From: Roland Dreier <rdreier@cisco.com>
To: Avi Kivity <avi@redhat.com>
Cc: Glauber Costa <glommer@redhat.com>, linux-kernel@vger.kernel.org,
       kvm@vger.kernel.org, aliguori@codemonkey.ws, npiggin@suse.de,
       Jeremy Fitzhardinge <jeremy@goop.org>,
       Krzysztof Helt <krzysztof.h1@poczta.fm>
Subject: Re: [PATCH] regression: vmalloc easily fail.
References: <1225234513-3996-1-git-send-email-glommer@redhat.com>
	<49077E1A.5080105@redhat.com>
Date: Tue, 28 Oct 2008 14:22:16 -0700
In-Reply-To: <49077E1A.5080105@redhat.com> (Avi Kivity's message of "Tue, 28
	Oct 2008 23:03:22 +0200")
Message-ID: <ada7i7so1o7.fsf@cisco.com>
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 > I'm guessing that the missing comment explains that this is
 > intentional, to trap buffer overflows?

Actually, speaking of comments, it's interesting that
__get_vm_area_node() -- which is called from vmalloc() -- does:

	/*
	 * We always allocate a guard page.
	 */
	size += PAGE_SIZE;

	va = alloc_vmap_area(size, align, start, end, node, gfp_mask);

and alloc_vmap_area() adds another PAGE_SIZE, as the original email
pointed out:

		while (addr + size >= first->va_start && addr + size <= vend) {
			addr = ALIGN(first->va_end + PAGE_SIZE, align);

I wonder if the double padding is causing a problem when things get too
fragmented?

 - R.
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