From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 7A259412C04 for ; Thu, 24 Sep 2026 19:54:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790279665; cv=none; b=YB4QmVewg2yj3dqZg28j0+o8LZLC0/obYD61FnI0hyugYB9h38hbThmG78M0G3YHwgZgLXMzuoVnW37uozeI8M/FtNB8F55KDW+gkhmP103VPzEo+S+0HIbaoOruFkCLd9O0xhLQjofoLazLOef9gqVepdkjAMifwIPoGfA9LIM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790279665; c=relaxed/simple; bh=Xk735ReweqVrVn13Ui3Uv7zUhw3DLKK/ZBmVPDrpTFU=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=bOkw+JHALggF7eDXKBIsGXKRzBtb7AasgNMQXOZnK8+P5f0dxNtD7tVazsrSyDPsnkEcVttiG7l2DzPhpr2MxFRy7UkqgCeLOyUyX2d3fzkyOl6adXGvRHoqFZ9laZ2oKE1dqsikjsjGA+tWxzcY8AxIIEndbWiIegP9XQ9t/wQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Ue+9AbvB; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Ue+9AbvB" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2B13A1F000FF; Thu, 24 Sep 2026 19:54:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790279654; bh=0HJNKuMWG8smWqhbQSNH8vsLE/Fn0+yWkGNbv2CcO2E=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=Ue+9AbvBliMX+AIYWSvzQWUAHjFI3jdLOlYH/aiNY3rhxae13ZiGjmWsr8aJZNcpr MfQ1/lX8DbksvJiuh/nkNXdhKQe81Z2d8J4cm9YHvfu0c61XAOxufIl4bGlteKSYa8 3ZxGS5STiI1p6uzVLM6rQlB7RiVVJOjXfEvc4MfFDn0cZrc/5OGQij2Y5y8akxyKOt QrJ8ML2y4spobTgcJPcgtV+cNiAaLhG9i5cVWxzjvybQ87SHmd0fMDX5VkeYBwd8R7 VNVePZoQSbnizLpo3ctvplSR/tUOuDV4rK1BKVLcgMxf8plzTKyPdXN+oUImJ7G2wI SWj4KOKPH2BTQ== Message-ID: <25cae0dd-6b4b-4519-8119-231e2f65da46@kernel.org> Date: Thu, 24 Sep 2026 21:54:08 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 2/2] mm/memory: reuse the whole exclusive large folio on a write fault To: Yuan-Hao Hsu Cc: Andrew Morton , Lorenzo Stoakes , liam@infradead.org, Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Barry Song , Ryan Roberts , Dev Jain , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <0c0c19d0-997a-4c8d-a103-2b3d153f4e32@kernel.org> <20260919111851.678-1-aa9736195201@gmail.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/19/26 13:18, Yuan-Hao Hsu wrote: > On Sat, 19 Sep 2026 12:10:56 +0200, David Hildenbrand (Arm) wrote: >> Are you measuring the worst-case latency of a single write fault or only the >> average over all writes? > > The single fault. Each store is timed by itself (clock_gettime() > before and after), and the latency numbers come from a pattern where > every store takes one of these faults (one store per folio), so there > is nothing else in the average. The tables show the median of those > faults; I also have p99 and max (i7-12700KF, in a VM, us): > > v7.3-rc3+ patched > p50 p99 max p50 p99 max > 64K, 1 fault 0.42 0.57 25-26 0.71-0.74 0.96-1.10 28-60 > 2M, 1 fault 0.50 0.67 0.7-1.2 10.0-10.2 12.2-15.8 13-22 > > max is the slowest store of a run, median over 15 runs. The 25 us on > the base kernel are interrupts; the VM has those on both sides. The > 2M row is the worst case by construction, every one of those faults > walks all 512 PTEs. Thanks. See my other mail, we should focus on keeping the fault path as fast as possible and minimizing the work in there. -- Cheers, David