From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from va-1-112.ptr.blmpb.com (va-1-112.ptr.blmpb.com [209.127.230.112]) (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 9C8223B2FDB for ; Wed, 1 Jul 2026 09:08:56 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.127.230.112 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782896940; cv=none; b=W9LUX2SSIiXjrZzuxg8cTWg8T5RZhzwtrzSJUEqaUWWG+EpHbNVAKg+Bo17XYHSgzaRzNRJykjaF1LB8dyudv9M3xTnTmoC8dPNkKCvFA5I1gvQP4lQrP3dpx6iifZCWuwfV/qxKmRWXxyPF8VjzzouzhCVaSnvHoyhM20hUc08= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782896940; c=relaxed/simple; bh=svQWzxEVmxgAbEyJ6zcLPMSDVD32mcJAkW2hgkQlf0E=; h=Mime-Version:References:Content-Type:Cc:Subject:To:From: In-Reply-To:Date:Message-Id; b=daIGypdRMNnbPFWpedUBPs2x6yQUv0RtkV+itsid3hqlh8ZPQWI1XerQCR18z4q3xA33+KiZ5/taIx88whHqwBAed4qc+JXNO5fIqKdK8IyqleB/x0fVpcCbPGArZUcQXE/F5BT8v23b61Se9ezpJNtnZMI8MylVe+EPrJbUJFw= 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=Z2axJOc0; arc=none smtp.client-ip=209.127.230.112 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="Z2axJOc0" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; s=2212171451; d=bytedance.com; t=1782896931; h=from:subject: mime-version:from:date:message-id:subject:to:cc:reply-to:content-type: mime-version:in-reply-to:message-id; bh=/4LpGd1s160eDq45kTLayWuXfCywKUfCzxMxs45e1/A=; b=Z2axJOc0VO7AxiEyvJIs1079BbQWS5QAKOqh4D16BOKQED38V2mn+wp3ryfn/04sCnqtO3 n4hyoSzvFfATOSNW6c5ISjiJAAHsUoTPgtjI5M7ZFznL1V6odxPRi/Lc+Jv4t4yJpi6F0R tcBFQDTn2AW2ByiWyeJgEHJ+Y10CaW29Lpi60NNF4OpVHORPrJbDEeh4DvwKWKoKeF7KEi noIcFSxXZZqCHDfzW/Ru2/zB0y5MXsYeiomAgeK3wD4K4+IjD8186elRGdJirZ+/3+gHmz Ff3fV4tijmXfIBbJauislEcwRHvnyWhut0cwqptt5s6eIDsV6FcF+jBrc38uPA== Precedence: bulk X-Mailing-List: linux-arch@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260701090553.62691-1-lizhe.67@bytedance.com> Content-Type: text/plain; charset=UTF-8 Cc: , , , , , Subject: [PATCH v5 5/8] mm: extend the template fast path to zone-device compound tails Content-Transfer-Encoding: 7bit X-Lms-Return-Path: To: , , , , , , , , , From: "Li Zhe" X-Original-From: Li Zhe X-Mailer: git-send-email 2.45.2 In-Reply-To: <20260701090553.62691-1-lizhe.67@bytedance.com> Date: Wed, 1 Jul 2026 17:05:50 +0800 Message-Id: <20260701090553.62691-6-lizhe.67@bytedance.com> 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(v7.2-rc1): First binding: 1462 ms Average of subsequent rebinds: 273.31 ms With this patch and its prerequisites applied: First binding: 1403 ms Average of subsequent rebinds: 244.37 ms This reduces the average rebind time from 273.31 ms to 244.37 ms, or about 10.6%. Signed-off-by: Li Zhe --- mm/mm_init.c | 47 ++++++++++++++++++++++++++++++++++++++++------- 1 file changed, 40 insertions(+), 7 deletions(-) diff --git a/mm/mm_init.c b/mm/mm_init.c index cc8417951467..60794050bc07 100644 --- a/mm/mm_init.c +++ b/mm/mm_init.c @@ -1081,6 +1081,16 @@ 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 @@ -1138,10 +1148,12 @@ 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. @@ -1150,12 +1162,31 @@ 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); } @@ -1205,7 +1236,8 @@ 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(start_pfn, altmap, pgmap)); + compound_nr_pages(start_pfn, altmap, pgmap), + use_template); pfn += pfns_per_compound; } @@ -1226,7 +1258,8 @@ void __ref memmap_init_zone_device(struct zone *zone, continue; memmap_init_compound(page, pfn, zone_idx, nid, pgmap, - compound_nr_pages(pfn, altmap, pgmap)); + compound_nr_pages(pfn, altmap, pgmap), + use_template); } pageblock_migratetype_init_range(start_pfn, nr_pages, MIGRATE_MOVABLE); -- 2.20.1