linux-kernel - Re: [PATCH RESEND v3 01/10] mm/vma: rename VMA_LOCK_OFFSET to VM_REFCNT_EXCLUDE_READERS

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Message-ID: <81f537e9-7058-4f9d-b50b-b5458dbf4479@lucifer.local>
Date: Fri, 23 Jan 2026 13:26:50 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Suren Baghdasaryan <surenb@...gle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...nel.org>,
        "Liam R . Howlett" <Liam.Howlett@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
        Michal Hocko <mhocko@...e.com>, Shakeel Butt <shakeel.butt@...ux.dev>,
        Jann Horn <jannh@...gle.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-rt-devel@...ts.linux.dev,
        Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
        Will Deacon <will@...nel.org>, Boqun Feng <boqun.feng@...il.com>,
        Waiman Long <longman@...hat.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Clark Williams <clrkwllms@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH RESEND v3 01/10] mm/vma: rename VMA_LOCK_OFFSET to
 VM_REFCNT_EXCLUDE_READERS_FLAG

On Thu, Jan 22, 2026 at 08:37:51AM -0800, Suren Baghdasaryan wrote:
> On Thu, Jan 22, 2026 at 5:02 AM Lorenzo Stoakes
> <lorenzo.stoakes@...cle.com> wrote:
> >
> > The VMA_LOCK_OFFSET value encodes a flag which vma->vm_refcnt is set to in
> > order to indicate that a VMA is in the process of having VMA read-locks
> > excluded in __vma_enter_locked() (that is, first checking if there are any
> > VMA read locks held, and if there are, waiting on them to be released).
> >
> > This happens when a VMA write lock is being established, or a VMA is being
> > marked detached and discovers that the VMA reference count is elevated due
> > to read-locks temporarily elevating the reference count only to discover a
> > VMA write lock is in place.
> >
> > The naming does not convey any of this, so rename VMA_LOCK_OFFSET to
> > VM_REFCNT_EXCLUDE_READERS_FLAG (with a sensible new prefix to differentiate
> > from the newly introduced VMA_*_BIT flags).
> >
> > Also rename VMA_REF_LIMIT to VM_REFCNT_LIMIT to make this consistent also.
> >
> > Update comments to reflect this.
> >
> > No functional change intended.
> >
> > Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
>
> Thanks for the cleanup Lorenzo, and sorry for the delay in reviewing
> your patches. I finally have some time and will try to finish my
> review today.
>
> Reviewed-by: Suren Baghdasaryan <surenb@...gle.com>

Thanks.

>
> > ---
> >  include/linux/mm_types.h  | 17 +++++++++++++----
> >  include/linux/mmap_lock.h | 14 ++++++++------
> >  mm/mmap_lock.c            | 17 ++++++++++-------
> >  3 files changed, 31 insertions(+), 17 deletions(-)
> >
> > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> > index 78950eb8926d..94de392ed3c5 100644
> > --- a/include/linux/mm_types.h
> > +++ b/include/linux/mm_types.h
> > @@ -752,8 +752,17 @@ static inline struct anon_vma_name *anon_vma_name_alloc(const char *name)
> >  }
> >  #endif
> >
> > -#define VMA_LOCK_OFFSET        0x40000000
> > -#define VMA_REF_LIMIT  (VMA_LOCK_OFFSET - 1)
> > +/*
> > + * WHile __vma_enter_locked() is working to ensure are no read-locks held on a
>
> s/WHile/While

Oops thanks. Will fix on respin.