linux-kernel - Re: [PATCH v2] mm: per-thread vma caching

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Message-ID: <20140226085518.GI3104@twins.programming.kicks-ass.net>
Date:	Wed, 26 Feb 2014 09:55:18 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Davidlohr Bueso <davidlohr@...com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Michel Lespinasse <walken@...gle.com>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>, aswin@...com,
	scott.norton@...com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mm: per-thread vma caching

On Wed, Feb 26, 2014 at 09:50:48AM +0100, Peter Zijlstra wrote:
> On Tue, Feb 25, 2014 at 10:16:46AM -0800, Davidlohr Bueso wrote:
> > +void vmacache_invalidate_all(void)
> > +{
> > +	struct task_struct *g, *p;
> > +
> > +	rcu_read_lock();
> > +	for_each_process_thread(g, p) {
> > +		/*
> > +		 * Only flush the vmacache pointers as the
> > +		 * mm seqnum is already set and curr's will
> > +		 * be set upon invalidation when the next
> > +		 * lookup is done.
> > +		 */
> > +		memset(p->vmacache, 0, sizeof(p->vmacache));
> > +	}
> > +	rcu_read_unlock();
> > +}
> 
> With all the things being said on this particular piece already; I
> wanted to add that the iteration there is incomplete; we can clone()
> using CLONE_VM without using CLONE_THREAD.
> 
> Its not common, but it can be done. In that case the above iteration
> will miss a task that shares the same mm.

Bugger; n/m that. I just spotted that it's yet another way to iterate
all tasks in the system.

Of course we need multiple macros to do this :/

Pretty horrifically expensive though.
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