On 2020-01-20 at 17:51 Anshuman Khandual wrote: > > >On 01/16/2020 08:48 PM, Michal Hocko wrote: >> On Thu 16-01-20 21:50:34, Li Xinhai wrote: >>> On 2020-01-16 at 17:56 Michal Hocko wrote: >>>> On Thu 16-01-20 04:11:25, Li Xinhai wrote: >>>>> Checking hstate at early phase when isolating page, instead of during >>>>> unmap and move phase, to avoid useless isolation. >>>> >>>> Could you be more specific what you mean by isolation and why does it >>>> matter? The patch description should really explain _why_ the change is >>>> needed or desirable. >>> >>> The changelog can be improved: >>> >>> vma_migratable() is called to check if pages in vma can be migrated >>> before go ahead to isolate, unmap and move pages. For hugetlb pages, >>> hugepage_migration_supported(struct hstate *h) is one factor which >>> decide if migration is supported. In current code, this function is called >>> from unmap_and_move_huge_page(), after isolating page has >>> completed. >>> This patch checks hstate from vma_migratable() and avoids isolating pages >>> which are not supported. >> >> This still explains what but not why this is relevant. If by isolating >> pages you mean isolate_lru_page then this really a noop for hugetlb >> pages. Or do I still misread your changelog? > >unmap_and_move_hugepage() aborts migrating a HugeTLB page (from the list) >if it's corresponding hstate does not support migration. IIUC the current >proposal will enable early bail out and prevent migration via migrate_pages() >at a much higher level like mbind() and other system calls if corresponding >VMA is HugeTLB but it's hstate lacks migration support. This should probably >save some cycles for HugeTLB VMAs. Thanks for comments. Yes，this patch is for enable early bail out.
