Re: [PATCH 0/2] fix for "pathological THP behavior"

On Tue, 21 Aug 2018, Vlastimil Babka wrote:

Frankly, I would rather go with this option and assume that if someone
explicitly wants THP's, they don't care about NUMA locality that much.
(Note: I hate __GFP_THISNODE, it's an endless source of issues.)
Trying to be clever about "is there still PAGE_SIZEd free memory in the
local node" is imperfect anyway. If there isn't, is it because there's
clean page cache that we can easily reclaim (so it would be worth
staying local) or is it really exhausted? Watermark check won't tell...

MADV_HUGEPAGE (or defrag == "always") would now become a combination of 
"try to compact locally" and "allocate remotely if necesary" without the 
ability to avoid the latter absent a mempolicy that affects all memory 
allocations.  I think the complete solution would be a MPOL_F_HUGEPAGE 
flag that defines mempolicies for hugepage allocations.  In my experience 
thp falling back to remote nodes for intrasocket latency is a win but 
intersocket or two-hop intersocket latency is a no go.