Messages in this thread | | | Date | Tue, 28 Oct 2008 14:42:55 -0700 | From | Arjan van de Ven <> | Subject | Re: [PATCH] regression: vmalloc easily fail. |
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On Tue, 28 Oct 2008 14:22:16 -0700 Roland Dreier <rdreier@cisco.com> wrote:
> > 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?
I suspect it's a case of off-by-one... ALIGN() might round down, and the "+ (PAGE_SIZE-1)" was there to make it round up. Except for that missing -1 ...
-- Arjan van de Ven Intel Open Source Technology Centre For development, discussion and tips for power savings, visit http://www.lesswatts.org
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