Hi Tim, On Tue, Sep 13, 2016 at 11:52:27PM +0000, Chen, Tim C wrote: > >> > >> - Avoid CPU time for splitting, collapsing THP across swap out/in. > > > >Yes, if you want, please give us how bad it is. > > > > It could be pretty bad. In an experiment with THP turned on and we > enter swap, 50% of the cpu are spent in the page compaction path.
It's page compaction overhead, especially, pageblock_pfn_to_page. Why is it related to overhead THP split for swapout? I don't understand. > So if we could deal with units of large page for swap, the splitting > and compaction of ordinary pages to large page overhead could be avoided. > > 51.89% 51.89% :1688 [kernel.kallsyms] [k] > pageblock_pfn_to_page > | > --- pageblock_pfn_to_page > | > |--64.57%-- compaction_alloc > | migrate_pages > | compact_zone > | compact_zone_order > | try_to_compact_pages > | __alloc_pages_direct_compact > | __alloc_pages_nodemask > | alloc_pages_vma > | do_huge_pmd_anonymous_page > | handle_mm_fault > | __do_page_fault > | do_page_fault > | page_fault > | 0x401d9a > | > |--34.62%-- compact_zone > | compact_zone_order > | try_to_compact_pages > | __alloc_pages_direct_compact > | __alloc_pages_nodemask > | alloc_pages_vma > | do_huge_pmd_anonymous_page > | handle_mm_fault > | __do_page_fault > | do_page_fault > | page_fault > | 0x401d9a > --0.81%-- [...] > > Tim
