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

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Message-ID: <69884a4d-60cb-4a66-a225-38d3a17712c6@gmail.com>
Date: Mon, 10 Nov 2025 15:54:55 +0100
From: "David Hildenbrand (Red Hat)" <davidhildenbrandkernel@...il.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Matthew Wilcox <willy@...radead.org>
Cc: Shivank Garg <shivankg@....com>, Andrew Morton
 <akpm@...ux-foundation.org>, 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 10.11.25 15:05, Lorenzo Stoakes wrote:
> On Mon, Nov 10, 2025 at 02:03:43PM +0000, Matthew Wilcox wrote:
>> On Mon, Nov 10, 2025 at 03:00:32PM +0100, David Hildenbrand (Red Hat) wrote:
>>> On 10.11.25 14:47, 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?
>>>
>>> Files are writable :)
>>
>> Well, if you're root ...
>>
>> -rwxr-xr-x 1 root root 158632 Jun  4 11:14 /bin/ls
>>
> 
> gcc foo.c -o foo && ./foo
> 
> Is more the issue I think

Yeah, that's my understanding as well. I guess stuff like 
package/container updates might similarly trigger it.