From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 57B7E3264FF for ; Thu, 2 Jul 2026 16:03:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783008233; cv=none; b=OhuQt9yOOiKnyi8IyMTX++xWKwn3Lp2mUm0fBHRS7nUESARb4VUjCvLJe9rDFzlBxpUBkPU6erR+XgyMZJZan72uHri5Su+VK8eP4ZB6Y2eF0CoTnq/U9SHhfE2fWQ6yV2AFVwLqLnzu+pAp56NgjES8KtkitY3i0tfFs8RJ6bQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783008233; c=relaxed/simple; bh=3gmMwU4J4UxlduQ3aCEJN+Vp6EHCnkrDvSTxrZw4gag=; h=Date:To:From:Subject:Message-Id; b=Xkd2OjuS9Wev5C5tWrWN5k6xv4mTdm6AxTp1Bt4do6nF2ns6hbbB3JUn/Df72icj5aMTEiX5tUmxLk6Cvvj0+LwDk/UXyI7m9e+s3TgfatuHWzZ5wmvpv3sNWtzT2Bt0T5fB9gRmTD+JBy920sbc577nj/HBbSOAfdQpomBdHdo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=baY7A4Cm; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="baY7A4Cm" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 202511F00A3E; Thu, 2 Jul 2026 16:03:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1783008232; bh=NTZXb1ao8w+z0fRA+Hw2h0/+cMALI4SHwOZtdACp+wE=; h=Date:To:From:Subject; b=baY7A4CmNFJYU0VsmCXyuCVIpjHgffK/MLpfxMFx5YmG04e6xBv7v2Dj2MaELlh+U jcILqowpDQ96pW1kLe2LVSxEfn0BISj8kXITeHfPj8Xo4qBpcGDNpBMN/q67TKRHco qSofXtXCWP0EyZP17cYb/huzElG83UmT7DsjfYHU= Date: Thu, 02 Jul 2026 09:03:51 -0700 To: mm-commits@vger.kernel.org,lizhe.67@bytedance.com,akpm@linux-foundation.org From: Andrew Morton Subject: [to-be-updated] mm-add-a-template-based-fast-path-for-zone-device-page-init.patch removed from -mm tree Message-Id: <20260702160352.202511F00A3E@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The quilt patch titled Subject: mm: add a template-based fast path for zone-device page init has been removed from the -mm tree. Its filename was mm-add-a-template-based-fast-path-for-zone-device-page-init.patch This patch was dropped because an updated version will be issued ------------------------------------------------------ From: "Li Zhe" Subject: mm: add a template-based fast path for zone-device page init Date: Wed, 1 Jul 2026 17:05:49 +0800 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 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): First binding: 1456 ms Average of subsequent rebinds: 244.28 ms With this patch and its prerequisites applied: First binding: 1440 ms Average of subsequent rebinds: 217.19 ms This reduces the average rebind time from 244.28 ms to 217.19 ms, or about 11%. Link: https://lore.kernel.org/20260701090553.62691-5-lizhe.67@bytedance.com Signed-off-by: Li Zhe Cc: Alistair Popple Cc: Arnd Bergmann Cc: Balbir Singh Cc: "Borislav Petkov (AMD)" Cc: David Hildenbrand Cc: Ingo Molnar Cc: Kees Cook Cc: Mike Rapoport (Microsoft) Signed-off-by: Andrew Morton --- mm/mm_init.c | 76 +++++++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 74 insertions(+), 2 deletions(-) --- a/mm/mm_init.c~mm-add-a-template-based-fast-path-for-zone-device-page-init +++ a/mm/mm_init.c @@ -1056,6 +1056,50 @@ static void __ref zone_device_page_init_ set_page_count(page, 0); } +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, + struct page *src) +{ + memcpy(template, src, sizeof(*template)); +} + +/* + * '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 @@ -1111,6 +1155,7 @@ void __ref memmap_init_zone_device(struc 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); @@ -1118,6 +1163,7 @@ void __ref memmap_init_zone_device(struc 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; @@ -1132,10 +1178,36 @@ void __ref memmap_init_zone_device(struc nr_pages = end_pfn - start_pfn; } - for (pfn = start_pfn; pfn < end_pfn; pfn += pfns_per_compound) { - struct page *page = pfn_to_page(pfn); + + if (!nr_pages) + return; + + pfn = start_pfn; + /* + * Seed the reusable head-page template from the first real struct + * page, because the existing page-init and pageblock helpers expect + * a real memmap entry rather than a stack object. + */ + if (use_template) { + struct page *page = pfn_to_page(start_pfn); zone_device_page_init_slow(page, pfn, zone_idx, nid, pgmap); + zone_device_template_page_init(&template, page); + if (pfns_per_compound != 1) + memmap_init_compound(page, pfn, zone_idx, nid, pgmap, + compound_nr_pages(start_pfn, altmap, pgmap)); + pfn += pfns_per_compound; + } + + for (; pfn < end_pfn; pfn += pfns_per_compound) { + struct page *page = pfn_to_page(pfn); + + 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 (IS_ALIGNED(pfn, PAGES_PER_SECTION)) cond_resched(); _ Patches currently in -mm which might be from lizhe.67@bytedance.com are mm-extend-the-template-fast-path-to-zone-device-compound-tails.patch string-introduce-memcpy_nt-helpers.patch x86-string-extend-memcpy_flushcache-fixed-size-fastpaths.patch mm-use-memcpy_nt-in-zone-device-template-copies.patch