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 BF9E9EB48EC for ; Thu, 12 Feb 2026 09:11:00 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 0C50B6B008A; Thu, 12 Feb 2026 04:11:00 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 072A96B008C; Thu, 12 Feb 2026 04:11:00 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id E6C126B0092; Thu, 12 Feb 2026 04:10:59 -0500 (EST) 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 D07566B008A for ; Thu, 12 Feb 2026 04:10:59 -0500 (EST) Received: from smtpin29.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay03.hostedemail.com (Postfix) with ESMTP id 7FC42BB123 for ; Thu, 12 Feb 2026 09:10:59 +0000 (UTC) X-FDA: 84435235038.29.5537253 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf20.hostedemail.com (Postfix) with ESMTP id A7C591C0008 for ; Thu, 12 Feb 2026 09:10:57 +0000 (UTC) Authentication-Results: imf20.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=c2Fwrg2W; spf=pass (imf20.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1770887457; 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=QjQDGtFNN2J1VmXqWgnD5xSGrgTNMhKvNE6JI7bwQ+w=; b=ugRbyfx/KhQxXgn7Fr4U4i9Vl9e6ZxkWntcSVjCP/kjiQVxzm7CZj9zcuyIeRZi8KBQEGu 9Y94xFkRmQ/93Q7QIANZjnO6RRj0SGPyrJhFd4JAiEg43TKCr7YbpBGsAmNRN0KXTIOEFc qeVF1zWKyMg6uS6kHXtb5g8UMZZ1w04= ARC-Authentication-Results: i=1; imf20.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=c2Fwrg2W; spf=pass (imf20.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1770887457; a=rsa-sha256; cv=none; b=OEqdbmsDYp55Qn7B57MhSkHxOQ0O4PZkbQ9E4D66uPIbwI68dFAl7y/ZNE4dF8fq0ZikPy 8eBpF1CtMO6ZYASojIwmjOvBLty4EGWba5CTA3O4DvHA6B9Rdc+SgbeP1jYVXXzx8KNBcI ivoROZcfPnnnbjxdkiSlb2bU0L7YYi0= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id B771C43B4E; Thu, 12 Feb 2026 09:10:56 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id B2FF4C4CEF7; Thu, 12 Feb 2026 09:10:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1770887456; bh=xQs/VONCVmMMX9dMzZmQ6NsgfiBgg83y6eg69h6scJM=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=c2Fwrg2WKfAxdMW+LEhD9IDgnuJaxmVW+GRnftndIOq/z25H5YsYQ/ET0XPjWFFJ8 ksa/UeIe8J6b7ZyFcaXRwTZqKylxPbJqfUUFhGY4o/jJmuFTf6uOpUdsr4Zm71L2qA 9GcXlXAlDtcB2Fyanz0vomXDT1yfIRNo4p/g8wmcbC0TJ8QM2Aze/HhIDT1BexBOEq Lrvaub2W/HJI+C/kK7Q7lTzbLyULnNR4hUZgJy5JUJiZquljYX1jrbX6CtHvMOZdMI tcj841/bCxn3SBb3F5ks5XoFSWVNhqWLAzlToKw8aLxXAgVecmQmRg8lDbp9nObfjc qCe33v38obcuA== Message-ID: <16ce9ce2-8081-482c-a6ea-0932ebd081f1@kernel.org> Date: Thu, 12 Feb 2026 10:10:49 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCHv2] mm: khugepaged: make scan loops suspend aware To: Sergey Senozhatsky Cc: Andrew Morton , Lorenzo Stoakes , Zi Yan , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260211031512.261127-1-senozhatsky@chromium.org> <104bc764-5a20-4ac2-95a8-b31f41255766@kernel.org> <3571cf8b-9fb3-41b2-a402-a8537ee2c399@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+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 X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: A7C591C0008 X-Stat-Signature: n33fpy75zkbuz5ituhtrdgoxgacwtbdh X-Rspam-User: X-HE-Tag: 1770887457-919118 X-HE-Meta: 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 