Re: [Intel-IOMMU 02/10] Library routine for pre-allocat pool handling

["Siddha, Suresh B" <suresh.b.siddha@intel.com>]

On Mon, Jun 11, 2007 at 06:55:46PM -0700, Arjan van de Ven wrote:
> Andrew Morton wrote:
> >On Mon, 11 Jun 2007 18:10:40 -0700 Arjan van de Ven 
> ><arjan@linux.intel.com> wrote:
> >
> >>Andrew Morton wrote:
> >>>>Where as resource pool is exactly opposite of mempool, where each 
> >>>>time it looks for an object in the pool and if it exist then we 
> >>>>return that object else we try to get the memory for OS while 
> >>>>scheduling the work to grow the pool objects. In fact, the  work
> >>>>is schedule to grow the pool when the low threshold point is hit.
> >>>I realise all that.  But I'd have thought that the mempool approach is
> >>>actually better: use the page allocator and only deplete your reserve 
> >>>pool
> >>>when the page allocator fails.
> >>the problem with that is that if anything downstream from the iommu 
> >>layer ALSO needs memory, we've now eaten up the last free page and 
> >>things go splat.
> >
> >If that happens, we still have the mempool reserve to fall back to.
> 
> we do, except that we just ate the memory the downstream code would 
> use and get ... so THAT can't get any.

Then this problem can happen, irrespective of the changes we are
reviewing in this patch set. Is n't it?

thanks,
suresh
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