Re: [PATCH -V2 -mm] mm, hugetlbfs: Pass fault address to no page handler

["Huang\, Ying" <ying.huang@intel.com>]

Mike Kravetz <mike.kravetz@oracle.com> writes:

> On 05/17/2018 01:35 AM, Huang, Ying wrote:
>> From: Huang Ying <ying.huang@intel.com>
>> 
>> This is to take better advantage of general huge page clearing
>> optimization (c79b57e462b5d, "mm: hugetlb: clear target sub-page last
>> when clearing huge page") for hugetlbfs.  In the general optimization
>> patch, the sub-page to access will be cleared last to avoid the cache
>> lines of to access sub-page to be evicted when clearing other
>> sub-pages.  This works better if we have the address of the sub-page
>> to access, that is, the fault address inside the huge page.  So the
>> hugetlbfs no page fault handler is changed to pass that information.
>> This will benefit workloads which don't access the begin of the
>> hugetlbfs huge page after the page fault under heavy cache contention
>> for shared last level cache.
>> 
>> The patch is a generic optimization which should benefit quite some
>> workloads, not for a specific use case.  To demonstrate the performance
>> benefit of the patch, we tested it with vm-scalability run on
>> hugetlbfs.
>> 
>> With this patch, the throughput increases ~28.1% in vm-scalability
>> anon-w-seq test case with 88 processes on a 2 socket Xeon E5 2699 v4
>> system (44 cores, 88 threads).  The test case creates 88 processes,
>> each process mmaps a big anonymous memory area with MAP_HUGETLB and
>> writes to it from the end to the begin.  For each process, other
>> processes could be seen as other workload which generates heavy cache
>> pressure.  At the same time, the cache miss rate reduced from ~36.3%
>> to ~25.6%, the IPC (instruction per cycle) increased from 0.3 to 0.37,
>> and the time spent in user space is reduced ~19.3%.
>> 
>
> Agree with Michal that commit message looks better.
>
> I went through updated patch with haddr naming so,
> Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
> still applies.

Thanks!

Best Regards,
Huang, Ying