linux-kernel - Re: [PATCH v3 00/22] Add support for shared PTEs across processes

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Message-ID: <aL9DsGR8KimEQ44H@casper.infradead.org>
Date: Mon, 8 Sep 2025 21:59:28 +0100
From: Matthew Wilcox <willy@...radead.org>
To: David Hildenbrand <david@...hat.com>
Cc: Anthony Yznaga <anthony.yznaga@...cle.com>, linux-mm@...ck.org,
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Subject: Re: [PATCH v3 00/22] Add support for shared PTEs across processes

On Mon, Sep 08, 2025 at 10:32:22PM +0200, David Hildenbrand wrote:
> In the context of this series, how do we handle VMA-modifying functions like
> mprotect/some madvise/mlock/mempolicy/...? Are they currently blocked when
> applied to a mshare VMA?

I haven't been following this series recently, so I'm not sure what
Anthony will say.  My expectation is that the shared VMA is somewhat
transparent to these operations; that is they are faulty if they span
the boundary of the mshare VMA, but otherwise they pass through and
affect the shared VMAs.

That does raise the interesting question of how mlockall() affects
an mshare VMA.  I'm tempted to say that it should affect the shared
VMA, but reasonable people might well disagree with me and have
excellent arguments.

> And how are we handling other page table walkers that don't modify VMAs like
> MADV_DONTNEED, smaps, migrate_pages, ... etc?

I'd expect those to walk into the shared region too.