linux-kernel - Re: [PATCH 1/3] mm: introduce VM_MAYBE_GUARD and make visible for guard regions

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Message-ID: <a6062275-20a6-4014-beeb-6cf8aaf47410@lucifer.local>
Date: Thu, 30 Oct 2025 08:13:39 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Randy Dunlap <rdunlap@...radead.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
        Jonathan Corbet <corbet@....net>, David Hildenbrand <david@...hat.com>,
        "Liam R . Howlett" <Liam.Howlett@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
        Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Jann Horn <jannh@...gle.com>, Pedro Falcato <pfalcato@...e.de>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-mm@...ck.org,
        linux-trace-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        Andrei Vagin <avagin@...il.com>
Subject: Re: [PATCH 1/3] mm: introduce VM_MAYBE_GUARD and make visible for
 guard regions

On Wed, Oct 29, 2025 at 12:50:18PM -0700, Randy Dunlap wrote:
>
> On 10/29/25 9:50 AM, Lorenzo Stoakes wrote:
>
> > diff --git a/mm/memory.c b/mm/memory.c
> > index 4c3a7e09a159..a2c79ee43d68 100644
> > --- a/mm/memory.c
> > +++ b/mm/memory.c
> > @@ -1478,6 +1478,10 @@ vma_needs_copy(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma)
> >  	if (src_vma->anon_vma)
> >  		return true;
> >
> > +	/* Guard regions have momdified page tables that require copying. */
>
> 	                      modified

I appear to have entered some kind of typo nirvana in this series it seems :)

Thanks, will fix!

>
> > +	if (src_vma->vm_flags & VM_MAYBE_GUARD)
> > +		return true;
> > +
> >  	/*
> >  	 * Don't copy ptes where a page fault will fill them correctly.  Fork
> >  	 * becomes much lighter when there are big shared or private readonly
> --
> ~Randy
>

Cheers, Lorenzo