On 09/26/2014 10:03 AM, Steve Capper wrote:

This series implements general forms of get_user_pages_fast and
__get_user_pages_fast in core code and activates them for arm and arm64.

These are required for Transparent HugePages to function correctly, as
a futex on a THP tail will otherwise result in an infinite loop (due to
the core implementation of __get_user_pages_fast always returning 0).

Unfortunately, a futex on THP tail can be quite common for certain
workloads; thus THP is unreliable without a __get_user_pages_fast
implementation.

This series may also be beneficial for direct-IO heavy workloads and
certain KVM workloads.

I appreciate that the merge window is coming very soon, and am posting
this revision on the off-chance that it gets the nod for 3.18. (The changes
thus far have been minimal and the feedback I've got has been mainly
positive).

Head's up: these patches are currently implicated in a rare-to-trigger
hang that we are seeing on an internal kernel. An extensive effort is
underway to confirm whether these are the cause. Will followup.

Jon.