On Tue 09-10-18 14:00:34, Mel Gorman wrote:
On Tue, Oct 09, 2018 at 02:27:45PM +0200, Michal Hocko wrote:
[Sorry for being slow in responding but I was mostly offline last few days]
On Tue 09-10-18 10:48:25, Mel Gorman wrote: [...]
This goes back to my point that the MADV_HUGEPAGE hint should not make promises about locality and that introducing MADV_LOCAL for specialised libraries may be more appropriate with the initial semantic being how it treats MADV_HUGEPAGE regions.
I agree with your other points and not going to repeat them. I am not sure madvise s the best API for the purpose though. We are talking about memory policy here and there is an existing api for that so I would _prefer_ to reuse it for this purpose.
I flip-flopped on that one in my head multiple times on the basis of how strict it should be. Memory policies tend to be black or white -- bind here, interleave there, etc. It wasn't clear to me what the best policy would be to describe "allocate local as best as you can but allow fallbacks if necessary".
I was thinking about MPOL_NODE_PROXIMITY with the following semantic: - try hard to allocate from a local or very close numa node(s) even when that requires expensive operations like the memory reclaim/compaction before falling back to other more distant numa nodes.
Hence, I started leaning towards advise as it is really about advice that the kernel can ignore if necessary. That said, I don't feel as strongly about the "how" as I do about the fact that applications and libraries should not depend on side-effects of the MADV_HUGEPAGE implementation that relate to locality.
completely agreed on this.