From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from va-1-113.ptr.blmpb.com (va-1-113.ptr.blmpb.com [209.127.230.113]) (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 3C58B37C903 for ; Fri, 22 May 2026 07:50:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.127.230.113 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779436203; cv=none; b=KyzAVzJcQUJNxSxqjDGQkNYFqofSm3JIvX9XMMSg+uPmCdElICt64CZQoqBZvjwgS36zrx0nWCxr45rYabhjMrtX+2L5ab4Zb0SBJtTBiIHh1/8qyQXE4kw1bqhxzFi/9KAFPppJYxNsn9+4utSlZhKGhL3wHayA9eHHcQPijI8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779436203; c=relaxed/simple; bh=X/hE1hO5sXT4ISKIuKrabgqu5qItUGb56mOAjmd/23U=; h=Subject:From:In-Reply-To:Cc:Message-Id:Content-Type:To:Date: Mime-Version:References; b=hiJT0VgPUOOX3oKnRvvWXgN4Oi/KaZ7PcO4hbZnZQe6QCLEXUPWM/rcJgd9a9n+ZgIwAwQl5KZNyKlL/lmMrYoBtEyWTgaPbTkcs1p7Z9Pkg+VfJbUeqdLiuNb3CdfWThGkd4HH/hu2JhIOJ/CgIix6yxl9/4Kabyg9Vv16kw2s= 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=K4og7kt6; arc=none smtp.client-ip=209.127.230.113 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="K4og7kt6" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; s=2212171451; d=bytedance.com; t=1779436195; h=from:subject: mime-version:from:date:message-id:subject:to:cc:reply-to:content-type: mime-version:in-reply-to:message-id; bh=jxcBqSnTE8QGLvd7k0gAZTQfr15WCN3mLt1C6micdAg=; b=K4og7kt6gqblM70j41+tGVQJtYFeVHKvs0SxYRG2ebey1g1B3UGZV5qIjonVsEn/Bwcy6J T9Bc2bqdSdBUo+IQH5wiSwiaj3Yt99ysGcdGqZ9arezu/8sTEBu06CJ1JP8MJ24Rw+GoqW Ju3mddrydUeKNbVneT0dKWJbJav3IYRHrkgpcwE5Ilwli5XsTZydpv57I+w3KeH/Hbc01K lpULAtHWxnJb6HeYEVi6JqGZZ4bjtODp6D08ATU4uS8Upyp4xJ//bL2qAG2Y65/3mroxbo rqBtD2zxNDTjLkdtBNNKkZmMVZiQTVhT6rppm3L6alIGh920CNdrL2OPlfEksg== Subject: Re: [PATCH v2 0/7] mm: speed up ZONE_DEVICE memmap initialization X-Mailer: git-send-email 2.45.2 From: "Li Zhe" In-Reply-To: <20260521152029.4299697d40ddc58c721bbafd@linux-foundation.org> Cc: , , , , , , , , , , , , , , Message-Id: <20260522074932.62311-1-lizhe.67@bytedance.com> X-Original-From: Li Zhe Content-Type: text/plain; charset=UTF-8 X-Lms-Return-Path: To: Date: Fri, 22 May 2026 15:49:32 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260521152029.4299697d40ddc58c721bbafd@linux-foundation.org> Content-Transfer-Encoding: 7bit On Thu, 21 May 2026 15:20:29 -0700, akpm@linux-foundation.org wrote: > On Thu, 21 May 2026 12:01:17 +0800 "Li Zhe" wrote: > > > memmap_init_zone_device() can spend a substantial amount of time > > initializing large ZONE_DEVICE ranges because it repeats nearly > > identical struct page setup for every PFN. > > > > This series reduces that overhead in seven steps. > > Cool, thanks, we all love speedups. > > > The first patch factors the reusable pieces out of > > __init_zone_device_page() so later patches can share the same logic > > without changing the existing slow path. > > > > The second patch adds set_page_section_from_pfn(), so generic callers > > can update section bits from a PFN without open-coding > > SECTION_IN_PAGE_FLAGS checks. > > > > The third patch adds a template-based fast path for ZONE_DEVICE head > > pages. Instead of rebuilding the same struct page state for every PFN, > > it prepares a reusable page template once and copies it to each > > destination page. > > > > The fourth patch extends the same template-based approach to compound > > tails, so pfns_per_compound > 1 can also benefit from the fast path. > > > > The fifth patch introduces memcpy_streaming() and > > memcpy_streaming_drain() as a generic interface for write-once > > streaming copies, with a memcpy() fallback for architectures that do > > not provide a specialized backend. > > > > The sixth patch extends x86 memcpy_flushcache() small fixed-size > > fastpaths so struct-page-sized streaming copies can stay on the inline > > path. > > > > The last patch switches the zone-device template-copy path over to > > memcpy_streaming(). It refreshes PFN-dependent fields in the reusable > > template before each copy, keeps pageblock-aligned PFNs on regular > > memcpy(), and drains streaming stores before later normal stores update > > overlapping or dependent metadata. > > > > The optimized path is disabled when the page_ref_set tracepoint is > > enabled, sanitized builds remain on the slow path so their > > instrumented stores are preserved, and the fast path falls back to the > > existing slow path if sizeof(struct page) is not an integral number of > > u64 words. > > > > Testing > > ======= > > > > Tests were run in a VM on an Intel Ice Lake server. > > > > Two PMEM configurations were used: > > - a 100 GB fsdax namespace configured with map=dev, which exercises > > the nd_pmem rebind path (pfns_per_compound == 1) > > - a 100 GB devdax namespace configured with align=2097152, which > > exercises the dax_pmem rebind path (pfns_per_compound > 1) > > > > For each configuration, the corresponding driver was unbound and > > rebound 30 times. Memmap initialization latency was collected from the > > pr_debug() output of memmap_init_zone_device(). > > > > The first bind is reported separately, and the average of subsequent > > rebinds is used as the steady-state result. > > How closely does this workload resemble any real-world user workload? Not directly. The unbind/rebind loop is mainly a controlled and repeatable way to measure the memmap_init_zone_device() path with minimal unrelated noise. > > Performance > > =========== > > > > nd_pmem rebind, 100 GB fsdax namespace, map=dev > > Base(v7.1-rc3): > > First binding: 1486 ms > > Average of subsequent rebinds: 273.52 ms > > With patches 1-3 applied: > > First binding: 1422 ms > > Average of subsequent rebinds: 245.73 ms > > Full series: > > First binding: 1389 ms > > Average of subsequent rebinds: 111.08 ms > > > > dax_pmem rebind, 100 GB devdax namespace, align=2097152 > > Base(v7.1-rc3): > > First binding: 1515 ms > > Average of subsequent rebinds: 313.45 ms > > With patches 1-4 applied: > > First binding: 1422 ms > > Average of subsequent rebinds: 256.56 ms > > Full series: > > First binding: 1294 ms > > Average of subsequent rebinds: 110.24 ms > > The improvements appear to range between "modest" and "large", but what > I'd like to understand is how frequently real-world users are using > these operations in real-world workloads. > > IOW, (and this is always the bottom line), how valuable is this > patchset to our users? This is not a steady-state data-path optimization. Its value is in pmem bring-up paths, and in our deployment we do have scenarios where multiple pmem devices are hotplugged , so reducing this latency is useful in practice for us. > > 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_streaming() helpers > > x86/string: extend memcpy_flushcache() fixed-size fastpaths > > mm: use memcpy_streaming() in zone-device template copies > > > > arch/x86/include/asm/string_64.h | 100 +++++++++++++--- > > include/linux/mm.h | 19 ++- > > include/linux/string.h | 18 +++ > > mm/mm_init.c | 198 +++++++++++++++++++++++++++---- > > 4 files changed, 294 insertions(+), 41 deletions(-) > > I won't take any action at this stage - let's await reviewer input. If > none is forthcoming then please remind me and I'll figure out what to > do. > > The ever-present reviewer called "Sashiko" has thoughts to offer: > > https://sashiko.dev/#/patchset/20260521040124.10608-1-lizhe.67@bytedance.com > > Please take a look, decide if there's useful material in there. There is useful material there, mainly around patches 5 and 6. The memcpy_streaming() x86 backend should be narrower, and the expanded memcpy_flushcache() small-copy fastpath should keep naturally aligned cases only and preserve forward movnti store order. I'll address those points in the next revision and rerun the benchmarks. Thanks, Zhe