From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from va-2-113.ptr.blmpb.com (va-2-113.ptr.blmpb.com [209.127.231.113]) (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 59D093F4824 for ; Wed, 1 Jul 2026 09:06:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.127.231.113 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782896806; cv=none; b=ddRvY9rnVxX7mB1/+y90aWE8SVp64GxJd9FLajuzvt+gA7u7erHg2yoLE3FP5C7UVFELmPFODVthz6zRORUPKFZwC9OSm5nEM+QnMzyB+Zpi6iYsIIFa14EBg33afEXEf6MqN5BugkRX7NXq/RveoFF3nnAPcqb+k47hlguBMx8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782896806; c=relaxed/simple; bh=AnkOeZIxYVZ5Da140oXlC1j3YjOwdrXbGPhJRoHDG1k=; h=Date:Mime-Version:Message-Id:Cc:From:Subject:To:Content-Type; b=NeIdPrC2IMpyMJUHBCinhsJSz5mGmvwqMT+PV+uis6hq4ur9jKmq6IaNNFdw4fzpjzcd3zte8E9Nu0Rf20hwCe+/qB/+Z4vU1wnyXjRVgpEFJPasNaiagNIu3DHIVRBIeOrQ23AVzfdS59Mkrsb24SaX8GpiglP1Qis2ENgfbz8= 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=AUzTuqlX; arc=none smtp.client-ip=209.127.231.113 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="AUzTuqlX" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; s=2212171451; d=bytedance.com; t=1782896792; h=from:subject: mime-version:from:date:message-id:subject:to:cc:reply-to:content-type: mime-version:in-reply-to:message-id; bh=EjyWjEtrStwT/2+GI68sA9Nxt1WEmHQBHqN0cpYv9mI=; b=AUzTuqlXcRIm1fVH9G21uK/TvuhInTC43antstOtLIaofe7UDmyMxvQ275UzJEk68bXz3j 3osGYWwCSZQ5yEYJihOMfDd6/IJECLI6B4rQSaAds4Rc6AKAuTMOTTasqG93nrauRrNIvD ldZ7lhvbFvvaPx7MT1DundeGyNFy9tjY8CoTOTyEpWV5QxkcvKA4gEUoF3eMmIstc+ZglR XQ8YHnAmQdUSkQnaKMs7MIU4EBhWGnFfMY4DM4SCb/EEb5dVWUguBNmFQpLIbzFE2RcZIT KyXewqVz+CDL1tXqAE4z3LUXVEmRI/mn7CYA06Zq9OlSQ95y5y8nfuH9FjK1GA== Date: Wed, 1 Jul 2026 17:05:45 +0800 Precedence: bulk X-Mailing-List: linux-arch@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Message-Id: <20260701090553.62691-1-lizhe.67@bytedance.com> Cc: , , , , , From: "Li Zhe" Subject: [PATCH v5 0/8] mm: optimize zone-device memmap initialization X-Lms-Return-Path: X-Original-From: Li Zhe X-Mailer: git-send-email 2.45.2 To: , , , , , , , , , Content-Type: text/plain; charset=UTF-8 memmap_init_zone_device() can take a noticeable amount of time when large pmem namespaces are bound or rebound, because it initializes nearly identical struct page descriptors one PFN at a time. This series reduces that ZONE_DEVICE memmap initialization overhead by reusing prepared struct page templates and, on x86, using memcpy_nt() for the template copy path. The main target is large fsdax/devdax pmem configurations, where the cost of initializing the memmap shows up directly in nd_pmem/dax_pmem bind and rebind latency. Patches 1-3 are preparatory cleanups and helper extraction. Patches 4-5 add the template-copy fast path for head pages and compound tails. Patches 6-8 introduce memcpy_nt()/memcpy_nt_drain(), extend the x86 fixed-size memcpy_flushcache() inline cases used by that helper, and switch the template-copy path over to memcpy_nt(). The fast path remains disabled when the page_ref_set tracepoint is active, and sanitized builds stay on the slow path so their instrumented stores are preserved. Architectures without a specialized memcpy_nt() backend continue to fall back to memcpy(). 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 applied: 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. As an additional data point, I also ran a smaller set of measurements on the same physical x86_64 host with a 100 GB PMEM region created via the memmap= kernel command line, configured as fsdax and devdax namespaces with map=dev and 2 MiB alignment. For brevity, the individual patches keep only the VM results rather than including a second set of physical-host measurements throughout the series. The physical-host numbers below are included only as supplemental evidence that the same optimization also provides a similar benefit on a non-virtualized system. Test procedure: Reconfigure the namespace mode, rebind the nd_pmem or dax_pmem driver once, and collect the memmap initialization time from the pr_debug() output of memmap_init_zone_device(). Base (v7.2-rc1): nd_pmem / fsdax: 179 ms dax_pmem / devdax: 264 ms With this series applied: nd_pmem / fsdax: 82 ms dax_pmem / devdax: 113 ms This reduces the measured rebind