linux-kernel - Re: [PATCH 2/4] mm: Send one IPI per CPU to TLB flush all entries after unmapping pages

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Message-ID: <20150611150250.GA14086@gmail.com>
Date:	Thu, 11 Jun 2015 17:02:51 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Hugh Dickins <hughd@...gle.com>,
	Minchan Kim <minchan@...nel.org>,
	Dave Hansen <dave.hansen@...el.com>,
	Andi Kleen <andi@...stfloor.org>,
	H Peter Anvin <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/4] mm: Send one IPI per CPU to TLB flush all entries
 after unmapping pages


* Mel Gorman <mgorman@...e.de> wrote:

> > In the full-flushing case (v6 without patch 4) the batching limit is 
> > 'infinite', we'll batch as long as possible, right?
> 
> No because we must flush before pages are freed so the maximum batching is 
> related to SWAP_CLUSTER_MAX. If we free a page before the flush then in theory 
> the page can be reallocated and a stale TLB entry can allow access to unrelated 
> data. It would be almost impossible to trigger corruption this way but it's a 
> concern.

Well, could we say double SWAP_CLUSTER_MAX to further reduce the IPI rate?

Thanks,

	Ingo
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