Messages in this thread | | | Date | Thu, 19 Oct 2023 16:51:08 +0800 | Subject | Re: [PATCH] mm: migrate: record the mlocked page status to remove unnecessary lru drain | From | Baolin Wang <> |
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On 10/19/2023 4:22 PM, Yin Fengwei wrote: > Hi Baolin, > > On 10/19/23 15:25, Baolin Wang wrote: >> >> >> On 10/19/2023 2:09 PM, Huang, Ying wrote: >>> Zi Yan <ziy@nvidia.com> writes: >>> >>>> On 18 Oct 2023, at 9:04, Baolin Wang wrote: >>>> >>>>> When doing compaction, I found the lru_add_drain() is an obvious hotspot >>>>> when migrating pages. 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().
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