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: <3ac3933c-8fc6-46ee-adae-e7609b5f6d4d@lucifer.local>
Date: Thu, 22 Jan 2026 16:29:35 +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 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.

Cheers, Lorenzo