oe0PzWJ9 GMUpuJf89I2Lc/VIF0j4lKe6jjU8s3Yuc5WoP90gEMyGQl+eo3l/tUf6QZZ1eflmkmMhQy1Hyndk78ZQe46MyZpgNsIq+uiO6/R4fL/JwXgW8aLXjgm9pTPlK7oNyW11XBi+VE9wYoH/KO1cRalq2HguNsZdqYiE2/vF3S92TnTnBILmIOfN86rqOCaOYKIWovHkkPoRy3Pr5Utbqsy1k4wLqO3w20URzO1ZVMsIaO9Tf39pSqerdC2FItlGn+0vzzAlcAJDYeHwG9ulEtoNHSBHTHcXV/o3tlkCoGXQ8fBZSDHfsh4pcvszhGg== 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 2/12/26 10:05, Sergey Senozhatsky wrote: > On (26/02/12 09:44), David Hildenbrand (Arm) wrote: > [..] >> If we're fixing an issue, we usually try to identify which commit introduced the >> issue. >> >> For example, support for freezing was introduced in >> >> commit 878aee7d6b5504e01b9caffce080e792b6b8d090 >> Author: Andrea Arcangeli >> Date: Thu Jan 13 15:47:10 2011 -0800 >> >> thp: freeze khugepaged and ksmd >> It's unclear why schedule friendly kernel threads can't be taken away by >> the CPU through the scheduler itself. It's safer to stop them as they can >> trigger memory allocation, if kswapd also freezes itself to avoid >> generating I/O they have too. >> >> >> >> Now that I am looking through the history, I find: >> >> commit b39ca208403c8f2c17dab1fbfef1f5ecaff25e53 >> Author: Kevin Hao >> Date: Wed Dec 20 07:17:53 2023 +0800 >> >> mm/khugepaged: remove redundant try_to_freeze() >> A freezable kernel thread can enter frozen state during freezing by either >> calling try_to_freeze() or using wait_event_freezable() and its variants. >> However, there is no need to use both methods simultaneously. The >> freezable wait variants have been used in khugepaged_wait_work() and >> khugepaged_alloc_sleep(), so remove this redundant try_to_freeze(). >> I used the following stress-ng command to generate some memory load on my >> Intel Alder Lake board (24 CPUs, 32G memory). >> >> >> I wonder if that made the issue more likely to appear? >> >> >> Interestingly, we also had in the past: >> >> commit 1dfb059b9438633b0546c5431538a47f6ed99028 >> Author: Andrea Arcangeli >> Date: Thu Dec 8 14:33:57 2011 -0800 >> >> thp: reduce khugepaged freezing latency >> khugepaged can sometimes cause suspend to fail, requiring that the user >> retry the suspend operation. >> >> >> So it's a recurring theme. > > Interesting, so 1dfb059b9438633 and 878aee7d6b5504e fixed real > problems "khugepaged can sometimes cause suspend to fail", but > I don't see what exactly b39ca208403c8f2 fixed. Sounds more > like an "optimization"? Yes, a cleanup. I wonder if it caused harm. > >> Given that we only scan "khugepaged_pages_to_scan" pages/ptes/etc. before going back to sleep, >> I wonder how that can take in your setup that long. >> >> Why does it end up taking something around 20 seconds in your setup? > > I only have bug reports at hands, I don't have a repro. Can the fact > that swap reads require S/W decompression (zram) add enough latency? I guess so. 20 seconds is still a lot. > >> How is khugepaged_pages_to_scan set in your environment? > > Let me check. > > cat /sys/kernel/mm/transparent_hugepage/khugepaged/pages_to_scan > 4096 > > Hmm, doesn't sound too high. Let me look more. Yeah, that's not a lot of pages to scan. It's the default (8 * HPAGE_PMD_NR) -- Cheers, David