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 6CA8E17736 for ; Fri, 6 Feb 2026 08:36:25 +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=1770366985; cv=none; b=SohumNKWkV6YP03JbZeeNz6j0ZW6VvERYdbwnm+JdheVbQgINo2TtHO7+orG3qSlJ8zf/H2Vk8+yFL77XglbHH+6KZN4FpX/qxsHD+6tFXsxDywKCns5rbSnRTE+VoA6KaIZd45ktdCd4V22N5+ngu54JloaQdZA4XGdL3MZV8Y= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770366985; c=relaxed/simple; bh=60sXKh54dFupXDZ+oEQgwWCw9zthbOhUf3zVTKyrWO8=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=r1n5SmFiz3uM/JfMzuC1RQtiuNdFi12S4c+lKrMnroHqWN8BR+OyRE7/zSYtRHr5Df5O1hvtaPtbkxpEm1g6QgL00MaCjF+Ua55aVXajXdBEu5jvKU6mPh2G161mbvFj8Cgzqm72ZH+ukmSGrcKM+3WCrv4O2ifCdYIaP/RPu4E= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=WnqjjJUM; 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="WnqjjJUM" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 137CCC116C6; Fri, 6 Feb 2026 08:36:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1770366985; bh=60sXKh54dFupXDZ+oEQgwWCw9zthbOhUf3zVTKyrWO8=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=WnqjjJUMboX0/6BWcCU+SJRLWP+GnBUjR3aYVurgfcD1iS3vVElyv8sX1+UKd0Sdl AYOvMsj9roCddWSwCjtAifSnhTKIMx2aY9NYtFqmZvdR5x7/NsOi2XF9oyE6Rw0RiG 7cey/09Tt++9fPja52NXTF4WzHwdZXauIITpyRGAglW8TPYNw04ND4FX98w/GU3ziM 66OfJnZ8XWMWsrsh1qld17kpwRb1xGcgrIjzav9vL6fEKG7PRwCD2fgFNGaW2oP4yL 6BMAnumxMtRSvv/HOmwUxuIm9rPY0PtXNaow+oscOGEBYcSMuMfL8uW3kS/Hc2RYwc REqoRnGvtRNiA== Message-ID: Date: Fri, 6 Feb 2026 09:36:20 +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: [stable-6.6.y] mm: khugepaged refuses to freeze To: Baolin Wang , Sergey Senozhatsky Cc: Andrew Morton , Lorenzo Stoakes , Zi Yan , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <3d0f189b-faab-4452-b9cc-8f4e7a15025f@linux.alibaba.com> <1179320d-6bab-40a4-a7ac-dbcfbab24623@linux.alibaba.com> 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: <1179320d-6bab-40a4-a7ac-dbcfbab24623@linux.alibaba.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 2/6/26 06:12, Baolin Wang wrote: > > > On 2/6/26 12:31 PM, Sergey Senozhatsky wrote: >> On (26/02/06 12:38), Sergey Senozhatsky wrote: >> [..] >>> >>> Right, I thought about it but wasn't sure.  Could the inner loop (e.g. >>> collapse_file() in this particular case) loop long enough to fail >>> suspend >>> w/o ever giving the outer loop (khugepaged_do_scan()) a chance to >>> freeze? > > Yes, that’s possible. However, if we add a try_to_freeze() check in the > inner loop, we need to consider various scenarios (such as anonymous > folio swap-in and other potential cases?), which feels too hacky to me. > >> For inner loops I wondered if cond_resched() could be an indicator of >> where try_to_freeze() should be placed.  Those cond_resched() calls >> are there for a reason, after all.   E.g. something like: >> >> --- >> >> diff --git a/mm/khugepaged.c b/mm/khugepaged.c >> index fa6a018b20a8..cee08466a069 100644 >> --- a/mm/khugepaged.c >> +++ b/mm/khugepaged.c >> @@ -2431,6 +2431,9 @@ static unsigned int >> khugepaged_scan_mm_slot(unsigned int pages, enum scan_result >>           unsigned long hstart, hend; >>           cond_resched(); >> +        if (try_to_freeze()) >> +            break; >> + >>           if (unlikely(hpage_collapse_test_exit_or_disable(mm))) { >>               progress++; >>               break; >> @@ -2453,6 +2456,9 @@ static unsigned int >> khugepaged_scan_mm_slot(unsigned int pages, enum scan_result >>               bool mmap_locked = true; >>               cond_resched(); >> +            if (try_to_freeze()) >> +                goto breakouterloop; >> + >>               if (unlikely(hpage_collapse_test_exit_or_disable(mm))) >>                   goto breakouterloop; > > This looks better than the previous version. Let’s also wait to see if > others have any better suggestions. What prevents other callpaths (faults, read(), write(), etc) from similarly triggering swapin? I recall that there is a notifier when the system is preparing to sleep (pm notifier or something). Could we simply hook into that to tell khugepaged to suspend+resume? Essentially, making hpage_collapse_test_exit_or_disable() break our for us. -- Cheers, David