Performance issue

[zhongyuansh]

Hi,

Maybe I found a performance issue of XPMEM.

1. xpmem_attach use the function "remap_pfn_range" to map page to vma.
2. But this funtion will split 2M huge page to 4KB page
3. 4KB TLB miss will increase, this is a performance issue

Is there any way to fix this issue?

[hjelmn]

Not sure. I haven't looked at the implementation of remap_pfn_range to see if it will cause this to happen. If it does, I expect that Cray probably modified their kernel to not split the pages. If huge pages are indeed being split I welcome a fix if someone has one. I probably won't find time to work on this myself anytime soon.

[deantroe]

It does result in 4kb pages, and Cray does not have any magic to make them remain huge pages. That would be ideal, but last I looked there was no logical path to do that.