From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-178.mta0.migadu.com (out-178.mta0.migadu.com [91.218.175.178]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id DD6763F075A; Tue, 14 Jul 2026 09:45:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.178 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784022331; cv=none; b=i+E6sUCxD0G6gj03RqRSzS1gLSs/Ubj9BtefsZ9NBqF+UmLk5RozuHbrxBl63IXGdVBFiyO4GOG3lY4Qkq9g3oGA66Sut6UOyJl8B+bLBktb3ds0Zw8nQYea2I3eGPc+VZ7r+TZnb5oR6FSnXYeSLxQJsbO5WJM8bCL4VdP26ko= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784022331; c=relaxed/simple; bh=gcD0aYAmdIDfX+o5qeVTzlWkMrJJjaaRQvytk9PwmNk=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=RhaKb+vFizh6HPb/INiIqAzkGdv86Bhs4Pv15ruVzz2ofc4Kzoxhx83yPB5DxW45dYaL3RKEdTqTrnY88SeohoAiaBs8SmX5V5skB8IWwW6hqr8BWYk0kiAJN5b4lYFyLDx23wEcjWMyh3/0GlE0H9ESTk20mcmhwD6D+h2Gnp4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=s2kVBwVl; arc=none smtp.client-ip=91.218.175.178 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="s2kVBwVl" Message-ID: <04f5b50a-a526-4644-b9f0-c54a0d6db702@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1784022323; 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=mekORx+dFKRiABrAy+XEgciHwWSjZPvElZQGPDy01aI=; b=s2kVBwVl7nJQg4Gb/Kqxo1bPGuZQp8vx9e/9dh096WOea1GmNZvCyunI+kd7T22YqJYDA/ NKH2dTJV7HWZL661cCIPgju0vw80HFbKnXFteGddtiUZO3JDANIoYLOYb9ukTtCzgsEIpr nc7fRXOdZErHcdm3A2EnLN4UvV7I5T4= Date: Tue, 14 Jul 2026 17:45:17 +0800 Precedence: bulk X-Mailing-List: linux-arch@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH v6 8/8] mm: use memcpy_nt() in zone-device template copies 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> <20260709112520.24857-9-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: <20260709112520.24857-9-lizhe.67@bytedance.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT On 2026/7/9 19:25, Li Zhe wrote: > 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; It is not a major concern if struct page initialization lacks KASAN or KMSAN instrumentation. To keep things simple, let's just entirely remove zone_device_page_init_optimization_enabled() to simplify the code. Thanks. > + > /* > * 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 >