Re: [LSF/MM TOPIC] NUMA remote THP vs NUMA local non-THP under MADV_HUGEPAGE

[Mike Kravetz]

On 1/29/19 3:40 PM, Andrea Arcangeli wrote:
> In addition to the above "NUMA remote THP vs NUMA local non-THP
> tradeoff" topic, there are other developments in "userfaultfd" land that
> are approaching merge readiness and that would be possible to provide a
> short overview about:
> 
> - Peter Xu made significant progress in finalizing the userfaultfd-WP
>   support over the last few months. That feature was planned from the
>   start and it will allow userland to do some new things that weren't
>   possible to achieve before. In addition to synchronously blocking
>   write faults to be resolved by an userland manager, it has also the
>   ability to obsolete the softdirty feature, because it can provide
>   the same information, but with O(1) complexity (as opposed of the
>   current softdirty O(N) complexity) similarly to what the Page
>   Modification Logging (PML) does in hardware for EPT write accesses.

I would be interested in this topic as well.  IIRC, Peter's patches do
not address hugetlbfs support.  I put together patches for this some
time back.  At the time, they worked as well as userfaultfd-WP support
for normal base pages: not too well :).  Once base page support is
finalized, I suspect I will be involved in hugetlbfs support.

-- 
Mike Kravetz