linux-kernel - Re: [PATCH v4] mm: per-thread vma caching

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Message-ID: <1394335345.11969.34.camel@buesod1.americas.hpqcorp.net>
Date:	Sat, 08 Mar 2014 19:22:25 -0800
From:	Davidlohr Bueso <davidlohr@...com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Michel Lespinasse <walken@...gle.com>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	Davidlohr Bueso <davi@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4] mm: per-thread vma caching

On Sat, 2014-03-08 at 12:02 -0800, Linus Torvalds wrote:
> On Sat, Mar 8, 2014 at 11:44 AM, Oleg Nesterov <oleg@...hat.com> wrote:
> >
> > Sure. But another thread or CLONE_VM task can do vmacache_invalidate(),
> > hit vmacache_seqnum == 0 and call vmacache_flush_all() to solve the
> > problem with potential overflow.
> 
> How?
> 
> Any invalidation is supposed to hold the mm semaphore for writing. And
> we should have it for reading.

Yes, invalidations are always with the write lock held. In any case it's
a good candidate to use verify_mm_writelocked(), even if it's only under
debug environments.

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