linux-kernel - Re: [PATCH 1/2] mm/khugepaged: do synchronous writeback for MADV

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Message-ID: <39c8a4ed-53b5-48e3-baea-f67cc1e8be4f@amd.com>
Date: Mon, 10 Nov 2025 19:50:17 +0530
From: "Garg, Shivank" <shivankg@....com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Matthew Wilcox <willy@...radead.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 David Hildenbrand <david@...hat.com>, Zi Yan <ziy@...dia.com>,
 Baolin Wang <baolin.wang@...ux.alibaba.com>,
 "Liam R . Howlett" <Liam.Howlett@...cle.com>, Nico Pache
 <npache@...hat.com>, Ryan Roberts <ryan.roberts@....com>,
 Dev Jain <dev.jain@....com>, Barry Song <baohua@...nel.org>,
 Lance Yang <lance.yang@...ux.dev>, Steven Rostedt <rostedt@...dmis.org>,
 Masami Hiramatsu <mhiramat@...nel.org>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Zach O'Keefe <zokeefe@...gle.com>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
 Branden Moore <Branden.Moore@....com>
Subject: Re: [PATCH 1/2] mm/khugepaged: do synchronous writeback for
 MADV_COLLAPSE

On 11/10/2025 7:22 PM, Lorenzo Stoakes wrote:
> On Mon, Nov 10, 2025 at 01:47:10PM +0000, Matthew Wilcox wrote:
>> On Mon, Nov 10, 2025 at 11:32:53AM +0000, 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. The
>>
>> That explanation derails my brain entirely.  Text isn't writable!  How
>> can the pages be dirty and file-backed text?
> 
> Because they just compiled it and it's not been written back to disk yet :)

Hi, 

It's not about compilation. My binaries are already compiled.

The issue is copying those binary to a freshly mounted filesystem.
The page cache folios remain dirty until background writeback completes.

Reproduces 100% for me: fresh XFS/EXT4 mount -> copy binary -> execute -> MADV_COLLAPSE fails.

Detail logs: https://lore.kernel.org/all/0b84865c-5b23-4be6-9902-af9d5e63c182@amd.com

Thanks,
Shivank