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Date: Wed, 4 Apr 2007 13:49:33 -0500
From: Anton Blanchard <anton@...ba.org>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Ulrich Drepper <drepper@...hat.com>,
Andi Kleen <andi@...stfloor.org>,
Rik van Riel <riel@...hat.com>,
Linux Kernel <linux-kernel@...r.kernel.org>,
Jakub Jelinek <jakub@...hat.com>, linux-mm@...ck.org,
Hugh Dickins <hugh@...itas.com>
Subject: Re: missing madvise functionality
Hi,
> Oh. I was assuming that we'd want to unmap these pages from pagetables and
> mark then super-easily-reclaimable. So a later touch would incur a minor
> fault.
>
> But you think that we should leave them mapped into pagetables so no such
> fault occurs.
That would be very nice. The issues are not limited to threaded apps,
we have seen performance problems with single threaded HPC applications
that do a lot of large malloc/frees. It turns out the continual set up
and tear down of pagetables when malloc uses mmap/free is a problem. At
the moment the workaround is:
export MALLOC_MMAP_MAX_=0 MALLOC_TRIM_THRESHOLD_=-1
which forces glibc malloc to use brk instead of mmap/free. Of course brk
is good for keeping pagetables around but bad for keeping memory usage
down.
Anton
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