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]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 344D9CCD183 for ; Mon, 13 Oct 2025 10:18:54 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 78FDA8E002E; Mon, 13 Oct 2025 06:18:53 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 73FEF8E0007; Mon, 13 Oct 2025 06:18:53 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 5E1468E002E; Mon, 13 Oct 2025 06:18:53 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id 4045D8E0007 for ; Mon, 13 Oct 2025 06:18:53 -0400 (EDT) Received: from smtpin14.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id DB368C0353 for ; Mon, 13 Oct 2025 10:18:52 +0000 (UTC) X-FDA: 83992692504.14.84684FA Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by imf03.hostedemail.com (Postfix) with ESMTP id 6257B2000D for ; Mon, 13 Oct 2025 10:18:50 +0000 (UTC) Authentication-Results: imf03.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=O05EoaX5; dmarc=pass (policy=quarantine) header.from=redhat.com; spf=pass (imf03.hostedemail.com: domain of david@redhat.com designates 170.10.133.124 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=1760350730; 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=8zLr9HRWBU4vFy2Jm9nw9zsWcFfSLePV2+VE2LgCs2c=; b=B3Qf7kdQw20xo1r5f8RihinTKQ9vNesITHO8MgMzalE4LvD18Pnf79itGyzkBx9lo2GOEv g5yqzBlfBBGuJDEAAvDIeiQf9jBuRyHKBUf+1yWPNAVPu/IKIHy89xcLx4V5fCgHJvyx+2 zouo85nWbIH4tQmOM5cfa48WVh25q1w= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1760350730; a=rsa-sha256; cv=none; b=YKkaxkpj52K6ALhwfMqu45s/swoBuO4E1BIq3deCHniNL/tu3pq8pQclmUK7oc5rZsH6pH 5tLnon8YQZn7l21ysL20mPScSpVMUcsl5H1w7E2woINmTlHp9Qgh0fg62z5ak8ByVXT7+7 V2yMjFrbtJ5yW1Dhs7hlVR+fztNfHwo= ARC-Authentication-Results: i=1; imf03.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=O05EoaX5; dmarc=pass (policy=quarantine) header.from=redhat.com; spf=pass (imf03.hostedemail.com: domain of david@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=david@redhat.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1760350729; 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=8zLr9HRWBU4vFy2Jm9nw9zsWcFfSLePV2+VE2LgCs2c=; b=O05EoaX5IKInejqK+tIRbG6C3eIGXqowBmbd6/Qbp7M7eLSMVByJekLCt78W3q2dA27Weh KThnXujXlM2UUT/vLb0Untecf7LocKw6mhavkxy1kepMk/pAS/3lnpYDggWpDH0Uuvt+B1 dE4lSHjIzQKcMzZu5KGSCTPpumXK4wI= Received: from mail-wr1-f69.google.com (mail-wr1-f69.google.com [209.85.221.69]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-494-1BzA5KoqPgWe9DdadqP7tQ-1; Mon, 13 Oct 2025 06:18:48 -0400 X-MC-Unique: 1BzA5KoqPgWe9DdadqP7tQ-1 X-Mimecast-MFC-AGG-ID: 1BzA5KoqPgWe9DdadqP7tQ_1760350727 Received: by mail-wr1-f69.google.com with SMTP id ffacd0b85a97d-3fba0d9eb87so2633885f8f.0 for ; Mon, 13 Oct 2025 03:18:48 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1760350727; x=1760955527; h=content-transfer-encoding:in-reply-to:autocrypt:content-language :references:cc:to:from:subject:user-agent:mime-version:date :message-id:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=8zLr9HRWBU4vFy2Jm9nw9zsWcFfSLePV2+VE2LgCs2c=; b=NkbV+4CKAw391toiNvwXe5fN9OSUQvlJuZFVv54Mx5lCcjlJtWlsiRDgIiBucncvnQ QDgKHA73jNMxXvVZyCGxSJICDlFWvbfjN2fk2RqgudZLpiUh8o9hYpWRUVgUlNi9L2pA 0U246VhYbFRtOYrnykYrEU2BFMAPWNwLPyQHjvKBJttK+77SiDYMEDIg6d50Rk/SOzVU kl4WElrZbOApu9YpltQ1PVRIen5pVu4ZpkL+9ovjvFBtjB2+1u5UOqm963qFopRpCYFZ cZpEsFd0QYq+1k2hmwn0sJTOHBdsXGZ16Om+w2UzWRpm78Yr8lhKoxDYJRoweV4FRMnF u/lg== X-Gm-Message-State: AOJu0YwCBjOQtXDyH0LQuiFCZXTUHvZJylrynp6r47x6lLrgMUCAa6/e dYjZe7XuZaCSZDUwelMXL2aL45XTvhzBE8Ady1I1j/7oNG7WYHx/RbBXjUVsxwW/a7jNyz8YJzZ 1rOXf6oZio51udM2FLLrH1yV2Nu4YtSqBKpNka6zbl7tzB1kLrTa9 X-Gm-Gg: ASbGnctpGkB42HgPL1vbl4d7IQ6lVbfEtGYNVihu6jEk4j9P25aby/fsD4kRuTYogip s+piMraesaO5MFuSvoDvvHJ8I+xuXWEJV6UEefrpMCWkNvt6PP4bdjlqaIXEL2EnV81Fw17xJYe GwsDNnzkBb3Zp3iB3y+ZOC6iMds1cnqSCJc4AqQO+aMEcp0NNsI176U7WUdOum4rxHovyCxwkHb UpW53DXLuQCMu3NasYSMdag5YwNCxjFqhH5K9eCXcRu0oOblRt+bROhr4KqBW8TGNcC6B4NRzuH 0CNaqSh/0a9CPGmdyZpX8GTJWndKnerGYuyFWsoJBFiELMsWVWF0lvpgMHemt3FZRa/a/l2Y3d+ f3p8= X-Received: by 2002:a05:6000:2485:b0:3ea:63d:44ca with SMTP id ffacd0b85a97d-4266e7d458bmr12984598f8f.32.1760350727198; Mon, 13 Oct 2025 03:18:47 -0700 (PDT) X-Google-Smtp-Source: