Re: ksm: add mremap selftests for ksm_rmap_walk

[David Hildenbrand (Arm)]

> 
> Oh, thanks to David and Hugh's reminder, I now understand the issue Hugh was pointing out, and I also
> see why my current test program incorrectly passes: before migrating the memory page, the
> mremap() operation has already turned a KSM page into an anonymous page, causing the code to
> take rmap_walk_anon instead of rmap_walk_ksm. Therefore, to reproduce the issue Hugh described,
> we only need to add a delay of wait_ksmd_scan_finish_two_truns before migration (after mremap) 
> 
> 	— simply wait for ksmd to merge the remapped page back into a KSM page.
> 
> such testing code can reproduce what Hugh points out and FAIL to migrate:
>
Cool, please update the test to take that into account, and please also
test with child processes involved (no mremap() in child, only mremap()
before merging in the host).

-- 
Cheers,

David