[RFC PATCH V3 3/6] arm: mm: implement get_user_pages_fast

[Steve Capper]

On 12 March 2014 17:15, Catalin Marinas <catalin.marinas at arm.com> wrote:
> On Wed, Mar 12, 2014 at 01:40:20PM +0000, Steve Capper wrote:
>> An implementation of get_user_pages_fast for ARM. It is based loosely
>> on the PowerPC implementation. We disable interrupts in the walker to
>> prevent the call_rcu_sched pagetable freeing code from running under
>> us.
>>
>> We also explicitly fire an IPI in the Transparent HugePage splitting
>> case to prevent splits from interfering with the fast_gup walker.
>> As THP splits are relatively rare, this should not have a noticable
>> overhead.
>>
>> Signed-off-by: Steve Capper <steve.capper at linaro.org>
>> ---
>>  arch/arm/include/asm/pgtable-3level.h |   6 +
>>  arch/arm/mm/Makefile                  |   1 +
>>  arch/arm/mm/gup.c                     | 299 ++++++++++++++++++++++++++++++++++
>>  3 files changed, 306 insertions(+)
>>  create mode 100644 arch/arm/mm/gup.c
>
> Is there anything specific to ARM in this gup.c file? Could we make it
> more generic like mm/gup.c?

Hi Catalin,
The arm and arm64 cases assume that we can read the pte's atomically,
that TLB hardware broadcasts can occur (so we have to use the
page_cache_get_speculative logic), and that hugetlb pages are
equivalent in pte layout to thp's.

Also, I took a quick look at the other architectures, and a summary of
what I found can be found in this post:
http://lists.infradead.org/pipermail/linux-arm-kernel/2014-March/239326.html

Cheers,
-- 
Steve

>
> --
> Catalin