AGHT+IEM/T8CkEhXD5AffHwvYXnzkgYfTcIzt0LzKyvioPOCxT53MwhT1l9CdJPTaNnAknU5ZLI2Iw== X-Received: by 2002:a05:6000:2485:b0:3ea:63d:44ca with SMTP id ffacd0b85a97d-4266e7d458bmr12984579f8f.32.1760350726810; Mon, 13 Oct 2025 03:18:46 -0700 (PDT) Received: from [192.168.3.141] (tmo-083-189.customers.d1-online.com. [80.187.83.189]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-426ce57d3b9sm17741952f8f.11.2025.10.13.03.18.44 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 13 Oct 2025 03:18:46 -0700 (PDT) Message-ID: <423de7a3-1c62-4e72-8e79-19a6413e420c@redhat.com> Date: Mon, 13 Oct 2025 12:18:44 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [Regerssion] [KSM] KSM CPU overhead in 6.16+ kernel compared to <=6.15 versions ("folio_walk_start" kernel object overhead) From: David Hildenbrand To: craftfever@murena.io, akpm@linux-foundation.org, xu.xin16@zte.com.cn, chengming.zhou@linux.dev Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, regressions@lists.linux.dev References: <020cf8de6e773bb78ba7614ef250129f11a63781@murena.io> <8e458538-69dc-4c0f-a25b-0c85ce1e866e@redhat.com> 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: <8e458538-69dc-4c0f-a25b-0c85ce1e866e@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: VcyB5CTIy58Y23JcYekuf4yjMZdenGfex1OAZGGVk1Y_1760350727 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: rspam01 X-Stat-Signature: bcirgrg637b7zbsn6ex5gqtp8rxzge7r X-Rspam-User: X-Rspamd-Queue-Id: 6257B2000D X-HE-Tag: 1760350730-344610 X-HE-Meta: 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 vbz6x9GT 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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 13.10.25 11:52, David Hildenbrand wrote: > On 13.10.25 11:22, craftfever@murena.io wrote: > > Hi, > >> I've posted about that problem already on bigzilla (#220599), but maintainers asked to post issues on maillist. >> The problem with freezes during KSM page scanning with certain processes like Chromium with huge virtual memory size amount was fized in 6.17.1 compared to 6.16.x/6.17, but problem with huge CPU overhead is present there. Compared to Linux <=6.15, where the overhead is much lighter anad there no much CPU consuming during KSM scanning, there is "folio_walk_start" kernel object is present (which I reviewed with "perf top" command) that is not present in versions <=6.15 during KSM work and which is in work starting from Linux 6.16. This method very resource-consuming compared to algorithm used in <=6.15 versions. Is there a kernel parameter to disable it or it needs more optimization? > > I doubt hat it has a lot to do with folio_walk_start(), that's just a > simple page table walk replacing the previous walk based on follow_page(). > > So that's why you would suddenly spot it in perf top -- before commit > b1d3e9bbccb4 ("mm/ksm: convert scan_get_next_rmap_item() from > follow_page() to folio_walk") we would have used follow_page(). > > Do you see any kernel splats / soft-lockups? > > I can see that in commit b1d3e9bbccb4 I removed a cond_resched(). maybe > that's why it's a problem in you kernel config. Looking again, no, that's not the case. We do a cond_resched() after every page we looked up. Also, b1d3e9bbccb4 was introduced in v6.12 already. Regarding folio_walk_start(), also nothing major changed ever since v6.12. Looking at scan_get_next_rmap_item(). I guess we might hold the mmap lock for quite a long time (if we're iterating large areas where there are no suitable pages mapped -- very large sparse areas). That would explain why we end up calling folio_walk_start() that frequently. But nothing really changed in that regard lately in KSM code. What we probably should be doing, is give up the mmap lock after scanning a certain size. Or better, switch to per-VMA locks if possible. Also, looking up each address is highly inefficient if we end up having large empty areas. A range-walk function would be much better suited for that, so we can just jump over holes completely. But anyhow, nothing seems to have changed ever since 6.15 AFAIKT, so I'm not really sure what's going on here. Likely it's unrelated to KSM changes. -- Cheers David / dhildenb