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 95EE5355042; Thu, 22 Jan 2026 22:35:10 +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=1769121310; cv=none; b=skDKqm7mQPqIR0wvisrtlz2yR3nj15JzNfwDAVSpqftI0FubAU5maosnRsYh1AuTpVqtxMIu91GJT1t+jMcMO3rXF9/sYbtt6VIcFnKnwZjurMrdVUlndhe81X5NlDorj3mijYAk2q/uHrITHuEHjcDVzdGKeN8uEwPx/Dtcg+Q= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769121310; c=relaxed/simple; bh=cel+85lgP008k2TuZNt+HCFnz2aRhDRJY2Ab7DEOzEE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=LE89bNGxXaZ3YvwJgEqL7LJ2YlwpcwifHHW+ITT+n+oJIZlMHi21FZMv99wUBU7c94Iz+T5H0BPPeNwcsBLriTNR7A/rHHRIIKVF4LLpBeEwZVin6bYmchX97Sd2yeXC7TeSXg8kyD9AwoJQL+gXtbbQFjr2r3mXudN4ROOOpvU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=gMuITffC; 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="gMuITffC" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B8287C116C6; Thu, 22 Jan 2026 22:35:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1769121309; bh=cel+85lgP008k2TuZNt+HCFnz2aRhDRJY2Ab7DEOzEE=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=gMuITffCjqizZ6qdmb0Rx4n1xO3es9euuSRc+oEYJyy9llTs3jtl8Ug0qXoQNCNEV iRTY17A9NU3zNCZRIbVAJ7SQKe6HOVW1D0DaknGltAs5id0FYibzX9CBuhlmQy0T6X dLLou0mJ1DToeshTVPcBhyM4XnOeDJgW/SLRAg0vuvUyZRTENr/XnKshJmR1QZbUEP gQ9o1n94fFs+ZU73EcvuFB86gs2TrWrKFfwuneULrGy6iJxUoW85Ey3IZxpxyLhTQT /tVObpHKWi/jX94lkakYsNc8uO5+U10tikJt9NhchbWUlJDubzHooW8XAcvZUhzvva BIM18QlsSa+gg== Message-ID: Date: Thu, 22 Jan 2026 23:34:49 +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: [PATCH V5 2/2] mm/khugepaged: retry with sync writeback for MADV_COLLAPSE To: Dev Jain , Shivank Garg , Andrew Morton , Lorenzo Stoakes Cc: Zi Yan , Baolin Wang , "Liam R . Howlett" , Nico Pache , Ryan Roberts , Barry Song , Lance Yang , Masami Hiramatsu , Steven Rostedt , linux-trace-kernel@vger.kernel.org, Mathieu Desnoyers , Zach O'Keefe , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Stephen Rothwell , Branden Moore References: <20260118190939.8986-2-shivankg@amd.com> <20260118190939.8986-7-shivankg@amd.com> <3aaa3e5d-7f66-40fc-a5b0-ea6a384a88a8@arm.com> From: "David Hildenbrand (Red Hat)" 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 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAa2VybmVsLm9yZz7CwY0EEwEIADcWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCaKYhwAIbAwUJJlgIpAILCQQVCgkIAhYCAh4FAheAAAoJEE3eEPcA/4Naa5EP/3a1 9sgS9m7oiR0uenlj+C6kkIKlpWKRfGH/WvtFaHr/y06TKnWn6cMOZzJQ+8S39GOteyCCGADh 6ceBx1KPf6/AvMktnGETDTqZ0N9roR4/aEPSMt8kHu/GKR3gtPwzfosX2NgqXNmA7ErU4puf zica1DAmTvx44LOYjvBV24JQG99bZ5Bm2gTDjGXV15/X159CpS6Tc2e3KvYfnfRvezD+alhF XIym8OvvGMeo97BCHpX88pHVIfBg2g2JogR6f0PAJtHGYz6M/9YMxyUShJfo0Df1SOMAbU1Q Op0Ij4PlFCC64rovjH38ly0xfRZH37DZs6kP0jOj4QdExdaXcTILKJFIB3wWXWsqLbtJVgjR YhOrPokd6mDA3gAque7481KkpKM4JraOEELg8pF6eRb3KcAwPRekvf/nYVIbOVyT9lXD5mJn IZUY0LwZsFN0YhGhQJ8xronZy0A59faGBMuVnVb3oy2S0fO1y/r53IeUDTF1wCYF+fM5zo14 5L8mE1GsDJ7FNLj5eSDu/qdZIKqzfY0/l0SAUAAt5yYYejKuii4kfTyLDF/j4LyYZD1QzxLC MjQl36IEcmDTMznLf0/JvCHlxTYZsF0OjWWj1ATRMk41/Q+PX07XQlRCRcE13a8neEz3F6we 08oWh2DnC4AXKbP+kuD9ZP6+5+x1H1zEzsFNBFXLn5EBEADn1959INH2cwYJv0tsxf5MUCgh Cj/CA/lc/LMthqQ773gauB9mN+F1rE9cyyXb6jyOGn+GUjMbnq1o121Vm0+neKHUCBtHyseB fDXHA6m4B3mUTWo13nid0e4AM71r0DS8+KYh6zvweLX/LL5kQS9GQeT+QNroXcC1NzWbitts 6TZ+IrPOwT1hfB4WNC+X2n4AzDqp3+ILiVST2DT4VBc11Gz6jijpC/KI5Al8ZDhRwG47LUiu Qmt3yqrmN63V9wzaPhC+xbwIsNZlLUvuRnmBPkTJwwrFRZvwu5GPHNndBjVpAfaSTOfppyKB Tccu2AXJXWAE1Xjh6GOC8mlFjZwLxWFqdPHR1n2aPVgoiTLk34LR/bXO+e0GpzFXT7enwyvF FFyAS0Nk1q/7EChPcbRbhJqEBpRNZemxmg55zC3GLvgLKd5A09MOM2BrMea+l0FUR+PuTenh 2YmnmLRTro6eZ/qYwWkCu8FFIw4pT0OUDMyLgi+GI1aMpVogTZJ70FgV0pUAlpmrzk/bLbRk F3TwgucpyPtcpmQtTkWSgDS50QG9DR/1As3LLLcNkwJBZzBG6PWbvcOyrwMQUF1nl4SSPV0L