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Date:	Mon, 06 Oct 2014 07:07:37 -0700
From:	Laura Abbott <>
To:	Heesub Shin <>,
	Pintu Kumar <>,,,,,,,
Subject: Re: [PATCH 1/1] [ion]: system-heap use PAGE_ALLOC_COSTLY_ORDER for
 high order

On 10/6/2014 3:27 AM, Heesub Shin wrote:
> Hello Kumar,
> On 10/06/2014 05:31 PM, Pintu Kumar wrote:
>> The Android ion_system_heap uses allocation fallback mechanism
>> based on 8,4,0 order pages available in the system.
>> It changes gfp flags based on higher order allocation request.
>> This higher order value is hard-coded as 4, instead of using
>> the system defined higher order value.
>> Thus replacing this hard-coded value with PAGE_ALLOC_COSTLY_ORDER
>> which is defined as 3.
>> This will help mapping the higher order request in system heap with
>> the actual allocation request.
> Quite reasonable.
> Reviewed-by: Heesub Shin <>
> BTW, Anyone knows how the allocation order (8,4 and 0) was decided? I
> think only Google guys might know the answer.
> regards,
> heesub

My understanding was this was completely unrelated to the costly order
and was related to the page sizes corresponding to IOMMU page sizes
(1MB, 64K, 4K). This won't make a difference for the uncached page
pool case but for the not page pool case, I'm not sure if there would
be a benefit for trying to get 32K pages with some effort vs. just
going back to 4K pages.

Do you have any data/metrics that show a benefit from this patch?


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