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Re: [regression v4.0-rc1] mm: IPIs from TLB flushes causing significant

To: Ingo Molnar <mingo@xxxxxxxxxx>
Subject: Re: [regression v4.0-rc1] mm: IPIs from TLB flushes causing significant performance degradation.
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Thu, 5 Mar 2015 10:51:26 +1100
Cc: Mel Gorman <mgorman@xxxxxxx>, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, Matt B <jackdachef@xxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, linux-mm <linux-mm@xxxxxxxxx>, xfs@xxxxxxxxxxx
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In-reply-to: <20150304233544.GA24733@xxxxxxxxx>
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On Thu, Mar 05, 2015 at 12:35:45AM +0100, Ingo Molnar wrote:
> * Dave Chinner <david@xxxxxxxxxxxxx> wrote:
> > > After going through the series again, I did not spot why there is 
> > > a difference. It's functionally similar and I would hate the 
> > > theory that this is somehow hardware related due to the use of 
> > > bits it takes action on.
> > 
> > I doubt it's hardware related - I'm testing inside a VM, [...]
> That might be significant, I doubt Mel considered KVM's interpretation 
> of pte details?

I did actaully mention that before:

| I am running a fake-numa=4 config on this test VM so it's got 4
| nodes of 4p/4GB RAM each.

but I think it got snipped before Mel was cc'd.

Perhaps size of the nodes is relevant, too, because the steady state
phase 3 memory usage is 5-6GB when this problem first shows up, and
then continues into phase 4 where memory usage grows again and peaks
at ~10GB....


Dave Chinner

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