From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (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 B23861C5D55 for ; Sat, 16 Aug 2025 06:40:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755326446; cv=none; b=Fm5d350h+/I/57FEsZpFA439BZqEgEadhbucIFRGPmDq3r5BsNPHMNYY9D7AbSEHozjuAYQuSwuYs+3kz5AGsu1wEzffN0Ae+U+QkzntWJTfbg8HTr6tesSjTyuhDXLzndSoRIV2BUyPSn720aFy8aV0XdTrOnnfCaswmJa4hB0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755326446; c=relaxed/simple; bh=8819TNuNd8r7bptkuhT35C6lvo1jQWJLHOSTX4hEAkA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=uCTXyFQlARhm7X3qncj5e879TdcIxb/gj8MC/y2hJjYGxKdYBgxbECD0tH/6uwVp1CTwsI9jZ4mtheRYMZ4e3xX0bJ7+htblO8LU0EAUbmOFfIwQYBfOuLfD4PRonGr6ofTBrF1v/i+HaxIP6gxU6ZEMWqMVxZY0tiWpgp85bMU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=MkfFOXav; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="MkfFOXav" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1755326443; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:autocrypt:autocrypt; bh=jpRMVDaaLqCDMC4grBCrsBXEgRiflpzfM+Z/fw5Kj/s=; b=MkfFOXavwjY4PreLhz3s2ESeaBCw0MRbdnv5fo7Nmt1gWouxJYfzGqQSSmlU9A8Gv4wg+e K0rb2lCNyTleqZIPgIKCo4wEQ3nVi7tK+YhxpAVUQVqxiWmWZfELlmvDgzFCl5vAUjrX9u I/xDwGjD1aLwQ65nn1Q1InBavlKTcMk= Received: from mail-wm1-f69.google.com (mail-wm1-f69.google.com [209.85.128.69]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-14-PjGbqk2KOLOA8qKvJ6T3PA-1; Sat, 16 Aug 2025 02:40:41 -0400 X-MC-Unique: PjGbqk2KOLOA8qKvJ6T3PA-1 X-Mimecast-MFC-AGG-ID: PjGbqk2KOLOA8qKvJ6T3PA_1755326441 Received: by mail-wm1-f69.google.com with SMTP id 5b1f17b1804b1-45a1b05b15eso17786945e9.1 for ; Fri, 15 Aug 2025 23:40:41 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1755326440; x=1755931240; h=content-transfer-encoding:in-reply-to:autocrypt:content-language :from:references:cc:to:subject:user-agent:mime-version:date :message-id:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=jpRMVDaaLqCDMC4grBCrsBXEgRiflpzfM+Z/fw5Kj/s=; b=uaTVmMXRYsSCtVvjRN1xRZz1clql+BkfAdR0G4996jwmP5NQ1tCV6q//GKleVkZh22 wviZrMwnSJei6J2FCpaiwzqmHKA50Dp47F2se2OSnIfXsPpOOBPCT40HkpXssil3yHft uSZ78vQ6PZKIAlsXT+jArR/6IdhtfXGpZ84Orc48tp66YQ8AcIakmB50xU7Nl393J228 fGkty7Z9NIvrpLIwepx6FeoEXXBbLBDme2m3KGMA87BxCkaUwUFzvj9zLKfeJomFEFIB PDzkhBeatvnVlqXdQ4LhmgPFXYbNHFDWylWrvW4pLImEIs3MH/BONHggu7opaL++A23q IjuA== X-Forwarded-Encrypted: i=1; AJvYcCW0qe0jvIRW7ywd+Hs274MP+GC9M7kvD6x7KM+3LVh56cyYxZZaUcWm3cL9aBab83OSVlO6ygwwc+EUiHQ=@vger.kernel.org X-Gm-Message-State: AOJu0YwsjiZMe6fURQM1J/TwcHKxpnb/IGYG4y0EW4FRwtXebQwagV5/ +LjO95emrKAv1+X6PV4iiz7YS/ww3sipjuFqHpIwTzPES0by2lHul2nOaFSrCRIVVsrm1WqEa2H nyiVTfE3PcElAkKSHntSE66uif93SkWFr+ay/VOEljHy/SddZb1cbRDX8aXVuWHLTFA== X-Gm-Gg: ASbGnctnU9/f/8Mh/TL9vCRYoialtqJv+t/sPAfrExxpDiJWAM5DFG5cZjE3YeIWlKz t4/5Wdwo+Bx5ZBf7VjQilldyPk2ewtYka7G0OEDo3lz6T3lnJJLxYygGTHXS2ph5P8MbJy43YDf