From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from va-2-112.ptr.blmpb.com (va-2-112.ptr.blmpb.com [209.127.231.112]) (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 9F85039D6C9 for ; Mon, 3 Aug 2026 07:13:10 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.127.231.112 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785741193; cv=none; b=uGKchnHDEAKGdbWx3kOfX4zD5Ti5pPrI3b7Lb7LIl5/t910zRy8J+7l4SXCNWAfZmUOBZyqEHXZixHjvyrtesRE8ERS3CTIlH7yKW44MpKxjCVy8fVdcR0gBftXUMEy5C1YMhvmwB37OQ6rXVAajrjeKf6qpTW5QbFAhMSOL72A= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785741193; c=relaxed/simple; bh=DIf+MYJmJLsTk693QI8cPlBfvGaOnDkShI8XUbuFBoE=; h=Subject:Date:Content-Type:To:Cc:Mime-Version:References: In-Reply-To:From:Message-Id; b=WyWGBjiWZkQhMxoGLV54IT+xycJTjDxb37lQl0f3JGDY12SksJPY5C1iEcxbTLbqEpDeUMP47oTQBdNlsYPjI9AMdHejZOenmA/FHbKMpJMYMSiN8mzxtaHNyixWRi0Yz3ZqKJCqLgX/NMELDRcqRjPQrFVk7+O8rdMyqqu0diY= 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=WkcGbKa4; arc=none smtp.client-ip=209.127.231.112 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="WkcGbKa4" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; s=2212171451; d=bytedance.com; t=1785741186; h=from:subject: mime-version:from:date:message-id:subject:to:cc:reply-to:content-type: mime-version:in-reply-to:message-id; bh=noN9zN1awgD10Dy4RdMcJEDTTzNu8MQNGVp8sfEJ5vA=; b=WkcGbKa4CmwS281FbN5fIMHqIcxeSwUbxp5n6Uy16IA+wlkHSVjbXYYyKYCsIZ3LGOrWuq ydQY3ixL2zS8N2nAeKNdLDRSyaMFuLkbDE4a5909M0TTZhTStcHFL5rgIxBpCcrg61gOHS GMosYi9rlv/uvcimlNstcDfbRYQ1wbmkfKHGZ+qncu1qGkKsLajWVV6UR5tauN8onneh79 UyT3w6XGESe8TQHsl1CrwhWgr4jfMUORfqLvu+v6aGOO50ePz9ktMRFt8jar6a4C8veh5K 0IrCfFM4rA98WFkr/KfuRaXq+crjhDQK6F4RIvY8NQhkSNV0lnot6um9ApQA1Q== X-Original-From: Li Zhe X-Lms-Return-Path: Subject: [PATCH v9 7/8] mm: use memcpy_nontemporal() in zone-device template copies Date: Mon, 3 Aug 2026 15:09:28 +0800 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=UTF-8 To: , , , , , , , , , , , Cc: , , , , , Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260803070929.86075-1-lizhe.67@bytedance.com> In-Reply-To: <20260803070929.86075-1-lizhe.67@bytedance.com> X-Mailer: git-send-email 2.45.2 From: "Li Zhe" Message-Id: <20260803070929.86075-8-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_nontemporal(). 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_nontemporal() lets this path request nontemporal 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(). Do not add a KASAN/KMSAN-specific fallback around this call site. As Muchun pointed out, special KASAN handling for memcpy_flushcache() or memcpy_nontemporal(), if needed, belongs in the low-level helper rather than in this ZONE_DEVICE caller. No separate drain is added here. memcpy_nontemporal() is used only as the copy primitive while memmap_init_zone_device() is still initializing the struct page array. The ordinary stores that follow in this path, such as compound-page setup, are part of the same CPU's initialization sequence; they are not used as a publication store that tells another CPU or device to consume data written by the non-temporal copy. Therefore this call site does not need a helper-level drain for correctness. Callers that use memcpy_nontemporal() as part of a producer-consumer or device-visible handoff must add the required ordering themselves. 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): Average of rebinds for nd_pmem driver: 244.28 ms Average of rebinds for dax_pmem driver: 273.31 ms With this patch and its prerequisites applied: Average of rebinds for nd_pmem driver: 150.83 ms Average of rebinds for dax_pmem driver: 153.55 ms This reduces the average memmap initialization time measured during rebind by about 38.3% for nd_pmem and 43.8% for dax_pmem. Signed-off-by: Li Zhe --- mm/mm_init.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/mm_init.c b/mm/mm_init.c index 9691fa2a060d..bb2007806a28 100644 --- a/mm/mm_init.c +++ b/mm/mm_init.c @@ -1101,7 +1101,7 @@ 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_nontemporal(page, template, sizeof(*page)); } /* -- 2.20.1