linux-kernel - Re: [PATCH RESEND v3 03/10] mm/vma: rename is_vma_write

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Message-ID: <168cbc6c-5f7b-4324-8d45-d9033613a67e@suse.cz>
Date: Fri, 23 Jan 2026 09:24:54 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Suren Baghdasaryan <surenb@...gle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 David Hildenbrand <david@...nel.org>,
 "Liam R . Howlett" <Liam.Howlett@...cle.com>, 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 03/10] mm/vma: rename is_vma_write_only(),
 separate out shared refcount put

On 1/22/26 20:31, Suren Baghdasaryan wrote:
>> > +     int oldcnt;
>> > +     bool detached;
>> > +
>> > +     detached = __refcount_dec_and_test(&vma->vm_refcnt, &oldcnt);
>> > +     if (refcnt)
>> > +             *refcnt = oldcnt - 1;
>> > +     return detached;
> 
> IIUC there is always a connection between detached and *refcnt
> resulting value. If detached==true then the resulting *refcnt has to
> be 0. If so, __vma_refcount_put() can simply return (oldcnt - 1) as
> new count:
> 
> static inline int __vma_refcount_put(struct vm_area_struct *vma)
> {
>        int oldcnt;
> 
>        __refcount_dec_and_test(&vma->vm_refcnt, &oldcnt);
>        return oldcnt - 1;
> }
> 
> And later:
> 
> newcnt = __vma_refcount_put(&vma->vm_refcnt);
> detached = newcnt == 0;

If we go that way (both ways are fine with me) I'd suggest we rename the
function to __vma_refcount_put_return to make this more obvious. (c.f.
atomic_dec_return, lockref_put_return).