The big change here is that I dropped the patch that batches TLB flushes from migration context. After V3, I realised that there are non-trivial corner cases there that deserve treatment in their own series. It did not help that I could not find a workload that was both migration and IPI intensive. The common case for IPIs during reclaim is kswapd unmapping pages which guarantees IPIs. In migration, at least some of the pages being migrated will belong to the process itself. The main issue is that migration cannot have any cached TLB entries after migration completes. Once the migration PTE is removed then writes can happen to that new page. The old TLB entry could see stale reads until it's flushed which is different to the reclaim case. This is difficult to get around. We cannot just unmap in advance because then there are no migration entries to restore and there would be minor faults post-migration. We can't batch restore the migration entries because the page lock must be held during migration or BUG_ONs get triggered. Batching TLB flushes safely requires a major rethink of how migration works so lets deal with reclaim first on its own, preferably in the context of a workload that is both migration and IPI intensive. The patch that increased the batching size was also removed because there is no advantage when TLBs are flushed before freeing the page. To increase batching we would have to alter how many pages are isolated from the LRU which would be a different patch series. Most reviewed-bys had to be dropped as the patches changed too much to preserve them. Changelog since V3 o Drop batching of TLB flush from migration o Redo how larger batching is managed o Batch TLB flushes when writable entries exist When unmapping pages it is necessary to flush the TLB. If that page was accessed by another CPU then an IPI is used to flush the remote CPU. That is a lot of IPIs if kswapd is scanning and unmapping >100K pages per second. There already is a window between when a page is unmapped and when it is TLB flushed. This series simply increases the window so multiple pages can be flushed using a single IPI. Patch 1 simply made the rest of the series easier to write as ftrace could identify all the senders of TLB flush IPIS. Patch 2 collects a list of PFNs and sends one IPI to flush them all Patch 3 tracks when there potentially are writable TLB entries that need to be batched differently The performance impact is documented in the changelogs but in the optimistic case on a 4-socket machine the full series reduces interrupts from 900K interrupts/second to 60K interrupts/second. arch/x86/Kconfig | 1 + arch/x86/include/asm/tlbflush.h | 2 + arch/x86/mm/tlb.c | 1 + include/linux/init_task.h | 8 +++ include/linux/mm_types.h | 1 + include/linux/rmap.h | 3 + include/linux/sched.h | 15 +++++ include/trace/events/tlb.h | 3 +- init/Kconfig | 8 +++ kernel/fork.c | 5 ++ kernel/sched/core.c | 3 + mm/internal.h | 15 +++++ mm/rmap.c | 119 +++++++++++++++++++++++++++++++++++++++- mm/vmscan.c | 45 ++++++++++++++- 14 files changed, 224 insertions(+), 5 deletions(-) -- 2.3.5 Mel Gorman (3): x86, mm: Trace when an IPI is about to be sent mm: Send one IPI per CPU to TLB flush multiple pages that were recently unmapped mm: Defer flush of writable TLB entries arch/x86/Kconfig | 1 + arch/x86/include/asm/tlbflush.h | 2 + arch/x86/mm/tlb.c | 1 + include/linux/init_task.h | 8 +++ include/linux/mm_types.h | 1 + include/linux/rmap.h | 3 + include/linux/sched.h | 15 +++++ include/trace/events/tlb.h | 3 +- init/Kconfig | 8 +++ kernel/fork.c | 5 ++ kernel/sched/core.c | 3 + mm/internal.h | 15 +++++ mm/rmap.c | 119 +++++++++++++++++++++++++++++++++++++++- mm/vmscan.c | 30 +++++++++- 14 files changed, 210 insertions(+), 4 deletions(-) -- 2.3.5 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>