Re: [PATCH 1/1] [ion]: system-heap use PAGE_ALLOC_COSTLY_ORDER for high order

[Laura Abbott]

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@xxxxxxxxxxx>
>
> 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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