Subject: Re: [PATCH 1/6] sparc64: Add FORCE_MAX_ZONEORDER and default to 13
To: David Miller <davem@davemloft.net>
References: <1476123127-24314-1-git-send-email-tushar.n.dave@oracle.com>
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 <20161024.134543.843902561898603557.davem@davemloft.net>
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        vgupta@synopsys.com, robin.murphy@arm.com, jroedel@suse.de,
        egtvedt@samfundet.no, krzk@kernel.org, rkuo@codeaurora.org,
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From: tndave <tushar.n.dave@oracle.com>
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Date: Mon, 24 Oct 2016 11:31:14 -0700
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On 10/24/2016 10:45 AM, David Miller wrote:
> From: Tushar Dave <tushar.n.dave@oracle.com>
> Date: Mon, 10 Oct 2016 11:12:02 -0700
>
>> From: Dave Kleikamp <dave.kleikamp@oracle.com>
>>
>> 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@oracle.com>
>> Signed-off-by: Tushar Dave <tushar.n.dave@oracle.com>
>
> 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

>