linux-kernel - Why does ion_cma_allocate need GFP_HIGHUSER

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Message-ID: <54645B38.10603@lge.com>
Date:	Thu, 13 Nov 2014 16:18:16 +0900
From:	Gioh Kim <gioh.kim@....com>
To:	Colin Cross <ccross@...roid.com>, Joonsoo Kim <js1304@...il.com>
CC:	John Stultz <john.stultz@...aro.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	lauraa@...eaurora.org, devel@...verdev.osuosl.org,
	linux-kernel@...r.kernel.org,
	"이건호/책임연구원/SW Platform(연)AOT팀(gunho.lee@....com)" 
	<gunho.lee@....com>
Subject: Why does ion_cma_allocate need GFP_HIGHUSER | __GFP_ZERO flags?

Hi,

I'm wondering why dma_alloc_coherent needs GFP_HIGHUSER | __GFP_ZERO flags in ion_cma_allocate().

I think dma_alloc_coherent can go to __dma_alloc if the system has CMA area.
If __GFP_WAIT flag is set, it allocates memory from atomic pool.
So I think calling dma_alloc_coherent with __GFP_WAIT is enough.

And can I get zero-filled-memory from CMA if I set __GFP_ZERO?

-- 
Thanks,
Gioh Kim
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