From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id C1A5AC44501 for ; Mon, 13 Jul 2026 17:04:42 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id C5DD16B0152; Mon, 13 Jul 2026 13:04:41 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id C0E1C6B015D; Mon, 13 Jul 2026 13:04:41 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id AFDFA6B0174; Mon, 13 Jul 2026 13:04:41 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 72E536B0152 for ; Mon, 13 Jul 2026 13:04:41 -0400 (EDT) Received: from smtpin15.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 4DD57140174 for ; Mon, 13 Jul 2026 13:28:24 +0000 (UTC) X-FDA: 84983832528.15.9E0E1F2 Received: from out-173.mta0.migadu.com (out-173.mta0.migadu.com [91.218.175.173]) by imf03.hostedemail.com (Postfix) with ESMTP id 622C02000E for ; Mon, 13 Jul 2026 13:28:22 +0000 (UTC) Authentication-Results: imf03.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=IbpaFlKp; dmarc=pass (policy=none) header.from=linux.dev; spf=pass (imf03.hostedemail.com: domain of muchun.song@linux.dev designates 91.218.175.173 as permitted sender) smtp.mailfrom=muchun.song@linux.dev ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1783949302; b=W/M4l0RQ/f8CswzdmACAcaH9RNlB6nCB1ksHzf53c3yGhWkTmSobNo1OKotGhNJQJieAUx qFjuG80QggQPQ5n62NhyroWZSrT3MLSjfBxqK92+cR6VaL7bRQuQDarugb2fm5Mgt9+n9j yuV8UrOtn5u9FtYbGTFl8vggfFz5oAM= ARC-Authentication-Results: i=1; imf03.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=IbpaFlKp; dmarc=pass (policy=none) header.from=linux.dev; spf=pass (imf03.hostedemail.com: domain of muchun.song@linux.dev designates 91.218.175.173 as permitted sender) smtp.mailfrom=muchun.song@linux.dev ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1783949302; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=hCZwaMJokj8MvB23i+KgfL9s2fF07ZtloHz25nGxCcw=; b=iw9X+K3lTUq4KyeHB943rOttI1udkZ7x9KylkMkmdqLmcSQnSK+KIisu7U0/zEjEJuR43B GqSipiodYag9khPWaVLRTH2SwAgXyzbqn/nOZpwGvdBTy+PTzT6xMSWAkRscSZtxMfbSKy u3P+gZNLKKtRe/+39F0bUETtOzeO9zI= Message-ID: <03158ab2-94e0-4a48-94d1-df2eedbc5545@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1783949300; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=hCZwaMJokj8MvB23i+KgfL9s2fF07ZtloHz25nGxCcw=; b=IbpaFlKpeA4JFZRTs7k4EM9meHM8rqNlkc7853eC6eHUK3DbIhaVDMxQ+fem+c4f+dtDuE y6OhZo3KMkn3mClYnfAZ9QXDmpNSTEDhd/MA7LJ4NycFEh2iQTAefbclmy+AYROQyxRBxf ornndC/2/V47wWEUo6ZTo1CKDrkwRGA= Date: Mon, 13 Jul 2026 21:28:10 +0800 MIME-Version: 1.0 Subject: Re: [PATCH v6 4/8] mm: add a template-based fast path for zone-device page init To: Li Zhe Cc: linux-arch@vger.kernel.org, linux-hardening@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org, akpm@linux-foundation.org, apopple@nvidia.com, arnd@arndb.de, balbirs@nvidia.com, bp@alien8.de, dave.hansen@linux.intel.com, david@kernel.org, kees@kernel.org, mingo@redhat.com, rppt@kernel.org, tglx@kernel.org References: <20260709112520.24857-1-lizhe.67@bytedance.com> <20260709112520.24857-5-lizhe.67@bytedance.com> Content-Language: en-US X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Muchun Song In-Reply-To: <20260709112520.24857-5-lizhe.67@bytedance.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspamd-Queue-Id: 622C02000E X-Rspam-User: X-Stat-Signature: 17ee4uqxnzemtqtfoygkm8reepqj8ady X-Rspamd-Server: rspam03 X-HE-Tag: 1783949302-773091 X-HE-Meta: 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 Ce/FQOXF AEv1M2537THdr2mA2D2vNBvBRwQSFX4PnaOwvCSBTD//vHWYv8y7wl/hZBsnx6CDuFAWNL0CRjXRgMssgi6vWH9fBXRLDH3BCNnTWfMcs44akXuZorwSwOrTyX9A3tg+izaYoIqLQWhKqZjYcUqClDpFaCu2gJvbubFDUqiQQnv148de4YEav/lrIxrNVQPF5XctwPc7nd92VS2ZIqDWJ/Y28rI9uS6Eszl0E9gNzv+ywboPY/l/wErfI8ZWPK0S9N031PZz7qR07dxs= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2026/7/9 19:25, Li Zhe wrote: > 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%. An 11% reduction is definitely a solid achievement. While the absolute gain is in the range of a few dozen milliseconds, I’d love to better understand the compounding impact. In which specific latency-sensitive scenarios or workloads does saving these few dozen milliseconds translate into a major breakthrough for the user experience? Muchun, Thanks. > > 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 5fccfbacf855..170021e182e0 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