time by about 54.2% for nd_pmem and 57.2% for dax_pmem on that setup, which is broadly consistent with the VM results above. As another supplemental data point, I also measured the test_hmm.ko module on the same physical x86_64 host, using the test_hmm.ko setup from the previous discussion that times ten 64 GB memremap_pages()/memunmap_pages() iterations during module insertion[1]. By default, module insertion initializes two DEVICE_PRIVATE dmirror devices, so two avg memremap values are reported; each value is the average for one 64 GB chunk. This is not the primary target workload of the series, but it exercises the same large ZONE_DEVICE memmap initialization path and shows the same direction of improvement. Base (v7.2-rc1): avg memremap reported during module insertion: 116689362 ns, 116539263 ns With this series applied: avg memremap reported during module insertion: 54607108 ns, 54458236 ns This corresponds to about a 53.2% reduction based on the mean of the reported values, which is again consistent with the pmem bind/rebind results above. [1] https://lore.kernel.org/all/aiEoByaQdRR3xtM5@nvdebian.thelocal/ Li Zhe (8): mm: fix stale ZONE_DEVICE refcount comment mm: factor zone-device page init helpers out of __init_zone_device_page mm: add a set_page_section_from_pfn() helper mm: add a template-based fast path for zone-device page init mm: extend the template fast path to zone-device compound tails string: introduce memcpy_nt() helpers x86/string: extend memcpy_flushcache() fixed-size fastpaths mm: use memcpy_nt() in zone-device template copies arch/x86/include/asm/string_64.h | 96 +++++++++++++- include/linux/mm.h | 19 ++- include/linux/string.h | 18 +++ mm/mm_init.c | 209 +++++++++++++++++++++++++++---- 4 files changed, 311 insertions(+), 31 deletions(-) --- v4: https://lore.kernel.org/all/20260603080152.64728-1-lizhe.67@bytedance.com/ v3: https://lore.kernel.org/all/20260527033636.28231-1-lizhe.67@bytedance.com/ v2: https://lore.kernel.org/all/20260521040124.10608-1-lizhe.67@bytedance.com/ v1: https://lore.kernel.org/all/20260515082045.63029-1-lizhe.67@bytedance.com/ Changelogs: v4->v5: - Rebase the series from v7.1-rc6 to v7.2-rc1, and refresh the VM performance numbers. - Simplify patch 6 around a small memcpy_nt()/memcpy_nt_drain() interface, rename the previous memcpy_streaming() helpers accordingly, make the generic implementation fall back to memcpy(), and let x86 reuse the existing memcpy_flushcache() backend instead of carrying extra policy/alignment logic in the generic layer. Suggested by Borislav Petkov. - Add physical-host measurements for a 100 GB PMEM region simulated via the memmap= kernel command line to the cover letter as supplemental evidence that the same optimization also improves fsdax/devdax map=dev bind/rebind latency outside the VM, while keeping the per-patch performance data limited to the VM measurements for consistency across the series. Suggested by Borislav Petkov. - Add supplemental test_hmm.ko results to the cover letter as another physical-host data point, in addition to the pmem bind/rebind measurements. v3->v4: - Rebase the series from v7.1-rc3 to v7.1-rc6. - Rework patch 4 so the reusable head-page template is seeded from the first real struct page, rather than being initialized directly on a stack-resident template object. Also add an explicit !nr_pages early return. Suggested by Andrew Morton. - Rework patch 5 similarly for compound tails: seed the reusable tail-page template from the first real tail page, thread use_template through compound-page initialization, and reuse that prepared tail-page image for the remaining tails. Suggested by Andrew Morton. - Tighten patch 6 so memcpy_streaming() maps to memcpy_flushcache() only when the destination alignment and size allow the transfer to stay entirely on the non-temporal path; other cases fall back to memcpy(). Suggested by Andrew Morton. - Rework patch 7 so the existing 4/8/16-byte cases remain handled directly in memcpy_flushcache(), while the new aligned fixed-size fastpaths cover only the larger 32/48/64/80/96-byte cases. Suggested by Andrew Morton. For changelogs of earlier revisions, please refer to the v3 cover letter: https://lore.kernel.org/all/20260527033636.28231-1-lizhe.67@bytedance.com/ -- 2.20.1