Re: [PATCH 1/6] sparc64: Add FORCE_MAX_ZONEORDER and default to 13

[tndave]

On 10/24/2016 10:45 AM, David Miller wrote:
> From: Tushar Dave <tushar.n.dave@xxxxxxxxxx>
> Date: Mon, 10 Oct 2016 11:12:02 -0700
>
> > From: Dave Kleikamp <dave.kleikamp@xxxxxxxxxx>
> >
> > This change allows ATU (new IOMMU) in SPARC systems to request
> > large (32M) contiguous memory during boot for creating IOTSB backing
> > store.
> >
> > Signed-off-by: Dave Kleikamp <dave.kleikamp@xxxxxxxxxx>
> > Signed-off-by: Tushar Dave <tushar.n.dave@xxxxxxxxxx>
>
> If you need 32MB allocations, wouldn't a max zone order of 12 be
> sufficient?  (8K << 12 == 32MB)
Yes, but config FORCE_MAX_ZONEORDER is actually maximum order plus one.
For example, a value of 13 means that the largest free memory block is
2^12 pages. For 32MB we need 2^12 8K pages, hence FORCE_MAX_ZONEORDER
must be MAX_ORDER + 1 i.e. 13.

Thanks.

-Tushar

>