On Fri, Apr 12, 2024 at 11:27:04AM +0800, Baolin Wang wrote: > Currently, compaction_capture() does not allow lower-order allocations to > directly capture the movable free pages, even though lower-order allocations > might also be requesting movable pages, that can lead to more compaction > scanning. And, with the enablement of mTHP, such situations will become more > common. > > Thus allowing lower-order (mTHP) allocations of movable page types directly > capture the movable free pages can avoid unnecessary compaction scanning, > meanwhile that won't pollute the movable pageblock. With testing 1M mTHP > compaction, it can be seen that compaction scanning is significantly reduced. > > mm-unstable patched > Ops Compaction pages isolated 116598741.00 120946702.00 > Ops Compaction migrate scanned 1764870054.00 1488621550.00 > Ops Compaction free scanned 7707879039.00 4986299318.00 > Ops Compact scan efficiency 22.90 29.85 > Ops Compaction cost 73797.69 72933.48 > > Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx> Letting a movable request into a partially compacted movable block seems reasonable. The only advantage of not doing so that I could imagine would be to avoid mixing old with new pages, such that reclaim is more likely to free blocks due to improved LRU grouping. But that seems far-fetched. Notably, __compact_finished() will also stop once the requested MOVABLE order becomes available; so not capturing at that point likely just results in stolen work and compaction restarts. Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
