On 20/10/2023 13:33, Ryan Roberts wrote: > On 06/10/2023 21:06, David Hildenbrand wrote: >> On 29.09.23 13:44, Ryan Roberts wrote: >>> Hi All, >> > > [...] > >>> NOTE: These changes should not be merged until the prerequisites are complete. >>> These are in progress and tracked at [7]. >> >> We should probably list them here, and classify which one we see as strict a >> requirement, which ones might be an optimization. >> > > Bringing back the discussion of prerequistes to this thread following the > discussion at the mm-alignment meeting on Wednesday. > > Slides, updated following discussion to reflect all the agreed items that are > prerequisites and enhancements, are at [1]. > > I've taken a closer look at the situation with khugepaged, and can confirm that > it does correctly collapse anon small-sized THP into PMD-sized THP. I did notice > though, that one of the khugepaged selftests (collapse_max_ptes_none) fails when > small-sized THP is enabled+always. So I've fixed that test up and will add the > patch to the next version of my series. > > So I believe the khugepaged prerequisite can be marked as done. > > [1] > https://drive.google.com/file/d/1GnfYFpr7_c1kA41liRUW5YtCb8Cj18Ud/view?usp=sharing&resourcekey=0-U1Mj3-RhLD1JV6EThpyPyA Hi All, It's been a week since the mm alignment meeting discussion we had around prerequisites and the ABI. I haven't heard any further feedback on the ABI proposal, so I'm going to be optimistic and assume that nobody has found any fatal flaws in it :). Certainly, I think it held up to the potential future policies that Yu Zhou cited on the call - the possibility of preferring a smaller size over a bigger one, if the smaller size can be allocated without splitting a contiguous block. I think the suggestion of adding a per-size priority file would solve it. And in general because we have a per-size directory, that gives us lots of flexibility for growth. Anyway, given the lack of feedback, I'm proposing to spin a new version. I'm planning to do the following: - Drop the accounting patch (#3); we will continue to only account PMD-sized THP for now. We can add more counters in future if needed. page cache large folios haven't needed any new counters yet. - Pivot to the ABI proposed by DavidH; per-size directories in a similar shape to that used by hugetlb - Drop the "recommend" keyword patch (#6); For now, users will need to understand implicitly which sizes are beneficial to their HW perf - Drop patch (#7); arch_wants_pte_order() is no longer needed due to dropping patch #6 - Add patch for khugepaged selftest improvement (described in previous email above). - Ensure that PMD_ORDER is not assumed to be compile-time constant (current code is broken on powerpc) Please shout if you think this is the wrong approach. On the prerequisites front, we have 2 items still to land: - compaction; Zi Yan is working on a v2 - numa balancing; A developer has signed up and is working on it (I'll leave them to reveal themself as preferred). Thanks, Ryan
