From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-119.freemail.mail.aliyun.com (out30-119.freemail.mail.aliyun.com [115.124.30.119]) (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 654631799F for ; Sat, 15 Nov 2025 00:49:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.119 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763167767; cv=none; b=qq6dNbA9/8r1VhQf/gxeem82FTkZGSBXsP3L7RcIeLB1yIoZwswfgYfFsQ6mhYGnJoZpXqSXxIWXBhFGKMjKqBHrD75p5NzjI+ZKRL9abMSrJa8jHB8pzrOH6n4nYHBcnuPlF3xJuLut0KmsPhlXOI/cDydKPwctQnZpa8genFk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763167767; c=relaxed/simple; bh=FZYrQqqMbPPHt5p6O4qxNBi+WP7LqSUttOKGmn9hGZo=; h=From:To:Cc:Subject:In-Reply-To:References:Date:Message-ID: MIME-Version:Content-Type; b=ggQVzT4tdmqvjOzLcjCvvNF/RbXlTcVrlD1YsX6KVGGVKeppvaHd/JnSkQ4ZfukCM1BijiL4sqaLxGz9fS1r+SUax7AgWYmvW6zPM7q7FiMPpCFJNdmd/ndWTViulS3QM4dBezFWRT1feSsP/+E6r+94aNS/QbmrhdkxP1ZNUTw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b=HFxIY/R6; arc=none smtp.client-ip=115.124.30.119 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b="HFxIY/R6" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1763167756; h=From:To:Subject:Date:Message-ID:MIME-Version:Content-Type; bh=htUByUHiQNU0PaaZJdOzX/xk7D/ge5gLRVLcI608Ows=; b=HFxIY/R6zaU+tEdfztmjxPmjAs/NjtHZmfF8J0i65XeYXWJ6J38OJKOxmyadiZtX/Zjvm3/pDcXrMy853WPt3cQtnrkMIOWF4TODHZu3cJb150x1RaNrxknDOxQvMdB9aL1azHz2C6dp+l811GvhIX7xmaC9/1OBUV9zc8L/u5c= Received: from DESKTOP-5N7EMDA(mailfrom:ying.huang@linux.alibaba.com fp:SMTPD_---0WsOJfMa_1763167753 cluster:ay36) by smtp.aliyun-inc.com; Sat, 15 Nov 2025 08:49:14 +0800 From: "Huang, Ying" To: "David Hildenbrand (Red Hat)" , Catalin Marinas , Will Deacon , Andrew Morton Cc: Ryan Roberts , Barry Song , Zi Yan , Lorenzo Stoakes , Vlastimil Babka , Baolin Wang , Yang Shi , "Christoph Lameter (Ampere)" , Dev Jain , Anshuman Khandual , Kefeng Wang , Kevin Brodsky , Yin Fengwei , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH -v6 2/2] arm64, tlbflush: don't TLBI broadcast if page reused in write fault In-Reply-To: <2bb9f0c2-a258-4a57-882e-9629f9cc81e6@kernel.org> (David Hildenbrand's message of "Fri, 14 Nov 2025 10:49:45 +0100") References: <20251114085403.101552-1-ying.huang@linux.alibaba.com> <20251114085403.101552-3-ying.huang@linux.alibaba.com> <2bb9f0c2-a258-4a57-882e-9629f9cc81e6@kernel.org> Date: Sat, 15 Nov 2025 08:49:12 +0800 Message-ID: <87pl9kf7cn.fsf@DESKTOP-5N7EMDA> User-Agent: Gnus/5.13 (Gnus v5.13) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=ascii "David Hildenbrand (Red Hat)" writes: > On 14.11.25 09:54, Huang Ying wrote: >> A multi-thread customer workload with large memory footprint uses >> fork()/exec() to run some external programs every tens seconds. When >> running the workload on an arm64 server machine, it's observed that >> quite some CPU cycles are spent in the TLB flushing functions. While >> running the workload on the x86_64 server machine, it's not. This >> causes the performance on arm64 to be much worse than that on x86_64. >> During the workload running, after fork()/exec() write-protects all >> pages in the parent process, memory writing in the parent process >> will cause a write protection fault. Then the page fault handler >> will make the PTE/PDE writable if the page can be reused, which is >> almost always true in the workload. On arm64, to avoid the write >> protection fault on other CPUs, the page fault handler flushes the TLB >> globally with TLBI broadcast after changing the PTE/PDE. However, this >> isn't always necessary. Firstly, it's safe to leave some stale >> read-only TLB entries as long as they will be flushed finally. >> Secondly, it's quite possible that the original read-only PTE/PDEs >> aren't cached in remote TLB at all if the memory footprint is large. >> In fact, on x86_64, the page fault handler doesn't flush the remote >> TLB in this situation, which benefits the performance a lot. >> To improve the performance on arm64, make the write protection fault >> handler flush the TLB locally instead of globally via TLBI broadcast >> after making the PTE/PDE writable. If there are stale read-only TLB >> entries in the remote CPUs, the page fault handler on these CPUs will >> regard the page fault as spurious and flush the stale TLB entries. >> To test the patchset, make the usemem.c from >> vm-scalability (https://git.kernel.org/pub/scm/linux/kernel/git/wfg/vm-scalability.git). >> support calling fork()/exec() periodically. To mimic the behavior of >> the customer workload, run usemem with 4 threads, access 100GB memory, >> and call fork()/exec() every 40 seconds. Test results show that with >> the patchset the score of usemem improves ~40.6%. The cycles% of TLB >> flush functions reduces from ~50.5% to ~0.3% in perf profile. >> Signed-off-by: Huang Ying >> Reviewed-by: Ryan Roberts >> Reviewed-by: Barry Song >> Acked-by: Zi Yan >> Cc: Catalin Marinas >> Cc: Will Deacon >> Cc: Andrew Morton >> Cc: David Hildenbrand >> Cc: Lorenzo Stoakes >> Cc: Vlastimil Babka >> Cc: Baolin Wang >> Cc: Yang Shi >> Cc: "Christoph Lameter (Ampere)" >> Cc: Dev Jain >> Cc: Anshuman Khandual >> Cc: Kefeng Wang >> Cc: Kevin Brodsky >> Cc: Yin Fengwei >> Cc: linux-arm-kernel@lists.infradead.org >> Cc: linux-kernel@vger.kernel.org >> Cc: linux-mm@kvack.org >> --- > > (no need to resend just for acks/rbs, maintainers can pick that up) Sure. > Reviewed-by: David Hildenbrand (Red Hat) Thank you David! Hi, Maintainers, I have collected some acks/rbs. What do you think about the patchset? What do I need to do for the next step? --- Best Regards, Huang, Ying