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: <9f480987-a4a5-4c5b-bce3-a85bdcb487c0@lucifer.local>
Date: Fri, 23 Jan 2026 13:52:44 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...nel.org>,
        "Liam R . Howlett" <Liam.Howlett@...cle.com>,
        Mike Rapoport <rppt@...nel.org>,
        Suren Baghdasaryan <surenb@...gle.com>, 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 04:29:35PM +0000, Lorenzo Stoakes wrote:
> On Thu, Jan 22, 2026 at 05:26:13PM +0100, Vlastimil Babka wrote:
> > On 1/22/26 14:01, Lorenzo Stoakes 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>
> >
> > Reviewed-by: Vlastimil Babka <vbabka@...e.cz>
> >
> > git grep tells me VMA_LOCK_OFFSET is still used in
> > tools/testing/vma/vma_internal.h but I guess it doesn't break the tests?
> >
>
> No :) I update it later in the series but it doesn't break the tests so no
> bisection hazard.

Apologies I was mistaken, however there is no impact on the tests and the VMA
flags/mmap_prepare series I sent makes radical changes there so I will update
this at a later date I think to keep everything sane.

todo++; :)

Cheers, Lorenzo