[RFC] ARM hugetlb support

[Catalin Marinas]

On 1 February 2012 01:56, bill4carson <bill4carson at gmail.com> wrote:
> On 2012年01月31日 17:29, Catalin Marinas wrote:
>> It also doesn't
>> help much with the TLB hit rate since the micro-TLB most likely only
>> support 1MB sections.
>
> I am afraid I can't agree with you on this.
> Truly there is no specific statement about whether micro-TLB support 16MB
> super-sections,
> but main-TLB actually helps the hit rate, and main-TLB support all page size
> mapping.

The feedback over time was that 16MB didn't help much in terms of TLB
misses compared to 1MB but that was for standard usage. I guess the
hugetlbfs has specific scenarios that may benefit.

Anyway, could you make the 2MB/16MB huge page size configurable at
boot time (command line option like on other architectures)? And also
check the ID_MMFR0[31:28] for whether supersections are supported.

>> BTW, I have a (simpler) implementation of hugetlbfs with 2MB sections
>> but for LPAE only:
>>
>>
>> http://git.kernel.org/?p=linux/kernel/git/cmarinas/linux-arm-arch.git;a=shortlog;h=refs/heads/hugetlb
>>
> Thanks for your information, I will study your code carefully :)

Most of the simplicity comes from the fact that LPAE doesn't need a
separate Linux PTE table.

-- 
Catalin