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

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Message-ID: <20241213183546.GB12338@noisy.programming.kicks-ass.net>
Date: Fri, 13 Dec 2024 19:35:46 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Suren Baghdasaryan <surenb@...gle.com>
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 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.