From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 160E7C3DA64 for ; Thu, 1 Aug 2024 16:27:32 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 880C96B0089; Thu, 1 Aug 2024 12:27:32 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 860CB6B008C; Thu, 1 Aug 2024 12:27:32 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 6D0BA6B0092; Thu, 1 Aug 2024 12:27:32 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 4FE7B6B0089 for ; Thu, 1 Aug 2024 12:27:32 -0400 (EDT) Received: from smtpin18.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay09.hostedemail.com (Postfix) with ESMTP id BF5C280925 for ; Thu, 1 Aug 2024 16:27:31 +0000 (UTC) X-FDA: 82404207102.18.2AF305C Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by imf04.hostedemail.com (Postfix) with ESMTP id 447F940011 for ; Thu, 1 Aug 2024 16:27:28 +0000 (UTC) Authentication-Results: imf04.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=bafywp8U; spf=pass (imf04.hostedemail.com: domain of david@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1722529620; a=rsa-sha256; cv=none; b=XfpGAE14SyTb+hApXqOqx3tyRlNsk1df3hKh/ge/pr0UFrW7/KYjztmUzDHL28v/Yoi2BF gG3ByLj7zg4Cph4ZIKcaAwAFUy+TFvU74ZgezprBgw4Baum5lmHcm++4o1Mpy8+Fsvp19k hAO6QOApLbAqwn8SJQRamY1xHP6kHD0= ARC-Authentication-Results: i=1; imf04.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=bafywp8U; spf=pass (imf04.hostedemail.com: domain of david@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1722529620; h=from:from:sender: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:dkim-signature; bh=sGT3n6LoTx3/d3SyMjvU1a53qjkkl05R7B/3FJ3JRRc=; b=v34a2y+U8wwTbAmfZ/Uk6CTS40t34mFH9EQnfgSRO9yC+Xt2vmUAx6nJSzdCAF9SG2bJCs CpCshoTCAixBJKnxB/6JURGgzO0b/g6saldN2EMUBtwBUsrEF6OJbJH9aMBHuAVl+GfPv6 uswJ3vIMfmSLtoa6Q5g09yLBC1t0by8= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1722529648; 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=sGT3n6LoTx3/d3SyMjvU1a53qjkkl05R7B/3FJ3JRRc=; b=bafywp8U567GDllo9IJcs5ybx+xfFYZ8PK3DfBHwYomr68Wb4FEapqoRNTlK/M0cjQYDke 2Pkr9y/K2UX0UU9A+dWEmigFUDIqZZ6+D1litzndoGjSZQZwsvt8SkmtYQ4vLHnuAWla0W 2qVvF6TtpXIJmm7X0L+hxJbcaMtVNxA= Received: from mail-wm1-f70.google.com (mail-wm1-f70.google.com [209.85.128.70]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-14-ZBNoQ9AzNQ2W7fLBAoP9RA-1; Thu, 01 Aug 2024 12:27:25 -0400 X-MC-Unique: ZBNoQ9AzNQ2W7fLBAoP9RA-1 Received: by mail-wm1-f70.google.com with SMTP id 5b1f17b1804b1-427ffa0c9c7so66849035e9.1 for ; Thu, 01 Aug 2024 09:27:24 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1722529644; x=1723134444; h=content-transfer-encoding:in-reply-to:organization: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=sGT3n6LoTx3/d3SyMjvU1a53qjkkl05R7B/3FJ3JRRc=; b=qkB2tu4wm0S1d5Ml/pzHoX21izgFmeTgZwnmd2Fl7TtZu5pWQOTGjDy0Q23AZQtqdU E6LxSlvxQh80/taQeeXDJvjAw08L7Q7bzGjuNUha0PNdCiILuaPaxCHZrCbkv5AzJh/A e/u23EDzZXhGT+0qX9y1IBVc8ce+TJbGHxr1hE6TiR3KSqY0BfMIFfb8tfJy9Oc3e4XY siKmqRssVolmAMIasen41+JmtfjXNGPj0NeawvtKc/DFsk/r90AzxM/o618AVc+vKFsT 49rX1dyoTHetTy41/dYYZd6sy+/DsDdrK4Tr7y3gmHgwAAY09Rt6d98mbitCX0fh/8OQ iyew== X-Forwarded-Encrypted: i=1; AJvYcCUDTmyrW47/x98v8CWN2RQcv2dictyHhLslMvWXe4LhZW5Tu1vMIs8A56F9dIlP3zKZHeins+fRm3qdUiwBPrfpT1o= X-Gm-Message-State: AOJu0YzGCeodaBjZuoVoJv1Vhdiv3D4qd5HAkTCGsiyuYgEkyI7ei46v hgeji68b/DkGzipm2j7jDm7pRLtgay3qcA4lfyIUqLLAi8AN1BtArH7gby9iUh0gMNCoJ5T7B2/ 2UpRzJy332cHB/lU+6ewBErjNE30qayXjDBQvxCGa4UY7W02u X-Received: by 2002:a05:600c:3d0b:b0:428:fcb:962 with SMTP id 5b1f17b1804b1-428e6b956e2mr3187325e9.36.1722529643804; Thu, 01 Aug 2024 09:27:23 -0700 (PDT) X-Google-Smtp-Source: AGHT+IHiIXJIphIdlNN8PrOJMV2NgCT5W5MzZlMG7lvlG7J9DdbrNPEccTlGOCkmG9yPPATJOxitCw== X-Received: by 2002:a05:600c:3d0b:b0:428:fcb:962 with SMTP id 