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 E8D94C3DA4A for ; Mon, 5 Aug 2024 11:56:18 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 361516B0082; Mon, 5 Aug 2024 07:56:18 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 2EA7F6B0085; Mon, 5 Aug 2024 07:56:18 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 163786B0089; Mon, 5 Aug 2024 07:56:18 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id E62456B0082 for ; Mon, 5 Aug 2024 07:56:17 -0400 (EDT) Received: from smtpin09.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay04.hostedemail.com (Postfix) with ESMTP id 7BB7F1A0269 for ; Mon, 5 Aug 2024 11:56:17 +0000 (UTC) X-FDA: 82418038794.09.05D984C Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by imf16.hostedemail.com (Postfix) with ESMTP id 265A0180005 for ; Mon, 5 Aug 2024 11:56:14 +0000 (UTC) Authentication-Results: imf16.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=efAPAlIl; dmarc=pass (policy=none) header.from=redhat.com; spf=pass (imf16.hostedemail.com: domain of david@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=david@redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1722858925; a=rsa-sha256; cv=none; b=HpraQhSUYJ5yUwld03D8dOkg22yPa8G+lNx41+wy0rrvHYfPDAW4AyEsh8jXkM2Wxn/WpL sVMxBxmIYVIZgjsdH+Pk68mlomknWgMBf/iKocdFCeuVb3JK77eC7Y/gJ7KlTid1o3EtFK PjaSzGu0gaYYwUcu25jizqLaVgO3gK4= ARC-Authentication-Results: i=1; imf16.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=efAPAlIl; dmarc=pass (policy=none) header.from=redhat.com; spf=pass (imf16.hostedemail.com: domain of david@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=david@redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1722858925; 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=OdLnrLDO2Co5gynkvuqQOFnDuNj00mFAOttSvfb4hLQ=; b=2L3lfJfllYpM31qSofAazy/1RaKD4cKooPSvoftrCk2oKT9skQBfEZvfjDBI+zs/rPQ8aQ aBEHRxo0eHalTwlsmgYZbnSR64gV+0+sJ3Q6v6srWio8YtuF97ZsI1TAy4ihQiKmsGt2rs Emm9wm3+VBr8qUQPzik8/wseNF8yuCg= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1722858974; 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=OdLnrLDO2Co5gynkvuqQOFnDuNj00mFAOttSvfb4hLQ=; b=efAPAlIlFNY0v7KZkEbKzeXGv4k7l18iJtaEEGsKfzOLHynOGg/JqcECSwY8rhjamksHf4 OMRmzcaBYASBMpjEtXvCVoxjVAFBIKt/KzbuhVhNeeo1PAQ9m+nJooH5b5Q1MQyqafBy+Q 68XsXFtLg2o7RkcBQvqc/qnOpTYouD8= Received: from mail-lj1-f200.google.com (mail-lj1-f200.google.com [209.85.208.200]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-201-Ca9xzIXdNaeCE-TePUfl2g-1; Mon, 05 Aug 2024 07:56:13 -0400 X-MC-Unique: Ca9xzIXdNaeCE-TePUfl2g-1 Received: by mail-lj1-f200.google.com with SMTP id 38308e7fff4ca-2ef1b9a466cso105068691fa.3 for ; Mon, 05 Aug 2024 04:56:12 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1722858971; x=1723463771; 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=OdLnrLDO2Co5gynkvuqQOFnDuNj00mFAOttSvfb4hLQ=; b=whyJZiPyJtz4SegdnABXiluP6a03Q/H4yh1UZKjqLFNwnvD5tPx0YiwAEc0HZLUl/a DcXpg3zImjkPiOd60y7XoSb1vl8QnvMkh6r4DpC5FOySBHGHmwYqeuk68cmdjIMdfaEb xLLYsnIRrXQNNRBlgILuufFPlPAOq1QQCIDj+X0A8CRorKmmoJI1uVXndEonSqNBS6pQ NU3EtALi7kOz86m5wRHS3Za3xXvt9iZkc8B+uwI3qR63yjoD3xtAxYY5pRgWB9zlzYe3 jbIElZcNELsLh8EaQDRGHa/atAgROFvdnW7CHsMiUQXdcJb1YfHQ7Gl+u3z1VD/B3dKd VQtg== X-Forwarded-Encrypted: i=1; AJvYcCU6/c/RQkw9iGaM3nPzLrDpwg87RyZF73WeKnd7MskThw6JxfT5jPh7QZ+wz2NKnGyE9ychjoMLXeBG1JiT079lvgA= X-Gm-Message-State: AOJu0YwlzR1TixNsm+pZsucdwQ3vpOXJWEvn2mo8RlnIm5ocWqmGj7eo