On 01/20/2020 09:35 PM, Michal Hocko wrote: > On Mon 20-01-20 23:37:25, Li Xinhai wrote: > [...] >> Changelog is updated as below, thanks for comments: >> --- >> mm/mempolicy: Checking hugepage migration is supported by arch in vma_migratable >> >> vma_migratable() is called to check if pages in vma can be migrated >> before go ahead to further actions. Currently it is used in below code >> path: >> - task_numa_work >> - mbind >> - move_pages >> >> For hugetlb mapping, whether vma is migratable or not is determined by: >> - CONFIG_ARCH_ENABLE_HUGEPAGE_MIGRATION >> - arch_hugetlb_migration_supported >> >> Issue: current code only checks for CONFIG_ARCH_ENABLE_HUGEPAGE_MIGRATION, >> which express less accurate semantics of vma_migratable(). (note that >> current code in vma_migratable don't cause failure or bug because >> unmap_and_move_huge_page() will catch unsupported hugepage and handle it >> properly) >> >> This patch checks the two factors for impoveing code logic and >> robustness. It will enable early bail out of hugepage migration procedure, >> but because currently all architecture supporting hugepage migration is able >> to support all page size, we would not see performance gain with this patch >> applied. > > This looks definitely better than the original one. I hope it is more > clear to you what I meant by a better description for the justification. > I would just add that the no code should use > CONFIG_ARCH_ENABLE_HUGEPAGE_MIGRATION directly and use > arch_hugetlb_migration_supported instead. This will be the case after > this patch. As I have mentioned previously on the other thread, there might be an case to keep the existing code (just added with a comment) which will preserve the performance. But the proposed method will do it the right way and also get rid of CONFIG_ARCH_ENABLE_HUGEPAGE_MIGRATION here. Its OK either way. > > Please keep in mind that changelogs are really important and growing in > importance as the code gets more complicated over time. It is much more > easier to see what the patch does because reading diffs and the code is > easy but the lack of motivation is what people usually fighting with. >
