linux-kernel - Re: [PATCH] [BUGFIX] mm: hugepages can cause negative commitlimit

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Message-Id: <20110520130411.d1e0baef.akpm@linux-foundation.org>
Date:	Fri, 20 May 2011 13:04:11 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Russ Anderson <rja@....com>
Cc:	Rafael Aquini <aquini@...ux.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	linux-mm <linux-mm@...ck.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Christoph Lameter <cl@...ux.com>
Subject: Re: [PATCH] [BUGFIX] mm: hugepages can cause negative commitlimit

On Thu, 19 May 2011 17:11:01 -0500
Russ Anderson <rja@....com> wrote:

> OK, I see your point.  The root problem is hugepages allocated at boot are
> subtracted from totalram_pages but hugepages allocated at run time are not.
> Correct me if I've mistate it or are other conditions.
> 
> By "allocated at run time" I mean "echo 1 > /proc/sys/vm/nr_hugepages".
> That allocation will not change totalram_pages but will change
> hugetlb_total_pages().
> 
> How best to fix this inconsistency?  Should totalram_pages include or exclude
> hugepages?  What are the implications?

The problem is that hugetlb_total_pages() is trying to account for two
different things, while totalram_pages accounts for only one of those
things, yes?

One fix would be to stop accounting for huge pages in totalram_pages
altogether.  That might break other things so careful checking would be
needed.

Or we stop accounting for the boot-time allocated huge pages in
hugetlb_total_pages().  Split the two things apart altogether and
account for boot-time allocated and runtime-allocated pages separately.  This
souds saner to me - it reflects what's actually happening in the kernel.
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