5b1f17b1804b1-428e6b956e2mr3187095e9.36.1722529643242; Thu, 01 Aug 2024 09:27:23 -0700 (PDT) Received: from [192.168.3.141] (p4ff235e4.dip0.t-ipconnect.de. [79.242.53.228]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-36b36862516sm19749091f8f.104.2024.08.01.09.27.22 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 01 Aug 2024 09:27:22 -0700 (PDT) Message-ID: <524fb638-73b2-45e7-ae2c-7445d394ed50@redhat.com> Date: Thu, 1 Aug 2024 18:27:21 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 0/6] mm: split underutilized THPs To: Usama Arif , Yu Zhao Cc: akpm@linux-foundation.org, linux-mm@kvack.org, hannes@cmpxchg.org, riel@surriel.com, shakeel.butt@linux.dev, roman.gushchin@linux.dev, baohua@kernel.org, ryan.roberts@arm.com, rppt@kernel.org, willy@infradead.org, cerasuolodomenico@gmail.com, corbet@lwn.net, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, kernel-team@meta.com References: <20240730125346.1580150-1-usamaarif642@gmail.com> From: David Hildenbrand 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 ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Stat-Signature: 7oct5y5oeqzj5ba9gmi7bi5ri4phgqb9 X-Rspamd-Queue-Id: 447F940011 X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1722529648-421884 X-HE-Meta: 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 Mb/Rse2H 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 01.08.24 18:22, Usama Arif wrote: > > > On 01/08/2024 07:09, Yu Zhao wrote: >> On Tue, Jul 30, 2024 at 6:54 AM Usama Arif wrote: >>> >>> The current upstream default policy for THP is always. However, Meta >>> uses madvise in production as the current THP=always policy vastly >>> overprovisions THPs in sparsely accessed memory areas, resulting in >>> excessive memory pressure and premature OOM killing. >>> Using madvise + relying on khugepaged has certain drawbacks over >>> THP=always. Using madvise hints mean THPs aren't "transparent" and >>> require userspace changes. Waiting for khugepaged to scan memory and >>> collapse pages into THP can be slow and unpredictable in terms of performance >>> (i.e. you dont know when the collapse will happen), while production >>> environments require predictable performance. If there is enough memory >>> available, its better for both performance and predictability to have >>> a THP from fault time, i.e. THP=always rather than wait for khugepaged >>> to collapse it, and deal with sparsely populated THPs when the system is >>> running out of memory. >>> >>> This patch-series is an attempt to mitigate the issue of running out of >>> memory when THP is always enabled. During runtime whenever a THP is being >>> faulted in or collapsed by khugepaged, the THP is added to a list. >>> Whenever memory reclaim happens, the kernel runs the deferred_split >>> shrinker which goes through the list and checks if the THP was underutilized, >>> i.e. how many of the base 4K pages of the entire THP were zero-filled. >>> If this number goes above a certain threshold, the shrinker will attempt >>> to split that THP. Then at remap time, the pages that were zero-filled are >>> not remapped, hence saving memory. This method avoids the downside of >>> wasting memory in areas where THP is sparsely filled when THP is always >>> enabled, while still providing the upside THPs like reduced TLB misses without >>> having to use madvise. >>> >>> Meta production workloads that were CPU bound (>99% CPU utilzation) were >>> tested with THP shrinker. The results after 2 hours are as follows: >>> >>> | THP=madvise | THP=always | THP=always >>> | | | + shrinker series >>> | | | + max_ptes_none=409 >>> ----------------------------------------------------------------------------- >>> Performance improvement | - | +1.8% | +1.7% >>> (over