[Question] What does "Huge Page Allocation Ratio" mean in Section 6.2 about amp HOT 4 CLOSED

Dear Yaland.

Thank you for having an interest in our work.

We enabled transparent huge pages (THP) of the Linux kernel to use huge pages.
THP does not guarantee huge page allocation, and the kernel may return 4KB base pages if it fails to find physically contiguous 2MB-aligned free memory.

The huge page allocation ratio presents how much of allocated memory is backed by huge pages.
It is defined as (allocated memory size backed by 2MB huge pages / allocated memory size) * 100.

from amp.

Hello Dr.Heo,

Thanks for your explanation!

I still have another question about this section. In Figure 10, you compare the performace between "modified LRU list" and "LRU". What's the difference between them? What does "LRU" refer to? Does it mean Linux's active/inactive list or "real" LRU policy (i.e. track every memory access and move list nodes accordingly) ?

from amp.

The modified LRU lists refer to the prior study that I have mentioned in Section 3.3.
(Nimble Page Management for Tiered Memory Systems, https://dl.acm.org/doi/10.1145/3297858.3304024)

LRU, LFU, and Random are the migration policies that I have described at the end of Section 3.1. LRU in the legend is different from the native Linux's active / inactive lists.

from amp.

Ok. Thanks!

from amp.