linux-kernel - Re: [PATCH 1/1] [ion]: system-heap use PAGE_ALLOC_COSTLY

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Date:	Mon, 06 Oct 2014 07:07:37 -0700
From:	Laura Abbott <lauraa@...eaurora.org>
To:	Heesub Shin <heesub.shin@...sung.com>,
	Pintu Kumar <pintu.k@...sung.com>, akpm@...ux-foundation.org,
	gregkh@...uxfoundation.org, john.stultz@...aro.org,
	rebecca@...roid.com, ccross@...roid.com,
	devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org
CC:	iqbal.ams@...sung.com, pintu_agarwal@...oo.com,
	vishnu.ps@...sung.com
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 <heesub.shin@...sung.com>
>
> 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?

Thanks,
Laura

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