Re: [PATCH -mm] mm, huge page: Copy to access sub-page last when copy huge page

[Mike Kravetz]

On 05/17/2018 11:24 PM, Michal Hocko wrote:
> On Fri 18-05-18 11:03:16, Huang, Ying wrote:
> [...]
>> 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
>> transparent huge page.
> 
> It is also adds quite some non-intuitive code. So is this worth? Does
> any _real_ workload benefits from the change?

One way to 'add less code' would be to create a helper routine that
indicates the order in which sub-pages are to be copied.  IIUC, you
added the same algorithm for sub-page ordering to copy_huge_page()
that was previously added to clear_huge_page().  Correct?  If so,
then perhaps a common helper could be used by both the clear and copy
huge page routines.  It would also make maintenance easier.

-- 
Mike Kravetz