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

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Date:	Sat, 8 Mar 2014 20:57:05 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Davidlohr Bueso <davidlohr@...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@...r.kernel.org
Subject: Re: [PATCH v4] mm: per-thread vma caching

looks like I removed lkml somehow, resend...

On 03/08, Linus Torvalds wrote:
>
> On Sat, Mar 8, 2014 at 10:40 AM, Oleg Nesterov <oleg@...hat.com> wrote:
> >
> > It seems this should be moved into copy_mm(), CLONE_VM needs to invalidate
> > ->vmacache too.
>
> No it doesn't. CLONE_VM doesn't change any of the vma lists,

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.

> so
> there's no reason to invalidate anything.
>
> > dup_task_struct() also copies vmacache_seqnum/vmacache, but the new thread
> > is not yet visible to vmacache_flush_all().
>
> So either the new task struct will share the mm, in which case the
> cache entries are fine

Not if they should be flushed by vmacache_flush_all() above.

Oleg.

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