rpFuwJyfM2odLPbD4UORLjMnp6YtqQ+/s1sGNDG+/VQRMMvFOAHHvTBWVn+sxf1sB4rDnX4TdxG RujlsV2HZCBh5FiDb4FYcGBd9IHulQKnwumGjlJx+yN8SaBn9+KkYcNNzM72POKgn49idOfPdnV b578NisozYwUVal7Kl+lbuzKUB1rYXwZhMK7BP/mVzkPoBPtnW1jp/Fu+UTX3fMbJyIk3Yk2MDs +AcRlCf2jh4cANXz3w9xsmrGK22unqEyXbyPCrp0VlvoQGEbTPZSkFHPAlBLgjfYDsjM= X-Received: by 2002:a05:600c:4ecb:b0:43c:f8fe:dd82 with SMTP id 5b1f17b1804b1-45a2677e60amr10342615e9.18.1755326440292; Fri, 15 Aug 2025 23:40:40 -0700 (PDT) X-Google-Smtp-Source: AGHT+IEpfUkhjb1UsDmaY7WU/zF1Z7iPtlNuRIErvYfv3ZUEuiVzH0icWl5g9qcQkZoeYwyzg2Na9Q== X-Received: by 2002:a05:600c:4ecb:b0:43c:f8fe:dd82 with SMTP id 5b1f17b1804b1-45a2677e60amr10342355e9.18.1755326439560; Fri, 15 Aug 2025 23:40:39 -0700 (PDT) Received: from ?IPV6:2003:d8:2f23:c700:d8ae:41bf:492a:9e4c? (p200300d82f23c700d8ae41bf492a9e4c.dip0.t-ipconnect.de. [2003:d8:2f23:c700:d8ae:41bf:492a:9e4c]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-45a22210ab4sm44725805e9.3.2025.08.15.23.40.37 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 15 Aug 2025 23:40:38 -0700 (PDT) Message-ID: Date: Sat, 16 Aug 2025 08:40:37 +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: [RFC PATCH 6/7] mm: memory: add mTHP support for wp To: Vernon Yang Cc: akpm@linux-foundation.org, lorenzo.stoakes@oracle.com, ziy@nvidia.com, baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, glider@google.com, elver@google.com, dvyukov@google.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, muchun.song@linux.dev, osalvador@suse.de, shuah@kernel.org, richardcochran@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20250814113813.4533-1-vernon2gm@gmail.com> <20250814113813.4533-7-vernon2gm@gmail.com> <226e21a5-8a8e-43a0-bf5f-12a761f49a27@redhat.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZoEEwEIAEQCGwMCF4ACGQEFCwkIBwICIgIG FQoJCAsCBBYCAwECHgcWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaJzangUJJlgIpAAKCRBN 3hD3AP+DWhAxD/9wcL0A+2rtaAmutaKTfxhTP0b4AAp1r/eLxjrbfbCCmh4pqzBhmSX/4z11 opn2KqcOsueRF1t2ENLOWzQu3Roiny2HOU7DajqB4dm1BVMaXQya5ae2ghzlJN9SIoopTWlR 0Af3hPj5E2PYvQhlcqeoehKlBo9rROJv/rjmr2x0yOM8qeTroH/ZzNlCtJ56AsE6Tvl+r7cW 3x7/Jq5WvWeudKrhFh7/yQ7eRvHCjd9bBrZTlgAfiHmX9AnCCPRPpNGNedV9Yty2Jnxhfmbv Pw37LA/jef8zlCDyUh2KCU1xVEOWqg15o1RtTyGV1nXV2O/mfuQJud5vIgzBvHhypc3p6VZJ lEf8YmT+Ol5P7SfCs5/uGdWUYQEMqOlg6w9R4Pe8d+mk8KGvfE9/zTwGg0nRgKqlQXrWRERv cuEwQbridlPAoQHrFWtwpgYMXx2TaZ3sihcIPo9uU5eBs0rf4mOERY75SK+Ekayv2ucTfjxr Kf014py2aoRJHuvy85ee/zIyLmve5hngZTTe3Wg3TInT9UTFzTPhItam6dZ1xqdTGHZYGU0O otRHcwLGt470grdiob6PfVTXoHlBvkWRadMhSuG4RORCDpq89vu5QralFNIf3EysNohoFy2A LYg2/D53xbU/aa4DDzBb5b1Rkg/udO1gZocVQWrDh6I2K3+cCs7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 15.08.25 17:20, Vernon Yang wrote: > On Thu, Aug 14, 2025 at 01:58:34PM +0200, David Hildenbrand wrote: >> On 14.08.25 13:38, Vernon Yang wrote: >>> Currently pagefaults on anonymous pages support mthp, and hardware >>> features (such as arm64 contpte) can be used to store multiple ptes in >>> one TLB entry, reducing the probability of TLB misses. However, when the >>> process is forked and the cow is triggered again, the above optimization >>> effect is lost, and only 4KB is requested once at a time. >>> >>> Therefore, make pagefault write-protect copy support mthp to maintain the >>> optimization effect of TLB and improve the efficiency of cow pagefault. >>> >>> vm-scalability usemem shows a great improvement, >>> test using: usemem -n 32 --prealloc --prefault 249062617 >>> (result unit is KB/s, bigger is better) >>> >>> | size | w/o patch | w/ patch | delta | >>> |-------------|-----------|-----------|---------| >>> | baseline 4K | 723041.63 | 717643.21 | -0.75% | >>> | mthp 16K | 732871.14 | 799513.18 | +9.09% | >>> | mthp 32K | 746060.91 | 836261.83 | +12.09% | >>> | mthp 64K | 747333.18 | 855570.43 | +14.48% | >> >> You're missing two of the most important metrics: COW latency and memory >> waste. > > OK, I will add the above two test later. > >> >> Just imagine what happens if you have PMD-sized THP. >> >> I would suggest you explore why Redis used to recommend to disable THPs >> (hint: tail latency due to COW of way-too-large chunks before we do what we >> do today). > > Thanks for the suggestion, I'm not very familiar with Redis indeed. Currently, > this series supports small granularity sizes, such as 16KB, and I will also > test redis-benchmark later to see the severity of tail latency. > >> >> So staring at usemem micro-benchmark results is a bit misleading. >> >> As discussed in the past, I would actually suggest to >> >> a) Let khugepaged deal with fixing this up later, keeping CoW path >> simpler and faster. >> b) If we really really have to do this during fault time, limit it to >> some order (might even be have to be configurable). > > This is a good way to add a similar shmem_enabled knob after if need. > >> >> I really think we should keep CoW latency low and instead let khugepaged fix >> that up later. (Nico is working on mTHP collapse support) >> >> [are you handling having a mixture of PageAnonExclusive within a folio >> properly? Only staring at R/O PTEs is usually insufficient to determine >> whether you can COW or whether you must reuse]. > > There is no extra processing on PageAnonExclusive here, only judging by R/O PTEs, > thank you for pointing it out, and I will look into how to properly handle > this situation later. Yes, but as I said: I much prefer to let khugepaged handle that. I am not convinced the complexity here is warranted. Nico's patches should soon be in shape to collapse mthp. (see the list) -- Cheers David / dhildenb