Re: GFP_ATOMIC versus GFP_NOWAIT

Andi Kleen
2009-11-13T09:17:41Z

Dan Williams <dan.j.williams@intel.com> writes:

> Looking through the tree it seems that almost all drivers that need to
> allocate memory in atomic contexts use GFP_ATOMIC. I have been asking
> dmaengine device driver authors to switch their atomic allocations to
> GFP_NOWAIT. The rationale being that in most cases a dma device is
> either offloading an operation that will automatically fallback to
> software when the descriptor allocation fails, or we can simply poll
> and wait for the dma device to release some in use descriptors. So it
> does not make sense to grab from the emergency pools when the result
> of an allocation failure is some additional cpu overhead. Am I
> correct in my nagging, and should this idea be spread outside of
> drivers/dma/ to cut down on GFP_ATOMIC usage, or is this not a big
> issue?

It's probably hard to find a good global priority order between
the various allocators, depending on how much the fallback costs.
But in principle it sounds like a good idea.

-Andi

--
ak@linux.intel.com -- Speaking for myself only.