TYe4GG3Eg1LPI/lHN2eu3L1IU7aUCN4X1UCGIXHPTp+MYJLARQ+lJ+yw8x4ocYIDKdVYAxRWmnp xvkfmg/C7GJ+R5+pu8YSNM3TqsTJV3TXW1j0KuLHzTKRRQ+u/ X-Received: by 2002:a2e:7d12:0:b0:2ef:216c:c97 with SMTP id 38308e7fff4ca-2f15aaacbb7mr79872351fa.19.1722858971424; Mon, 05 Aug 2024 04:56:11 -0700 (PDT) X-Google-Smtp-Source: AGHT+IHLbnJQ1TLJnqLPIOmTqzQFwSa7LCs6N4frJ3HQQaVHS//v/xdiuZcBEkkW/nbu8vPwC5ZNBg== X-Received: by 2002:a2e:7d12:0:b0:2ef:216c:c97 with SMTP id 38308e7fff4ca-2f15aaacbb7mr79872161fa.19.1722858970824; Mon, 05 Aug 2024 04:56:10 -0700 (PDT) Received: from ?IPV6:2a09:80c0:192:0:5dac:bf3d:c41:c3e7? ([2a09:80c0:192:0:5dac:bf3d:c41:c3e7]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-36bbcf0dc9asm9557502f8f.15.2024.08.05.04.56.10 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 05 Aug 2024 04:56:10 -0700 (PDT) Message-ID: <6b5f1ea1-4ebe-41c7-9a0f-0cf3418af815@redhat.com> Date: Mon, 5 Aug 2024 13:56:09 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] Hitshield : Something new eviction process for MGLRU To: Minwoo Jo , akpm@linux-foundation.org Cc: rostedt@goodmis.org, mhiramat@kernel.org, willy@infradead.org, linux-mm@kvack.org References: <20240802000546.322036-1-chminoo@g.cbnu.ac.kr> 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: <20240802000546.322036-1-chminoo@g.cbnu.ac.kr> 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: 7bit X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 265A0180005 X-Stat-Signature: j57xf9gbuqtqse6kj77fqwntnnaw8fww X-Rspam-User: X-HE-Tag: 1722858974-998153 X-HE-Meta: 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 FH2ZQgoN 2Xo5h6XMpNae70I/pDXqQBPPwe3IYiY2Uc4C2eb0Pi1QCgjIKVf/nY+o954Yj6mUJhQjFuWaviiQYZejWNiuVUQx+cfVYwKljOGpRVXklMxeuM91b5gdraMRJruU05cQOTtnmuINbMfAJJv7q0c1plcVQbPaOOnpIrY6OBsbeYpf9saZhDF9ydgVtYpXDaKGQzZaqv9MbXifbjrlF2shAer7lstKlzlKP/+uwGLacige9FkZiV1hTO7WA18/y7+bF0Rv+JjRAGohn2kadEaEU/fG1w7kJ9rNecAm4grIxKzrGuMcwvU8XZ2vPRbN+fs3C9IDYoKaoCzBaUoT2kWqY2TJQU5xAjnoXQu3zFOJ/J64uNTyaBiljB68IvYFsywDpA/Ey/FvMAhMaZOLuXepALRuFEodvpoIUPU1wIN2BoVboHUU= 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 02.08.24 02:05, Minwoo Jo wrote: > Signed-off-by: Minwoo Jo > > This commit addresses the page space occupancy issue that arose > in the previous commit with the HitShield technology. > > The HitShield technology is based on the observation that MGLRU > does not take into account the state of the folio during eviction. > > I assumed that if a folio, which has been updated only 1 to 3 times, > has increased in generation until the point of eviction, > it is likely to be referenced less in the future. > > Therefore, I implemented this technology to protect frequently updated folios. > > I added the hitshield_0, hitshield_1, and hitshield flags to the page flag. > > Upon my review, I confirmed that the flags occupy positions 0 to 28. > > Thus, I believe that allocating 3 flags, or 3 bits, is sufficient. > > The hitshield_0 and hitshield_1 flags serve as count flags, representing the digit positions in binary. > > The hitshield flag is a boolean flag used to verify whether the HitShield is actually enabled. > > Each time a folio is added to lrugen, the hitshield_0 and hitshield_1 flags are cleared to reset them. > > Subsequently, in the folio_update_gen function, I added the following code: > > if (!folio_test_hitshield(folio)) > if (folio_test_change_hitshield_0(folio)) > if (folio_test_change_hitshield_1(folio)) > folio_set_hitshield(folio); > > This code counts the HitShield, and if it exceeds 5, it sets the hitshield flag. > > In the sort_folio function, which is executed for eviction, if the folio's hitshield flag is set, > it ages the folio to max_gen and resets the flag. > > The testing was conducted on Ubuntu 24.04 LTS (Kernel 6.8.0) > with an AMD Ryzen 9 5950X 16Core (32Threads) environment, restricting DRAM to 750MiB through Docker. > > In this environment, the ycsb benchmark was tested using the following command: > > ./bin/ycsb load mongodb -s -P workloads/workloadf -p recordcount=100000000 -p mongodb.batchsize=1024 > -threads 32 -p mongodb.url="mongodb://localhost:27017/ycsb" > > During testing, a reduction of 78.9% in pswpin and 75.6% in pswpout was measured. > > Additionally, the runtime for the Load command decreased by 18.3%, > and the runtime for the Run command decreased by 9.3%. > > However, when running a single-threaded program with the current implementation, > while a decrease in swap counts was observed, the runtime increased compared to the native MGLRU. > > A thorough analysis is needed to understand why this occurs, but I think it appears > that there is significant overhead from the flag calculations. > > Therefore, it seems that if we activate this functionality through an ifdef statement > only in certain situations, we could achieve performance benefits. > > As an undergraduate student who is still self-studying the kernel, I am not very familiar with using ifdef, > so I did not write that part separately. > > I apologize for not being able to test it with large memory swap workloads, > as I was unsure what would be appropriate. > > I would appreciate your review and feedback on this approach. > > Thank you. > --- > include/linux/mm_inline.h | 4 ++++ > include/linux/page-flags.h | 26 ++++++++++++++++++++++++++ > include/trace/events/mmflags.h | 5 ++++- > mm/vmscan.c | 22 ++++++++++++++++++++++ > 4 files changed, 56 insertions(+), 1 deletion(-) > > diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h > index f4fe593c1400..dea613b2785c 100644 > --- a/include/linux/mm_inline.h > +++ b/include/linux/mm_inline.h > @@ -266,6 +266,10 @@ static inline bool lru_gen_add_folio(struct lruvec *lruvec, struct folio *folio, > else > list_add(&folio->lru, &lrugen->folios[gen][type][zone]); > > + folio_clear_hitshield_0(folio); > + folio_clear_hitshield_1(folio); > + /* This for initialize hit_shield by 0 when folio add to gen */ > + > return true; > } > > diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h > index 5769fe6e4950..70951c6fe4ce 100644 > --- a/include/linux/page-flags.h > +++ b/include/linux/page-flags.h > @@ -130,6 +130,16 @@ enum pageflags { > PG_arch_2, > PG_arch_3, > #endif > + PG_hitshield_0, > + PG_hitshield_1, > + PG_hitshield, > + > + /* > + * The flags consist of two types: one for counting the update occurrences > + * of the folio and another boolean flag to check whether the HitShield is activated. > + */ Note that adding new pageflags is frowned upon -- we're actually trying to get rid of some of them, like PG_error. Getting another 3 added seems very .. unlikely :) Especially when done unconditionally on 32bit as well this might just not work at all, and as you state, would require #ifdefery. -- Cheers, David / dhildenb