LH63+BrrHasfJzxKXzqgrW28CTAE2x8qi7e/6M/+XXhrsMYG+uaViM7n2je3qKe7ofum3s4v q7oFCPsOgwARAQABwsF8BBgBCAAmAhsMFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAmic2qsF CSZYCKEACgkQTd4Q9wD/g1oq0xAAsAnw/OmsERdtdwRfAMpC74/++2wh9RvVQ0x8xXvoGJwZ rk0Jmck1ABIM//5sWDo7eDHk1uEcc95pbP9XGU6ZgeiQeh06+0vRYILwDk8Q/y06TrTb1n4n 7FRwyskKU1UWnNW86lvWUJuGPABXjrkfL41RJttSJHF3M1C0u2BnM5VnDuPFQKzhRRktBMK4 GkWBvXlsHFhn8Ev0xvPE/G99RAg9ufNAxyq2lSzbUIwrY918KHlziBKwNyLoPn9kgHD3hRBa Yakz87WKUZd17ZnPMZiXriCWZxwPx7zs6cSAqcfcVucmdPiIlyG1K/HIk2LX63T6oO2Libzz 7/0i4+oIpvpK2X6zZ2cu0k2uNcEYm2xAb+xGmqwnPnHX/ac8lJEyzH3lh+pt2slI4VcPNnz+ vzYeBAS1S+VJc1pcJr3l7PRSQ4bv5sObZvezRdqEFB4tUIfSbDdEBCCvvEMBgoisDB8ceYxO cFAM8nBWrEmNU2vvIGJzjJ/NVYYIY0TgOc5bS9wh6jKHL2+chrfDW5neLJjY2x3snF8q7U9G EIbBfNHDlOV8SyhEjtX0DyKxQKioTYPOHcW9gdV5fhSz5tEv+ipqt4kIgWqBgzK8ePtDTqRM qZq457g1/SXSoSQi4jN+gsneqvlTJdzaEu1bJP0iv6ViVf15+qHuY5iojCz8fa0= In-Reply-To: <3aaa3e5d-7f66-40fc-a5b0-ea6a384a88a8@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 1/22/26 12:07, Dev Jain wrote: > > On 19/01/26 12:39 am, Shivank Garg wrote: >> When MADV_COLLAPSE is called on file-backed mappings (e.g., executable >> text sections), the pages may still be dirty from recent writes. >> collapse_file() will trigger async writeback and fail with >> SCAN_PAGE_DIRTY_OR_WRITEBACK (-EAGAIN). >> >> MADV_COLLAPSE is a synchronous operation where userspace expects >> immediate results. If the collapse fails due to dirty pages, perform >> synchronous writeback on the specific range and retry once. >> >> This avoids spurious failures for freshly written executables while >> avoiding unnecessary synchronous I/O for mappings that are already clean. >> >> Reported-by: Branden Moore >> Closes: https://lore.kernel.org/all/4e26fe5e-7374-467c-a333-9dd48f85d7cc@amd.com >> Fixes: 34488399fa08 ("mm/madvise: add file and shmem support to MADV_COLLAPSE") >> Suggested-by: David Hildenbrand >> Tested-by: Lance Yang >> Signed-off-by: Shivank Garg >> --- >> mm/khugepaged.c | 15 +++++++++++++++ >> 1 file changed, 15 insertions(+) >> >> diff --git a/mm/khugepaged.c b/mm/khugepaged.c >> index 219dfa2e523c..16582bdcb6ff 100644 >> --- a/mm/khugepaged.c >> +++ b/mm/khugepaged.c >> @@ -22,6 +22,7 @@ >> #include >> #include >> #include >> +#include >> >> #include >> #include "internal.h" >> @@ -2788,7 +2789,9 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start, >> >> for (addr = hstart; addr < hend; addr += HPAGE_PMD_SIZE) { >> int result = SCAN_FAIL; >> + bool triggered_wb = false; >> >> +retry: >> if (!mmap_locked) { >> cond_resched(); >> mmap_read_lock(mm); >> @@ -2809,8 +2812,20 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start, >> >> mmap_read_unlock(mm); >> mmap_locked = false; >> + *lock_dropped = true; >> result = hpage_collapse_scan_file(mm, addr, file, pgoff, >> cc); >> + >> + if (result == SCAN_PAGE_DIRTY_OR_WRITEBACK && !triggered_wb && >> + mapping_can_writeback(file->f_mapping)) { >> + loff_t lstart = (loff_t)pgoff << PAGE_SHIFT; >> + loff_t lend = lstart + HPAGE_PMD_SIZE - 1; >> + >> + filemap_write_and_wait_range(file->f_mapping, lstart, lend); > > So we don't care about the return value here because this is best-effort. > I really wish we had in our coding-style.rst to typecast such things to (void), > so we know explicitly that we are ignoring the return value, and not that the > function itself returns void. That makes functions like bitmap_and() hard (and ugly) to use that just return some value for the caller's convenience. For functions where we really want callers to think about this, we can enforce such checks through __must_check. Here, it's rather obvious that we don't care about the result as we only retry once to then give up. -- Cheers David