfn += pfns_per_compound; } @@ -1218,7 +1249,8 @@ void __ref memmap_init_zone_device(struct zone *zone, continue; memmap_init_compound(page, pfn, zone_idx, nid, pgmap, - compound_nr_pages(altmap, pgmap)); + compound_nr_pages(altmap, pgmap), + use_template); } pr_debug("%s initialised %lu pages in %ums\n", __func__, -- 2.20.1
