Date: Fri, 22 Jun 2012 14:47:14 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: "John Stoffel" <john@stoffel.org>
Cc: Rik van Riel <riel@surriel.com>, linux-mm@kvack.org, aarcange@redhat.com,
        peterz@infradead.org, minchan@gmail.com, kosaki.motohiro@gmail.com,
        andi@firstfloor.org, hannes@cmpxchg.org, mel@csn.ul.ie,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH -mm v2 00/11] mm: scalable and unified
 arch_get_unmapped_area
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On Fri, 22 Jun 2012 10:24:58 -0400
"John Stoffel" <john@stoffel.org> wrote:

> >>>>> "Rik" == Rik van Riel <riel@surriel.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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