From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 E64A91F12E0 for ; Thu, 12 Feb 2026 09:10:56 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770887457; cv=none; b=kgshtwcabOgl8KDRIKdGEh2BxYyYi2f84UdVastDWzuzLnVvq7cjrrN86dw/CAVS//yHs4jlgGlbuxIUVoEqmc0bnGak31YXsJ/NSKR5j6v4lBvLdl0g0amfHmRzbFsXqdUrRNDXO5FEm3ojGqKFFTs9aZfwBdFGAR92JHM6JkE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770887457; c=relaxed/simple; bh=xQs/VONCVmMMX9dMzZmQ6NsgfiBgg83y6eg69h6scJM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=uR6qFjNoFlliw84clJYy0v0A2ze9935nW0elGl2eozMJgMp2VpnrtwmwJ+8knnW14jiT4u7e58yr0w2Id5WClWuYEfK1hMHkbNa172syceqDDS6+XV/1D3PqRldT0BQ9e7HjBVfZbBvDrgPkKs/4v0lhIjHAfyO/XrjAmqsRmRw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=c2Fwrg2W; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="c2Fwrg2W" 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 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: [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 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