From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from va-1-115.ptr.blmpb.com (va-1-115.ptr.blmpb.com [209.127.230.115]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D8ADB407CCE for ; Wed, 3 Jun 2026 08:05:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.127.230.115 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780473938; cv=none; b=ZTmPbG7AjdSJTE41gRQ2bCkeb0tM/FWGu1Y0yXCZNGnqvT9EZ1oInwLNV6MofEPTmR9DWuWpdTFOxzTe9W82w4SmKIOaIafdvQk7YIlch0KgfSy26+EatXhfVNCbqM5hlOC/9a/2e19p9ewM5K4JnCa8rI0z6Idoe15EfNcUmMI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780473938; c=relaxed/simple; bh=/pYgzuRQ6iq6nYtxlWbo/GZKyUbyCI63h8deMoKd5M0=; h=To:Subject:Message-Id:In-Reply-To:References:Date:From: Content-Type:Cc:Mime-Version; b=UfgRTi0D9EEPzI0T3AxQwdkG7xa3ZdfqqVpRownAYpo6hQI1H8zd57HC7A3Q9uxpARNo2kztkxN+Q2+zpJalFCsXjk86c7P6II6pVLgKdn/E0+sqlBTCbPv5Kfa5MLFTnKYICufnEhPAU/3Ucp7vvqsNxBwJ02xP2lEAQbAVHrc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=bytedance.com; spf=pass smtp.mailfrom=bytedance.com; dkim=pass (2048-bit key) header.d=bytedance.com header.i=@bytedance.com header.b=ZLrF88yr; arc=none smtp.client-ip=209.127.230.115 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=bytedance.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=bytedance.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=bytedance.com header.i=@bytedance.com header.b="ZLrF88yr" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; s=2212171451; d=bytedance.com; t=1780473932; h=from:subject: mime-version:from:date:message-id:subject:to:cc:reply-to:content-type: mime-version:in-reply-to:message-id; bh=yy6XV8hK8oauYu/xVX9D1lPDIbV+Br2ZbBHBJaftx+0=; b=ZLrF88yrw0Nzm2arTnuzExC5kIY/vk+nde66tD5n4K7wAdlp8Y4KcqGSZTG+Ron/yDXItV GoEPagz8RFHgpXEFcKw8l44nkDsEnRI0f0h3Qy7Ke5b+k+3awfWUhUV7zyvZ2c6fK24d4E CznItthwfvCx5Di0TfFWL2mt4vyATW7tjB0kN8DokSactI8q1U7dKDmBMqMgvBrRVdVTpL PxIL4JmeIUKa9WLnwZF1gVlV6NvJjWdBHs8jL2oxj+fcwEB1Y5zXI5P0QOgHGpIXgonH71 OvQWensr1Q/3a0Et0oPJFBj0FjKGp5noK19664J4PsS4BSO49ekAaIDU7LkH/w== Content-Transfer-Encoding: 7bit To: , , , , , , , , , Subject: [PATCH v4 4/8] mm: add a template-based fast path for zone-device page init Message-Id: <20260603080152.64728-5-lizhe.67@bytedance.com> In-Reply-To: <20260603080152.64728-1-lizhe.67@bytedance.com> References: <20260603080152.64728-1-lizhe.67@bytedance.com> X-Original-From: Li Zhe Date: Wed, 3 Jun 2026 16:01:48 +0800 From: "Li Zhe" X-Lms-Return-Path: X-Mailer: git-send-email 2.45.2 Content-Type: text/plain; charset=UTF-8 Cc: , , , , , Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 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(v7.1-rc6): First binding: 1466 ms Average of subsequent rebinds: 262.12 ms With this patch and its prerequisites applied: First binding: 1432 ms Average of subsequent rebinds: 246.30 ms This reduces the average rebind time from 262.12 ms to 246.30 ms, or about 6%. Signed-off-by: Li Zhe --- mm/mm_init.c | 76 ++++++++++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 74 insertions(+), 2 deletions(-) diff --git a/mm/mm_init.c b/mm/mm_init.c index 2e5899c5cf35..56fe71e966ae 100644 --- a/mm/mm_init.c +++ b/mm/mm_init.c @@ -1068,6 +1068,51 @@ 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, + 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)); + 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 +1161,7 @@ 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 +1169,7 @@ 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 +1184,35 @@ void __ref memmap_init_zone_device(struct zone *zone, 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(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 (pfns_per_compound == 1) continue; -- 2.20.1