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 3E9F4221DB3; Fri, 8 May 2026 20:14:01 +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=1778271241; cv=none; b=kkYPtTDum72NQ8XvKCc626jd71xwbk4kS9TnjZAMtBaJyA5ozdOtAx9L937LKCLd/are55JePb47XNB7iAOWNuXHYXLfUnvJkEbR8I0WSQBL4N+nqZRRoWWQV+cb5tR+hBz1pCkw006zDGucLmT912ty5EOMRLO4AGjHg1lJOkk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778271241; c=relaxed/simple; bh=hxYgkYjG67gsdnfV7iJptPK6UKCqEsrTTyrjyXlkR1c=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=eyWEOF1/sgj06Z6Uxx2oJ1KR2D8Gcw0m77QBdT9cGC5DtHXpxQ+NOyjEqNhGGmAJ3PF5oKipGAi+fzR60TjTEf/2460XdwZWShdLbB/ciLNRDxFC26NgsbqtAemKgvLkntnzbINP1Wzwc9d9hxBY5NhpHwzE9SEvZ5/06J7lWpU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=LHtvnfbU; 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="LHtvnfbU" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2C735C2BCB0; Fri, 8 May 2026 20:13:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1778271241; bh=hxYgkYjG67gsdnfV7iJptPK6UKCqEsrTTyrjyXlkR1c=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=LHtvnfbUnAn1itMO5JnsxJvmwUVGU8cIc09e/GNdS5u0N99UZQaOCu1FUn5eHyLFz kiU1yWY7UdIgcbhFWm7ChdnCjgQoBWHtva/iyb0ZXmrpL7koLNRthngO4y0yswIGhO gBpNjkIkRCIu4C4olmSvuEFzfuQOYLoXP/evhxI5czz1aKF/LlwtwFCqwQwVLe2HP1 WrQ6sctqlZh29QqtfiYzSuvlvwmjcnEMCegSO4qlxxZlKGVV4pmFzhRgPr2wAvgADU V/0MOSyp24Uwypku5XAbLe7Gcbntnvmp6eV6HY7xVvKUyKnOp8mtXHsJdL/tnjixjT M3ekFqMx+v39A== Message-ID: Date: Fri, 8 May 2026 22:13:50 +0200 Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 13/14] mm/khugepaged: enable clean pagecache folio collapse for writable files To: Zi Yan , Andrew Morton , "Matthew Wilcox (Oracle)" , Song Liu Cc: Chris Mason , David Sterba , Alexander Viro , Christian Brauner , Jan Kara , Lorenzo Stoakes , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Shuah Khan , linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org References: <20260429152924.727124-1-ziy@nvidia.com> <20260429153538.727855-9-ziy@nvidia.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: <20260429153538.727855-9-ziy@nvidia.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 4/29/26 17:35, Zi Yan wrote: > collapse_file() is capable of collapsing pagecache folios from writable > files to PMD folios. Now enable clean pagecache folio collapse in addition > to read-only pagecache folio collapse by removing the > inode_is_open_for_write() from file_thp_enabled() and only performing > filemap_flush() if the file is read-only. > > This means userspace needs to explicitly flush the content of pagecache > folios before khugepaged can collapse the folios, or use > madvise(MADV_COLLAPSE), which does the flush in the retry. The reason is > that blindly enabling dirty pagecache folio from writable files collapse > makes khugepaged flush these folios all the time. It is undesirable to > cause system level pagecache flushes. > > To properly support dirty pagecache folio collapse, filemap_flush() needs > to be avoided. Potentially, merging associated buffer instead of dropping > it with filemap_release_folio() might be needed. > > NOTE: this breaks khugepaged selftests for writable file pagecache > collapse, which is set to fail all the time. The next commit fix it. > > Signed-off-by: Zi Yan > --- > mm/huge_memory.c | 2 +- > mm/khugepaged.c | 9 ++++++++- > 2 files changed, 9 insertions(+), 2 deletions(-) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 9b3abb98a7e51..e1e9d59db6e70 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -97,7 +97,7 @@ static inline bool file_thp_enabled(struct vm_area_struct *vma) > if (!mapping_pmd_folio_support(vma->vm_file->f_mapping)) > return false; > > - return !inode_is_open_for_write(inode) && S_ISREG(inode->i_mode); > + return S_ISREG(inode->i_mode); > } > > /* If returns true, we are unable to access the VMA's folios. */ > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index 1ee15b48962a3..fb7ff643973cc 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -2345,7 +2345,14 @@ static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr, > * forcing writeback in loop. > */ > xas_unlock_irq(&xas); > - filemap_flush(mapping); > + /* > + * Only flush for read-only files. Writable > + * files can have their folios dirty at any > + * time; blindly flushing them would cause > + * undesirable system-wide writeback. > + */ That comment should really be merged in the comment above. Also, there we say "khugepaged only works on read-only fd" ... which is now just wrong? Please revise that whole comment as you incorporate your comment. Apart from that I guess this is fine ... or we'll learn rather quickly, haha. -- Cheers, David