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

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Message-ID: <2e6153c9-1729-463a-86b5-0973b3f56ea6@lucifer.local>
Date: Mon, 10 Nov 2025 14:05:40 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Matthew Wilcox <willy@...radead.org>
Cc: "David Hildenbrand (Red Hat)" <davidhildenbrandkernel@...il.com>,
        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 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