Re: [PATCH 00/28] Swap over NFS -v16

Pekka Enberg
2008-02-27T08:05:07Z

Hi Peter,

On Wed, Feb 27, 2008 at 9:58 AM, Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:
> > 1/ I note there is no way to tell if memory returned by kmalloc is
> > from the emergency reserve - which contrasts with alloc_page
> > which does make that information available through page->reserve.
> > This seems a slightly unfortunate aspect of the interface.
>
> Yes, but alas there is no room to store such information in kmalloc().
> That is, in a sane way. I think it was Daniel Phillips who suggested
> encoding it in the return pointer by flipping the low bit - but that is
> just too ugly and breaks all current kmalloc sites to boot.

Why can't you add a kmem_is_emergency() to SLUB that looks up the
cache/slab/page (whatever is the smallest unit of the emergency pool
here) for the object and use that?