linux-kernel - Re: [PATCH -mm v2 00/11] mm: scalable and unified arch_get_unmapped

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Date:	Fri, 22 Jun 2012 14:47:14 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"John Stoffel" <john@...ffel.org>
Cc:	Rik van Riel <riel@...riel.com>, linux-mm@...ck.org,
	aarcange@...hat.com, peterz@...radead.org, minchan@...il.com,
	kosaki.motohiro@...il.com, andi@...stfloor.org, hannes@...xchg.org,
	mel@....ul.ie, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -mm v2 00/11] mm: scalable and unified
 arch_get_unmapped_area

On Fri, 22 Jun 2012 10:24:58 -0400
"John Stoffel" <john@...ffel.org> wrote:

> >>>>> "Rik" == Rik van Riel <riel@...riel.com> writes:
> 
> Rik> A long time ago, we decided to limit the number of VMAs per
> Rik> process to 64k. As it turns out, there actually are programs
> Rik> using tens of thousands of VMAs.
> 
> 
> Rik> Performance
> 
> Rik> Testing performance with a benchmark that allocates tens
> Rik> of thousands of VMAs, unmaps them and mmaps them some more
> Rik> in a loop, shows promising results.
> 
> How are the numbers for applications which only map a few VMAs?  Is
> there any impact there?
> 

Johannes did a test for that: https://lkml.org/lkml/2012/6/22/219

Some regression with such a workload is unavoidable, I expect.  We have
to work out whether the pros outweigh the cons.  This involves handwaving.
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