linux-kernel - Re: [RFC PATCH 0/5] add process_madvise() flags to modify behaviour

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Message-ID: <bbf64de9-3b15-40b8-8b9a-dbf05fa3b4c9@lucifer.local>
Date: Tue, 20 May 2025 19:25:21 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: David Hildenbrand <david@...hat.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
        "Liam R . Howlett" <Liam.Howlett@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>, Jann Horn <jannh@...gle.com>,
        Arnd Bergmann <arnd@...db.de>, Christian Brauner <brauner@...nel.org>,
        linux-mm@...ck.org, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org, SeongJae Park <sj@...nel.org>,
        Usama Arif <usamaarif642@...il.com>
Subject: Re: [RFC PATCH 0/5] add process_madvise() flags to modify behaviour

On Tue, May 20, 2025 at 06:47:48PM +0100, Lorenzo Stoakes wrote:
> On Tue, May 20, 2025 at 05:28:35PM +0200, David Hildenbrand wrote:
[snip]
> > > 3. PMADV_SET_FORK_EXEC_DEFAULT
> > >
> > > It may be desirable for a user to specify that all VMAs mapped in a process
> > > address space default to having an madvise() behaviour established by
> > > default, in such a fashion as that this persists across fork/exec.
> >
> > This is very specific for MADV_HUGEPAGE only, so I wonder how we could
> > either avoid that flag or just make it clear that it shall stick around ...
> >

Sorry missed this bit.

I don't really like the idea of only for MADV_HUGEPAGE (and MADV_NOHUGEPAGE)
defaulting to doing this, I think that's far less clear than a user explicitly
asking for it, plus most users using process_madvise() wouldn't expect it.

So restricting this to these flags only and rejecting all others should cover
this off fine I think.

[snip]