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Date: Thu, 11 Jun 2015 17:02:51 +0200
From: Ingo Molnar <mingo@kernel.org>
Subject: Re: [PATCH 2/4] mm: Send one IPI per CPU to TLB flush all entries
 after unmapping pages
Message-ID: <20150611150250.GA14086@gmail.com>
References: <1433871118-15207-1-git-send-email-mgorman@suse.de>
 <1433871118-15207-3-git-send-email-mgorman@suse.de>
 <20150610083332.GA25605@gmail.com>
 <20150610085950.GB26425@suse.de>
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To: Mel Gorman <mgorman@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>, Rik van Riel <riel@redhat.com>, Hugh Dickins <hughd@google.com>, Minchan Kim <minchan@kernel.org>, Dave Hansen <dave.hansen@intel.com>, Andi Kleen <andi@firstfloor.org>, H Peter Anvin <hpa@zytor.com>, Linus Torvalds <torvalds@linux-foundation.org>, Thomas Gleixner <tglx@linutronix.de>, Peter Zijlstra <a.p.zijlstra@chello.nl>, Linux-MM <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>


* Mel Gorman <mgorman@suse.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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