linux-kernel - Re: [PATCH] regression: vmalloc easily fail.

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Date:	Wed, 29 Oct 2008 00:29:44 +0100
From:	Nick Piggin <npiggin@...e.de>
To:	Glauber Costa <glommer@...hat.com>
Cc:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org, avi@...hat.com,
	aliguori@...emonkey.ws, Jeremy Fitzhardinge <jeremy@...p.org>,
	Krzysztof Helt <krzysztof.h1@...zta.fm>
Subject: Re: [PATCH] regression: vmalloc easily fail.

On Tue, Oct 28, 2008 at 08:55:13PM -0200, Glauber Costa wrote:
> Commit db64fe02258f1507e13fe5212a989922323685ce broke
> KVM (the symptom) for me. The cause is that vmalloc
> allocations fail, despite of the fact that /proc/meminfo
> shows plenty of vmalloc space available.
> 
> After some investigation, it seems to me that the current
> way to compute the next addr in the rb-tree transversal
> leaves a spare page between each allocation. After a few
> allocations, regardless of their size, we run out of vmalloc
> space.

Right... that was to add a guard page like the old vmalloc allocator.
vmallocs still add their extra page too, so most of them will have
a 2 page guard area, but I didn't think this would hurt significantly.

I'm not against the patch, but I wonder exactly what is filling it up
and how? (can you look at the vmalloc proc function to find out?)

> 
> Signed-off-by: Glauber Costa <glommer@...hat.com>
> Cc: Jeremy Fitzhardinge <jeremy@...p.org>
> Cc: Krzysztof Helt <krzysztof.h1@...zta.fm>
> ---
>  mm/vmalloc.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 0365369..a33b0d1 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -363,7 +363,7 @@ retry:
>  		}
>  
>  		while (addr + size >= first->va_start && addr + size <= vend) {
> -			addr = ALIGN(first->va_end + PAGE_SIZE, align);
> +			addr = ALIGN(first->va_end, align);
>  
>  			n = rb_next(&first->rb_node);
>  			if (n)
> -- 
> 1.5.6.5
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