linux-kernel - Re: [PATCH 3/4] mm: replace rw_semaphore with atomic_t in vma

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Message-ID: <CAJuCfpG5LJeM3OmkUv7MGr6tVVGFJ10j5T1TJMdhq6p6yyCz2Q@mail.gmail.com>
Date: Fri, 13 Dec 2024 10:37:16 -0800
From: Suren Baghdasaryan <surenb@...gle.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Matthew Wilcox <willy@...radead.org>, akpm@...ux-foundation.org, liam.howlett@...cle.com, 
	lorenzo.stoakes@...cle.com, mhocko@...e.com, vbabka@...e.cz, 
	hannes@...xchg.org, mjguzik@...il.com, oliver.sang@...el.com, 
	mgorman@...hsingularity.net, david@...hat.com, peterx@...hat.com, 
	oleg@...hat.com, dave@...olabs.net, paulmck@...nel.org, brauner@...nel.org, 
	dhowells@...hat.com, hdanton@...a.com, hughd@...gle.com, minchan@...gle.com, 
	jannh@...gle.com, shakeel.butt@...ux.dev, souravpanda@...gle.com, 
	pasha.tatashin@...een.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org, 
	kernel-team@...roid.com
Subject: Re: [PATCH 3/4] mm: replace rw_semaphore with atomic_t in vma_lock

On Fri, Dec 13, 2024 at 10:35 AM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Fri, Dec 13, 2024 at 09:45:33AM -0800, Suren Baghdasaryan wrote:
> > On Fri, Dec 13, 2024 at 1:57 AM Peter Zijlstra <peterz@...radead.org> wrote:
> > >
> > > On Thu, Dec 12, 2024 at 08:48:52PM -0800, Suren Baghdasaryan wrote:
> > >
> > > > I'm not sure if this is the best way to deal with this circular
> > > > dependency. Any other ideas?
> > >
> > > Move the waiting into an out-of-line slow-path?
> > >
> > >   if (atomic_read(&vma->refcnt) != 2)
> > >     __vma_write_start_wait(mm, vma);
> >
> > The problem is not a function but the addition of struct rcuwait into
>
> Durr, in my brain that was a struct task_struct pointer, totally forgot
> we had a type there. Yeah, as Willy says, move it to compiler_types.h or
> somesuch.

Got it. Thank you both!