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Date: Tue, 09 Jun 2015 16:01:46 -0400
From: Rik van Riel <riel@redhat.com>
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To: Mel Gorman <mgorman@suse.de>, Andrew Morton <akpm@linux-foundation.org>
CC: 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>, Ingo Molnar <mingo@kernel.org>,
        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>
Subject: Re: [PATCH 2/4] mm: Send one IPI per CPU to TLB flush all entries
 after unmapping pages
References: <1433871118-15207-1-git-send-email-mgorman@suse.de> <1433871118-15207-3-git-send-email-mgorman@suse.de>
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On 06/09/2015 01:31 PM, Mel Gorman wrote:
> An IPI is sent to flush remote TLBs when a page is unmapped that was
> potentially accesssed by other CPUs. There are many circumstances where
> this happens but the obvious one is kswapd reclaiming pages belonging to
> a running process as kswapd and the task are likely running on separate CPUs.

> It's still a noticeable improvement with vmstat showing interrupts went
> from roughly 500K per second to 45K per second.
> 
> The patch will have no impact on workloads with no memory pressure or
> have relatively few mapped pages. It will have an unpredictable impact
> on the workload running on the CPU being flushed as it'll depend on how
> many TLB entries need to be refilled and how long that takes. Worst case,
> the TLB will be completely cleared of active entries when the target PFNs
> were not resident at all.
> 
> Signed-off-by: Mel Gorman <mgorman@suse.de>

Reviewed-by: Rik van Riel <riel@redhat.com>


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