linux-kernel - Re: [PATCH] anon_vmas: Convert the rwsem to an rwlock

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Date:	Mon, 30 Sep 2013 21:16:00 +0200
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Ingo Molnar <mingo@...nel.org>, Waiman Long <Waiman.Long@...com>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Rik van Riel <riel@...hat.com>,
	Peter Hurley <peter@...leysoftware.com>,
	Davidlohr Bueso <davidlohr.bueso@...com>,
	Alex Shi <alex.shi@...el.com>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Matthew R Wilcox <matthew.r.wilcox@...el.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Michel Lespinasse <walken@...gle.com>,
	Andi Kleen <andi@...stfloor.org>,
	"Chandramouleeswaran, Aswin" <aswin@...com>,
	"Norton, Scott J" <scott.norton@...com>,
	Haggai Eran <haggaie@...lanox.com>,
	Sagi Grimberg <sagig@...lanox.com>,
	Or Gerlitz <ogerlitz@...lanox.com>,
	Jerome Glisse <jglisse@...hat.com>
Subject: Re: [PATCH] anon_vmas: Convert the rwsem to an rwlock_t

On Mon, Sep 30, 2013 at 09:26:21AM -0700, Linus Torvalds wrote:
> On Mon, Sep 30, 2013 at 1:52 AM, Andrea Arcangeli <aarcange@...hat.com> wrote:
> >
> > Sorry having to break the party but the sleepable locks for anon_vma
> > and i_mmap_mutex are now requirement for the "pageable RDMA" effort
> > recently achieved upstream by mellanox with the MMU notifier.
> 
> I'll happily break that.

Unless a solution is found that could allow to invalidate secondary
MMUs with a spinlock/rwlock for anon_vma->lock/i_mmap_lock, would it
be acceptable to switch between spinlock/rwlock mutex/rwsem through a
config option? option CONFIG_SLEEPABLE_RMAP, implicitly selected by
CONFIG_SLEEPABLE_MMU_NOTIFIER, in turn selected by the RDMA and nvidia
drivers if they're built (ideally nvidia drivers will figure out how
to avoid scheduling).

I mean it only requires a wrapping header file, aside from the header
file it wouldn't be a much bigger patch than the one posted already.

It would be much easier to switch between spinning and sleeping locks
to keep benchmarking different scenarios too.
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