linux-kernel - Re: GFP_ATOMIC versus GFP

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Message-ID: <87k4xuu6kv.fsf@basil.nowhere.org>
Date:	Fri, 13 Nov 2009 10:17:36 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Dan Williams <dan.j.williams@...el.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-mm@...ck.org
Subject: Re: GFP_ATOMIC versus GFP_NOWAIT

Dan Williams <dan.j.williams@...el.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@...ux.intel.com -- Speaking for myself only.
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