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 6CCD13ECBE4 for ; Mon, 27 Jul 2026 12:36:37 +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=1785155799; cv=none; b=urSp4ZlRVJNFNgDcxbaFQ4EfiXzVHz4HyupR8TEFvDTg0PyUzza2gnquGwQAjS8Pg2Ztm8V65/lB+AXYlXJSXKXrHbUlffeF+Y7LaEehSnotL054UEiXVM6AAGMlqNYLIs55+PvZvRK8A7s4XRNyJJCBfRisPz5MjNw7Oe6lBms= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785155799; c=relaxed/simple; bh=qgr93Zs18EPBcOvB82j2q2F+PNjlHHhMDXF5BEM6q6Q=; h=References:Content-Type:Subject:To:Cc:Date:Message-Id:From: Mime-Version:In-Reply-To; b=U8PwTVF1WfxnWOs9trUBKCIiBGG9GkowwuW1Spq3+165DY4hBt11VTSHMK804SdNUKmtrsfQPPMBjlJEnFm1Z2lecDfTUaObS389maLiYcMMOq+RDJ8TedlB5j8tkyUacJFzSMKuGEkfG4cGtphaFFFjcgp7OvIlSFUf3apEink= 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=fDQU/xTj; 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="fDQU/xTj" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; s=2212171451; d=bytedance.com; t=1785155792; h=from:subject: mime-version:from:date:message-id:subject:to:cc:reply-to:content-type: mime-version:in-reply-to:message-id; bh=1OXSJ03+XyIqi02GqEj3ajlM+g5iP3d6qhTy7H8GWxg=; b=fDQU/xTjRXRvHzm00RtjJXifoTKo/HY6KHFE93o6Jsxn1Q9J1dV1wQfrHTnBxStcTJMpWl pvvSXcZwXjHuqpRuMmHoFT9qzMERP4PGct734jfV85ZEgcSjzHqsP5ZIOfplsxs4KKWOld 7ahFK0+IeJawzafxzuytopjGCyKyTQldKFac4Njq4jnYjXexxZNhvPKl94ObVxAixB/z6s N8ITLirPTSB+7LcKDgztDP+50G5gl3sPvNUe4eHN0vEGyvLuGYMO+dCNQ6L/DBuJHXfI4n UugPwt89X9jkq21cFHG+ss+PNuDjHW59xlVLblo14Xwf0v4yuZ117fIOdbBClQ== References: <20260727123429.5673-1-lizhe.67@bytedance.com> Content-Type: text/plain; charset=UTF-8 Subject: [PATCH v8 4/9] mm: add a template-based fast path for zone-device page init To: , , , , , , , , , , , Cc: , , , , , Date: Mon, 27 Jul 2026 20:34:24 +0800 Message-Id: <20260727123429.5673-5-lizhe.67@bytedance.com> X-Lms-Return-Path: X-Mailer: git-send-email 2.45.2 From: "Li Zhe" Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 In-Reply-To: <20260727123429.5673-1-lizhe.67@bytedance.com> Content-Transfer-Encoding: 7bit X-Original-From: Li Zhe 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 memmap initialization time measured during rebind from 244.28 ms to 217.19 ms, or about 11%. Signed-off-by: Li Zhe --- mm/mm_init.c | 59 +++++++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 58 insertions(+), 1 deletion(-) diff --git a/mm/mm_init.c b/mm/mm_init.c index a70acb7431a6..c2645b9bcef3 100644 --- a/mm/mm_init.c +++ b/mm/mm_init.c @@ -1065,6 +1065,44 @@ static void __ref zone_device_page_init_slow(struct page *page, 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); +} + +/* + * '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 @@ -1120,6 +1158,7 @@ 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); @@ -1127,6 +1166,7 @@ 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 +1184,24 @@ 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 (!use_template) { + zone_device_page_init_slow(page, pfn, zone_idx, + nid, pgmap); + } else if (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. + */ + 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