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The distribution of this hotspot is as follows: >>>>>>>>>>        - 18.75% compact_zone >>>>>>>>>>           - 17.39% migrate_pages >>>>>>>>>>              - 13.79% migrate_pages_batch >>>>>>>>>>                 - 11.66% migrate_folio_move >>>>>>>>>>                    - 7.02% lru_add_drain >>>>>>>>>>                       + 7.02% lru_add_drain_cpu >>>>>>>>>>                    + 3.00% move_to_new_folio >>>>>>>>>>                      1.23% rmap_walk >>>>>>>>>>                 + 1.92% migrate_folio_unmap >>>>>>>>>>              + 3.20% migrate_pages_sync >>>>>>>>>>           + 0.90% isolate_migratepages >>>>>>>>>> >>>>>>>>>> The lru_add_drain() was added by commit c3096e6782b7 ("mm/migrate: >>>>>>>>>> __unmap_and_move() push good newpage to LRU") to drain the newpage to LRU >>>>>>>>>> immediately, to help to build up the correct newpage->mlock_count in >>>>>>>>>> remove_migration_ptes() for mlocked pages. However, if there are no mlocked >>>>>>>>>> pages are migrating, then we can avoid this lru drain operation, especailly >>>>>>>>>> for the heavy concurrent scenarios. >>>>>>>>> >>>>>>>>> lru_add_drain() is also used to drain pages out of folio_batch. Pages in folio_batch >>>>>>>>> have an additional pin to prevent migration. See folio_get(folio); in folio_add_lru(). >>>>>>>> >>>>>>>> lru_add_drain() is called after the page reference count checking in >>>>>>>> move_to_new_folio().  So, I don't this is an issue. >>>>>>> >>>>>>> Agree. The purpose of adding lru_add_drain() is to address the 'mlock_count' issue for mlocked pages. Please see commit c3096e6782b7 and related comments. Moreover I haven't seen an increase in the number of page migration failures due to page reference count checking after this patch. >>>>>> >>>>>> I agree with your. My understanding also is that the lru_add_drain() is only needed >>>>>> for mlocked folio to correct mlock_count. Like to hear the confirmation from Huge. >>>>>> >>>>>> >>>>>> But I have question: why do we need use page_was_mlocked instead of check >>>>>> folio_test_mlocked(src)? Does page migration clear the mlock flag? Thanks. >>>>> >>>>> Yes, please see the call trace: try_to_migrate_one() ---> page_remove_rmap() ---> munlock_vma_folio(). >>>> >>>> Yes. This will clear mlock bit. >>>> >>>> What about set dst folio mlocked if source is before try_to_migrate_one()? And >>>> then check whether dst folio is mlocked after? And need clear mlocked if migration >>>> fails. I suppose the change is minor. Just a thought. Thanks. >>> >>> IMO, this will break the mlock related statistics in mlock_folio() when the remove_migration_pte() rebuilds the mlock status and mlock count. >>> >>> Another concern I can see is that, during the page migration, a concurrent munlock() can be called to clean the VM_LOCKED flags for the VMAs, so the remove_migration_pte() should not rebuild the mlock status and mlock count. But the dst folio's mlcoked status is still remained, which is wrong. >>> >>> So your suggested apporach seems not easy, and I think my patch is simple with re-using existing __migrate_folio_record() and __migrate_folio_extract() :) >> >> Can these concerns be addressed by clear dst mlocked after lru_add_drain() but before >> remove_migration_pte()? > > IMHO, that seems too hacky to me. I still prefer to rely on the migration process of the mlcock pages. Fair enough. Thanks. Regards Yin, Fengwei