From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from va-1-113.ptr.blmpb.com (va-1-113.ptr.blmpb.com [209.127.230.113]) (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 E2A102BDC13 for ; Thu, 21 May 2026 04:03:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.127.230.113 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779336231; cv=none; b=HoLldMMcTbsL9o/xngENj3xYn8LIB2cBLdIbaQgVYW05bfq1H3G47AxDhx5jA0eSOWaopYLBmGBEWAv+zmAD+ZMw+csih3hPyf392AWmllAa30qN1Ni47eHEuBJTIqxuXBGS3mU1ez+NZPrMzwm1b84YqSnzOj8J6MSGiRnFoA4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779336231; c=relaxed/simple; bh=TUt/dRvpfji4gx0lLQS6xlyPGQUGCXfNhUwSRyiuUKs=; h=From:Mime-Version:Subject:Date:In-Reply-To:To:Cc:References: Content-Type:Message-Id; b=JiQ8vIm1uVUcxLi8wi3UqrPDnkTyoCziR575SS/8xkJ33gRYDbwtNzDa3nPk4rVBRCPwm3Px7S/YFfsnnI3h9s7WhKo900J2XZvPllZMHLxlsZnAtdqiITKGlZX2/YmnypWzzR3j164Of4FD1gDPplj/hAT6ytb20LZ+cvBsWyU= 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=oP+cCJ8d; arc=none smtp.client-ip=209.127.230.113 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="oP+cCJ8d" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; s=2212171451; d=bytedance.com; t=1779336223; h=from:subject: mime-version:from:date:message-id:subject:to:cc:reply-to:content-type: mime-version:in-reply-to:message-id; bh=WzT6rgRltF1pu1V66u6WO6GZ1NJSxQBmJVnmonaqWWc=; b=oP+cCJ8dMsyfbEgYOTRLckiA3oy8+w1BUJHSGMskJ/XDSL48xyyYEZEQf3M4HukHjSZ+T1 H+2kwrHIeYpb/2RiUdGW5vsf7cuVF+/V+XjuG+OH3ZkqLtaNIiq3E6DpJn9/wPRpD9yvF4 sfhF6TBnKmHHyF1HT9naohF3VUdnBKc40YL5E/WV2919o7CYM7HD0Jrdg7U9BW0LqQAUZj 05oCLQ5Tp93LQoBDHFzOCCZP1vzTooGGnBsmbMqWwXK6H6/+5IB438uJDgjtdzKw6jOAtz JHtORZM6hhFoYnVTnUj8rS413VzCoO/a2ryL7LVaCoObJyFiVvxghZKHEmMZnA== Content-Transfer-Encoding: 7bit From: "Li Zhe" Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Subject: [PATCH v2 3/7] mm: add a template-based fast path for zone-device page init Date: Thu, 21 May 2026 12:01:20 +0800 In-Reply-To: <20260521040124.10608-1-lizhe.67@bytedance.com> X-Mailer: git-send-email 2.45.2 X-Original-From: Li Zhe To: , , , , , , , , , Cc: , , , , , References: <20260521040124.10608-1-lizhe.67@bytedance.com> Content-Type: text/plain; charset=UTF-8 Message-Id: <20260521040124.10608-4-lizhe.67@bytedance.com> X-Lms-Return-Path: 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, copy it into each destination page, and then fix up the PFN-dependent fields after the copy. The optimized path assigns _refcount through the copied template, so keep it disabled when the page_ref_set tracepoint is enabled. Also fall back to the slow path if struct page is not an integral number of u64 words. This patch accelerates the pfns_per_compound == 1 case. 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-rc3): First binding: 1486 ms Average of subsequent rebinds: 273.52 ms With patches 1-3 applied: First binding: 1422 ms Average of subsequent rebinds: 245.73 ms This reduces the average rebind time from 273.52 ms to 245.73 ms, or about 10%. Signed-off-by: Li Zhe --- mm/mm_init.c | 70 +++++++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 69 insertions(+), 1 deletion(-) diff --git a/mm/mm_init.c b/mm/mm_init.c index 4ba506df93bc..2992711351a0 100644 --- a/mm/mm_init.c +++ b/mm/mm_init.c @@ -1066,6 +1066,63 @@ static void __ref zone_device_page_init_slow(struct page *page, zone_device_page_init_pageblock(page, pfn); } +/* + * ZONE_DEVICE depends on MEMORY_HOTPLUG, and MEMORY_HOTPLUG is 64-bit + * only. That means CONFIG_ZONE_DEVICE cannot be enabled on 32-bit + * builds, so this fast-path code does not need a separate 32-bit + * fallback implementation. + */ +static inline bool zone_device_page_init_optimization_enabled(void) +{ + /* + * The template fast path copies a preinitialized struct page as an + * array of u64 words. Skip it when the page_ref_set tracepoint is + * enabled, and fall back to the slow path if struct page is not an + * integral number of u64 words. + */ + return !page_ref_tracepoint_active(page_ref_set) && + IS_ALIGNED(sizeof(struct page), sizeof(u64)); +} + +static inline void zone_device_template_page_init(struct page *template, + unsigned long pfn, + unsigned long zone_idx, + int nid, + struct dev_pagemap *pgmap) +{ + __zone_device_page_init(template, pfn, zone_idx, nid, pgmap); + if (!zone_device_page_init_refcount(pgmap)) + set_page_count(template, 0); +} + +/* + * The copied template already provides the PFN-invariant portion of a + * ZONE_DEVICE struct page. Fix up the fields that still depend on @pfn + * after the copy, namely the section bits and page->virtual when present. + */ +static inline void zone_device_page_init_finish(struct page *page, + unsigned long pfn) +{ + set_page_section_from_pfn(page, pfn); +#ifdef WANT_PAGE_VIRTUAL + if (!is_highmem_idx(ZONE_DEVICE)) + set_page_address(page, __va(pfn << PAGE_SHIFT)); +#endif +} + +static void zone_device_page_init_from_template(struct page *page, + unsigned long pfn, const struct page *template) +{ + const u64 *src = (const u64 *)template; + u64 *dst = (u64 *)page; + unsigned int i; + + for (i = 0; i < sizeof(struct page) / sizeof(u64); i++) + dst[i] = src[i]; + zone_device_page_init_finish(page, pfn); + 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 @@ -1114,6 +1171,7 @@ 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); @@ -1121,6 +1179,7 @@ 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; @@ -1135,10 +1194,19 @@ void __ref memmap_init_zone_device(struct zone *zone, nr_pages = end_pfn - start_pfn; } + if (use_template) + zone_device_template_page_init(&template, start_pfn, zone_idx, + nid, pgmap); + 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_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