On 21/06/2024 08:47, Barry Song wrote: > On Fri, Jun 21, 2024 at 7:25 PM Ryan Roberts <ryan.roberts@xxxxxxx> wrote: >> >> On 20/06/2024 12:34, David Hildenbrand wrote: >>> On 20.06.24 11:04, Ryan Roberts wrote: >>>> On 20/06/2024 01:26, Barry Song wrote: >>>>> From: Barry Song <v-songbaohua@xxxxxxxx> >>>>> >>>>> Both Ryan and Chris have been utilizing the small test program to aid >>>>> in debugging and identifying issues with swap entry allocation. While >>>>> a real or intricate workload might be more suitable for assessing the >>>>> correctness and effectiveness of the swap allocation policy, a small >>>>> test program presents a simpler means of understanding the problem and >>>>> initially verifying the improvements being made. >>>>> >>>>> Let's endeavor to integrate it into the self-test suite. Although it >>>>> presently only accommodates 64KB and 4KB, I'm optimistic that we can >>>>> expand its capabilities to support multiple sizes and simulate more >>>>> complex systems in the future as required. >>>> >>>> I'll try to summarize the thread with Huang Ying by suggesting this test program >>>> is "neccessary but not sufficient" to exhaustively test the mTHP swap-out path. >>>> I've certainly found it useful and think it would be a valuable addition to the >>>> tree. >>>> >>>> That said, I'm not convinced it is a selftest; IMO a selftest should provide a >>>> clear pass/fail result against some criteria and must be able to be run >>>> automatically by (e.g.) a CI system. >>> >>> Likely we should then consider moving other such performance-related thingies >>> out of the selftests? >> >> Yes, that would get my vote. But of the 4 tests you mentioned that use >> clock_gettime(), it looks like transhuge-stress is the only one that doesn't >> have a pass/fail result, so is probably the only candidate for moving. >> >> The others either use the times as a timeout and determines failure if the >> action didn't occur within the timeout (e.g. ksm_tests.c) or use it to add some >> supplemental performance information to an otherwise functionality-oriented test. > > Thank you very much, Ryan. I think you've found a better home for this > tool . I will > send v2, relocating it to tools/mm and adding a function to swap in > either the whole > mTHPs or a portion of mTHPs by "-a"(aligned swapin). > > So basically, we will have > > 1. Use MADV_PAGEPUT for rapid swap-out, putting the swap allocation code under > high exercise in a short time. > > 2. Use MADV_DONTNEED to simulate the behavior of libc and Java heap in freeing > memory, as well as for munmap, app exits, or OOM killer scenarios. This ensures > new mTHP is always generated, released or swapped out, similar to the behavior > on a PC or Android phone where many applications are frequently started and > terminated. > > 3. Swap in with or without the "-a" option to observe how fragments > due to swap-in > and the incoming swap-in of large folios will impact swap-out fallback. > > And many thanks to Chris for the suggestion on improving it within > selftest, though I > prefer to place it in tools/mm. All sounds good to me! If, (for future) you also wanted to test the vmscan swap-out path, the way I've been doing that is to run the workload in a memory-constrained cgroup. That means you don't need to exhaust all your phsical ram so speeds things up a lot. > > Thanks > Barry
