On Mon, Aug 20, 2018 at 4:58 AM, Kirill A. Shutemov <kirill@xxxxxxxxxxxxx> wrote: > On Sun, Aug 19, 2018 at 11:22:02PM -0400, Andrea Arcangeli wrote: >> Hello, >> >> we detected a regression compared to older kernels, only happening >> with defrag=always or by using MADV_HUGEPAGE (and QEMU uses it). >> >> I haven't bisected but I suppose this started since commit >> 5265047ac30191ea24b16503165000c225f54feb combined with previous >> commits that introduced the logic to not try to invoke reclaim for THP >> allocations in the remote nodes. >> >> Once I looked into it the problem was pretty obvious and there are two >> possible simple fixes, one is not to invoke reclaim and stick to >> compaction in the local node only (still __GFP_THISNODE model). >> >> This approach keeps the logic the same and prioritizes for NUMA >> locality over THP generation. >> >> Then I'll send the an alternative that drops the __GFP_THISNODE logic >> if_DIRECT_RECLAIM is set. That however changes the behavior for >> MADV_HUGEPAGE and prioritizes THP generation over NUMA locality. >> >> A possible incremental improvement for this __GFP_COMPACT_ONLY >> solution would be to remove __GFP_THISNODE (and in turn >> __GFP_COMPACT_ONLY) after checking the watermarks if there's no free >> PAGE_SIZEd memory in the local node. However checking the watermarks >> in mempolicy.c is not ideal so it would be a more messy change and >> it'd still need to use __GFP_COMPACT_ONLY as implemented here for when >> there's no PAGE_SIZEd free memory in the local node. That further >> improvement wouldn't be necessary if there's agreement to prioritize >> THP generation over NUMA locality (the alternative solution I'll send >> in a separate post). > > I personally prefer to prioritize NUMA locality over THP > (__GFP_COMPACT_ONLY variant), but I don't know page-alloc/compaction good > enough to Ack it. May the approach #1 break the setting of zone_reclaim_mode? Or it may behave like zone_reclaim_mode is set even though the knob is cleared? Thanks, Yang > > -- > Kirill A. Shutemov >
