linux-kernel - Re: [PATCH v3 3/8] mm: implement sticky VMA flags

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Message-ID: <d90275d5-5d56-42ac-b610-4162eb97fef2@lucifer.local>
Date: Tue, 18 Nov 2025 07:46:49 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: 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>,
        Zi Yan <ziy@...dia.com>, Baolin Wang <baolin.wang@...ux.alibaba.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>, 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 v3 3/8] mm: implement sticky VMA flags

On Mon, Nov 17, 2025 at 02:43:32PM -0800, Andrew Morton wrote:
> On Mon, 17 Nov 2025 20:02:03 +0000 Lorenzo Stoakes <lorenzo.stoakes@...cle.com> wrote:
>
> > Sorry to be a pain here, and can respin if it's easier, but can we update the
> > text of the comments below? As in discussion with Liam off-list we agreed that
> > the current wording is rather unclear and we can do a lot better.
> >
> > I provide the improved version inline below:
>
> np,
>
>  include/linux/mm.h               |    7 +++----
>  tools/testing/vma/vma_internal.h |    7 +++----
>  2 files changed, 6 insertions(+), 8 deletions(-)
>
> --- a/include/linux/mm.h~mm-implement-sticky-vma-flags-fix-2
> +++ a/include/linux/mm.h
> @@ -549,10 +549,9 @@ extern unsigned int kobjsize(const void
>   *                pressure on the memory system forcing the kernel to generate
>   *                new VMAs when old one could be extended instead.
>   *
> - *    VM_STICKY - If one VMA has flags which most be 'sticky', that is ones
> - *                which should propagate to all VMAs, but the other does not,
> - *                the merge should still proceed with the merge logic applying
> - *                sticky flags to the final VMA.
> + *    VM_STICKY - When merging VMAs, VMA flags must match, unless they are
> + *                'sticky'. If any sticky flags exist in either VMA, we simply
> + *                set all of them on the merged VMA.
>   */
>  #define VM_IGNORE_MERGE (VM_SOFTDIRTY | VM_STICKY)
>
> --- a/tools/testing/vma/vma_internal.h~mm-implement-sticky-vma-flags-fix-2
> +++ a/tools/testing/vma/vma_internal.h
> @@ -139,10 +139,9 @@ extern unsigned long dac_mmap_min_addr;
>   *                pressure on the memory system forcing the kernel to generate
>   *                new VMAs when old one could be extended instead.
>   *
> - *    VM_STICKY - If one VMA has flags which most be 'sticky', that is ones
> - *                which should propagate to all VMAs, but the other does not,
> - *                the merge should still proceed with the merge logic applying
> - *                sticky flags to the final VMA.
> + *    VM_STICKY - When merging VMAs, VMA flags must match, unless they are
> + *                'sticky'. If any sticky flags exist in either VMA, we simply
> + *                set all of them on the merged VMA.
>   */
>  #define VM_IGNORE_MERGE (VM_SOFTDIRTY | VM_STICKY)
>
> _
>

Thanks, much appreciated!

Despite your having very kindly done this, I apologise as I realise now after
all I have to respin... doh!

There was yet another typo as pointed out by Jane (and previously off-list,
Liam) plus Pedro (off-list) mentioned a silly mistake in my code fixup, and at
this point I think it'll keep us all a lot saner to just respin :>)

Cheers, Lorenzo