THP=madvise) | | | >>> ----------------------------------------------------------------------------- >>> Memory usage | 54.6G | 58.8G (+7.7%) | 55.9G (+2.4%) >>> ----------------------------------------------------------------------------- >>> max_ptes_none=409 means that any THP that has more than 409 out of 512 >>> (80%) zero filled filled pages will be split. >>> >>> To test out the patches, the below commands without the shrinker will >>> invoke OOM killer immediately and kill stress, but will not fail with >>> the shrinker: >>> >>> echo 450 > /sys/kernel/mm/transparent_hugepage/khugepaged/max_ptes_none >>> mkdir /sys/fs/cgroup/test >>> echo $$ > /sys/fs/cgroup/test/cgroup.procs >>> echo 20M > /sys/fs/cgroup/test/memory.max >>> echo 0 > /sys/fs/cgroup/test/memory.swap.max >>> # allocate twice memory.max for each stress worker and touch 40/512 of >>> # each THP, i.e. vm-stride 50K. >>> # With the shrinker, max_ptes_none of 470 and below won't invoke OOM >>> # killer. >>> # Without the shrinker, OOM killer is invoked immediately irrespective >>> # of max_ptes_none value and kill stress. >>> stress --vm 1 --vm-bytes 40M --vm-stride 50K >>> >>> Patches 1-2 add back helper functions that were previously removed >>> to operate on page lists (needed by patch 3). >>> Patch 3 is an optimization to free zapped tail pages rather than >>> waiting for page reclaim or migration. >>> Patch 4 is a prerequisite for THP shrinker to not remap zero-filled >>> subpages when splitting THP. >>> Patches 6 adds support for THP shrinker. >>> >>> (This patch-series restarts the work on having a THP shrinker in kernel >>> originally done in >>> https://lore.kernel.org/all/cover.1667454613.git.alexlzhu@fb.com/. >>> The THP shrinker in this series is significantly different than the >>> original one, hence its labelled v1 (although the prerequisite to not >>> remap clean subpages is the same).) >>> >>> Alexander Zhu (1): >>> mm: add selftests to split_huge_page() to verify unmap/zap of zero >>> pages >>> >>> Usama Arif (3): >>> Revert "memcg: remove mem_cgroup_uncharge_list()" >>> Revert "mm: remove free_unref_page_list()" >>> mm: split underutilized THPs >>> >>> Yu Zhao (2): >>> mm: free zapped tail pages when splitting isolated thp >>> mm: don't remap unused subpages when splitting isolated thp >> >> I would recommend shatter [1] instead of splitting so that >> 1) whoever underutilized their THPs get punished for the overhead; >> 2) underutilized THPs are kept intact and can be reused by others. >> >> [1] https://lore.kernel.org/20240229183436.4110845-3-yuzhao@google.com/ > > The objective of this series is to reduce memory usage, while trying to keep the performance benefits you get of using THP=always. Punishing any applications performance is the opposite of what I am trying to do here. > For e.g. if there is only one main application running in production, and its using majority of the THPs, then reducing its performance doesn't make sense. > I'm not sure if there would really be a performance degradation regarding the THP, after all we zap PTEs either way. Shattering will take longer because real migration is involved IIUC. > Also, just going through the commit, and found the line "The advantage of shattering is that it keeps the original THP intact" a bit confusing. I am guessing the THP is freed? i.e. if a 2M THP has 10 non-zero filled base pages and the rest are zero-filled, then after shattering we will have 10*4K memory and not 2M+10*4K? Is it the case the THP is reused at next fault? The idea is (as I understand it) to free the full THP abck to the buddy, replacing the individual pieces that are kept to freshly allocated order-0 pages from the buddy. -- Cheers, David / dhildenb