From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from va-1-114.ptr.blmpb.com (va-1-114.ptr.blmpb.com [209.127.230.114]) (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 2836541D63A for ; Thu, 16 Jul 2026 11:57:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.127.230.114 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784203039; cv=none; b=bhhxEq/+qjX/FQaJqfhTaSYqzq60OvUcJGhXklsy/DThpIyNF/NCwbsMtm5BEtZAgxZ1jO7lCWdCLz6wb7msHkB2oEwvlvaC5a9l8AakxF7VM2LyRTBVrmK7qRMONxdbs7dt1P2XDfJS2+KGlawClrmcutZYjfA/v8VHciX7yFc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784203039; c=relaxed/simple; bh=Ta89MU67kAgoIbMPqRHVemmiq8uUBPzV0O1mGv8P4tw=; h=Message-Id:In-Reply-To:To:From:Subject:Date:Cc:Mime-Version: References:Content-Type; b=lqtki2yTNN+F+YaiqOCOFSxtxLqJLLQ6/Z7rFHWpBzxhmW19AJGNlfl6NohcmB3t40fDQ5jzH42O0kxZUijr2WF6ELd5/mzRsgep8BRrNKcY8H4jtjUPty2nRB9mK8J+UGMG6xxOB/T+677/Dh0vQkNWFtshL0vis5hACuD1Q6k= 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=AJNb6aDx; arc=none smtp.client-ip=209.127.230.114 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="AJNb6aDx" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; s=2212171451; d=bytedance.com; t=1784203032; h=from:subject: mime-version:from:date:message-id:subject:to:cc:reply-to:content-type: mime-version:in-reply-to:message-id; bh=w7po/hPV41ebN4SVCqHfXqnGtA3i/KcvpBhmzyD+bII=; b=AJNb6aDxv0WDBNphnYixnCKDK1hE4Ty1BsgmdMn7dK7QsFkTOIKivRtq98pkrHpQkPvrxT aaxPvQzU+nUQ6m/wPE26CNbqLye8mFIIGEKxwqyi4kwHIi3U7A60IXvFCpMisxDwCDnZ0b E9NQFZTy+uLnBjXlsCXbVo7nKa6+TqzzTMK5/+Q/lH/0FCunF28Je+Pazkx2bEZmmkvmb2 AQF61Ugp4RdgzjuBit/jH34f/U5IM+nqo2plwhDOciWjQupnakv8mdtjtm8MNr3kbHEi8+ v73qGNlLwWfCpux8Ym35wHIhN3mW8/3P4gC8orIG4whIqlAJMjHnMJSjvctiuA== Message-Id: <2e4ecb6f-4c9d-45b6-8ae1-3c165110c9ad@bytedance.com> In-Reply-To: <10E87709-2116-46E3-96E2-6BC4E6F69952@linux.dev> Content-Transfer-Encoding: 7bit To: "Muchun Song" From: "Li Zhe" Subject: Re: [PATCH v6 8/8] mm: use memcpy_nt() in zone-device template copies X-Lms-Return-Path: Date: Thu, 16 Jul 2026 19:56:48 +0800 User-Agent: Mozilla Thunderbird Cc: , , , , , , , , , , , , , , , Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260709112520.24857-1-lizhe.67@bytedance.com> <20260709112520.24857-9-lizhe.67@bytedance.com> <04f5b50a-a526-4644-b9f0-c54a0d6db702@linux.dev> <67BC9BE5-A201-4DED-B847-8C74BF30B16D@linux.dev> <10E87709-2116-46E3-96E2-6BC4E6F69952@linux.dev> X-Original-From: Li Zhe Content-Type: text/plain; charset=UTF-8 On 7/15/26 5:45 PM, Muchun Song wrote: > >> On Jul 15, 2026, at 14:30, Li Zhe wrote: >> >> On 7/14/26 7:22 PM, Muchun Song wrote: >>>> On Jul 14, 2026, at 17:45, Muchun Song wrote: >>>> >>>> >>>> >>>> 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. >>> BTW, If you really want to properly support KASAN, you should integrate >>> the check directly into memcpy_flushcache() via kasan_check_write(), rather >>> than treating it as a special case here. >> I agree that proper KASAN-aware support, if ever needed for >> memcpy_flushcache(), would belong in the low-level helper itself rather >> than in this caller. >> >> That said, for this series I would still prefer to keep the local check >> in zone_device_page_init_optimization_enabled(). The goal here is not to >> add full KASAN support to memcpy_flushcache(), but simply to keep >> sanitized builds on the existing instrumented slow path. >> >> When KASAN/KMSAN is enabled, performance is usually not the priority for >> that configuration, while preserving the instrumented store path is. >> Keeping the check local here avoids broadening the scope of this series >> into a generic memcpy_flushcache() change. > However, there is an even simpler approach: just don't do any special handling > for KASAN. In fact, many callers of memcpy_flushcache don't handle it at all. > > So I'm curious, why are you keen on handling KASAN as a special case here? > > Thanks. I agree that this is a simpler direction. If we do not need to keep the sanitizer case on the non-template path, then there is little value in keeping a separate zone_device_page_init_optimization_enabled() helper either. The template path can be the only initialization path, and the old non-template helper code can be removed. If this looks good to everyone, I plan to do that as a separate cleanup patch in the next version, likely as patch 9. The reason for keeping it separate is that patches 4 and 5 introduce the template initialization logic, while patch 8 only switches the copy primitive used by that path. Dropping the remaining non-template fallback is a follow-up cleanup made possible by this discussion, so a separate patch should make the change easier to review: first add and use the template path, then remove the now-unneeded fallback code. Thanks, Zhe >> Thanks, >> Zhe >> >>>> 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