From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from va-2-114.ptr.blmpb.com (va-2-114.ptr.blmpb.com [209.127.231.114]) (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 06A3540BCDD for ; Thu, 9 Jul 2026 11:28:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.127.231.114 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783596534; cv=none; b=Re+WywM88AJGzJeT9ARAAel0vRffw3mCRRcPLHtMTdKBb5bn401RrH/W/72/LCcZs5LimTqy/zXOxOe30+uTWseP6OXWceC9+tD0tU8lEEvaIp6qrXN4vy9b41sTNc+FGDSFxWdGNcD1VXiGRpCjbRUVOp+4b7o3T5rcW2yPkHo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783596534; c=relaxed/simple; bh=j950b+jkxnNMvrl29X1CJHyRzGrjQn2bn3MzFAZQt4c=; h=From:In-Reply-To:Content-Type:Cc:Date:Mime-Version:To:Subject: Message-Id:References; b=Terzf/IaGUYEj+07dssr+gW4NZ/Yv+9poQCn0kL7+KSwRRi/K56wGFKxDyl+mF0qziIzPDFMJDoYjmWuhiUDmzNUT9LS8adQBWwbss7hfa3vbBZD0zTO+SXdMX13iA2zENU85yiIpOyweGxkoXCUlk91MV0fkRuJd/Xo+l/8zCg= 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=kwKIzdWJ; arc=none smtp.client-ip=209.127.231.114 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="kwKIzdWJ" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; s=2212171451; d=bytedance.com; t=1783596527; h=from:subject: mime-version:from:date:message-id:subject:to:cc:reply-to:content-type: mime-version:in-reply-to:message-id; bh=UJcKYOJQhKyg/isyMbMzrX1li+G0ZF58QSuW2HC410c=; b=kwKIzdWJAlIq6wGx8BgDz//6S0ckbT7x52bNr5qRL0mAfXe5FUrk8K9jV+vJ3GqcG4QqNl awQbHDCeAcBw6PVa2QXO+v+9fF9hLg8OG2k9ymylKNLVUi6HZxMmky1oJCkeMcdK7ICds7 GMpURhN7E5wXZtnKxZLpdPTApnCrn9B0yNt8fnIRAQ/+gp0zaYtk2/2OpVJGr64G18vzz8 n7lnAFIsCwyTQBI0Q3WDVetpP+4Gb9/ZA0k3Ot3MMNIK4l1EF9ieN7BsZ5uOcAtUW9SgzX u9aX5GEflM9TfqtonNut8gyMXmGW7QIFpkUuyi/PzBPhY8yhEsIaRQomO9AYaw== From: "Li Zhe" In-Reply-To: <20260709112520.24857-1-lizhe.67@bytedance.com> X-Mailer: git-send-email 2.45.2 Content-Type: text/plain; charset=UTF-8 Cc: , , , , , Date: Thu, 9 Jul 2026 19:25:20 +0800 X-Original-From: Li Zhe Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Transfer-Encoding: 7bit X-Lms-Return-Path: To: , , , , , , , , , , Subject: [PATCH v6 8/8] mm: use memcpy_nt() in zone-device template copies Message-Id: <20260709112520.24857-9-lizhe.67@bytedance.com> References: <20260709112520.24857-1-lizhe.67@bytedance.com> The template fast path currently uses memcpy() for the actual struct page copy. Switch zone_device_page_init_from_template() to memcpy_nt() and add memcpy_nt_drain() before memmap_init_compound(), before prep_compound_head() updates overlapping tail metadata, and before returning from memmap_init_zone_device(). ZONE_DEVICE memmap initialization is largely write-once: each struct page is populated once, and most destination cachelines are not expected to be reused immediately afterwards. On x86, a regular cached memcpy() can therefore incur write-allocate traffic by pulling destination cachelines into the cache before writeback, and can populate the cache with data that has little near-term reuse. Using memcpy_nt() lets this path request non-temporal stores for that copy pattern, which can reduce cache pollution and avoid part of the associated write-allocate overhead, while architectures without a specialized backend still fall back to memcpy(). When memcpy_nt() maps to non-temporal stores, order those stores before memmap_init_compound(), before prep_compound_head() updates overlapping compound metadata, and before returning from memmap_init_zone_device(). Keep sanitized builds on the slow path so KASAN/KMSAN retain their instrumented stores. Tested in a VM with a 100 GB fsdax namespace device configured with map=dev and a 100 GB devdax namespace (align=2097152) on Intel Ice Lake server. Test procedure: Rebind the nd_pmem and dax_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 for nd_pmem driver: 1456 ms Average of subsequent rebinds: 244.28 ms First binding for dax_pmem driver: 1462 ms Average of subsequent rebinds: 273.31 ms With this series: First binding for nd_pmem driver: 1272 ms Average of subsequent rebinds: 96.79 ms First binding for dax_pmem driver: 1354 ms Average of subsequent rebinds: 119.04 ms This reduces the average rebind time by about 60.4% for nd_pmem and 56.4% for dax_pmem. Signed-off-by: Li Zhe --- mm/mm_init.c | 39 +++++++++++++++++++++++++++++++++++++-- 1 file changed, 37 insertions(+), 2 deletions(-) diff --git a/mm/mm_init.c b/mm/mm_init.c index fb855bb0437a..addb4969587e 100644 --- a/mm/mm_init.c +++ b/mm/mm_init.c @@ -1067,11 +1067,21 @@ static void __ref zone_device_page_init_slow(struct page *page, static inline bool zone_device_page_init_optimization_enabled(void) { + /* + * Keep sanitized builds on the slow path so their stores stay + * instrumented. + */ + if (IS_ENABLED(CONFIG_KASAN) || IS_ENABLED(CONFIG_KMSAN)) + return false; + /* * 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); + if (page_ref_tracepoint_active(page_ref_set)) + return false; + + return true; } static inline void zone_device_tail_page_init(struct page *page, @@ -1110,7 +1120,7 @@ static void zone_device_page_init_from_template(struct page *page, * to the destination page. */ zone_device_page_update_template(template, pfn); - memcpy(page, template, sizeof(*page)); + memcpy_nt(page, template, sizeof(*page)); } /* @@ -1179,6 +1189,15 @@ static void __ref memmap_init_compound(struct page *head, &template); } } + + /* + * When the template path is enabled, order the preceding tail-page copies + * before prep_compound_head() updates the overlapping compound metadata + * in the first tail-page descriptors. If memcpy_nt() fell back to + * regular cached stores, memcpy_nt_drain() may be a no-op. + */ + if (use_template) + memcpy_nt_drain(); prep_compound_head(head, order); } @@ -1238,10 +1257,26 @@ void __ref memmap_init_zone_device(struct zone *zone, if (pfns_per_compound == 1) continue; + /* + * When the template path is enabled, order the preceding head-page copy + * before memmap_init_compound(), which immediately updates compound-head + * metadata. If memcpy_nt() fell back to regular cached stores, + * memcpy_nt_drain() may be a no-op. + */ + if (use_template) + memcpy_nt_drain(); + memmap_init_compound(page, pfn, zone_idx, nid, pgmap, compound_nr_pages(pfn, altmap, pgmap), use_template); } + /* + * Ensure any prior template copies are ordered before returning. + * On architectures where memcpy_nt() used regular cached stores, + * memcpy_nt_drain() may be a no-op. + */ + if (use_template) + memcpy_nt_drain(); pageblock_migratetype_init_range(start_pfn, nr_pages, MIGRATE_MOVABLE); -- 2.20.1