Messages in this thread | | | Date | Sat, 21 Oct 2023 11:31:20 +0800 | Subject | Re: [PATCH v2] mm: migrate: record the mlocked page status to remove unnecessary lru drain | From | Baolin Wang <> |
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On 10/20/2023 12:48 PM, Hugh Dickins wrote: > On Fri, 20 Oct 2023, 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. >> >> So we can record the source pages' mlocked status in migrate_folio_unmap(), >> and only drain the lru list when the mlocked status is set in migrate_folio_move(). >> In addition, the page was already isolated from lru when migrating, so checking >> the mlocked status is stable by folio_test_mlocked() in migrate_folio_unmap(). >> >> After this patch, I can see the hotpot of the lru_add_drain() is gone: >> - 9.41% migrate_pages_batch >> - 6.15% migrate_folio_move >> - 3.64% move_to_new_folio >> + 1.80% migrate_folio_extra >> + 1.70% buffer_migrate_folio >> + 1.41% rmap_walk >> + 0.62% folio_add_lru >> + 3.07% migrate_folio_unmap >> >> Meanwhile, the compaction latency shows some improvements when running >> thpscale: >> base patched >> Amean fault-both-1 1131.22 ( 0.00%) 1112.55 * 1.65%* >> Amean fault-both-3 2489.75 ( 0.00%) 2324.15 * 6.65%* >> Amean fault-both-5 3257.37 ( 0.00%) 3183.18 * 2.28%* >> Amean fault-both-7 4257.99 ( 0.00%) 4079.04 * 4.20%* >> Amean fault-both-12 6614.02 ( 0.00%) 6075.60 * 8.14%* >> Amean fault-both-18 10607.78 ( 0.00%) 8978.86 * 15.36%* >> Amean fault-both-24 14911.65 ( 0.00%) 11619.55 * 22.08%* >> Amean fault-both-30 14954.67 ( 0.00%) 14925.66 * 0.19%* >> Amean fault-both-32 16654.87 ( 0.00%) 15580.31 * 6.45%* >> > > Seems a sensible change with good results (I'll conceal how little of > the stats I understand, I expect everyone else understands them: in my > naivety, I'm mainly curious why rmap_walk's 1.23% didn't get a + on it).
TBH, I also don't know why the rmap_walk didn't get a + on it, let me check it again.
>> Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com> >> --- >> Chages from v1: >> - Use separate flags in __migrate_folio_record() to avoid to pack flags >> in each call site per Ying. >> --- >> mm/migrate.c | 47 +++++++++++++++++++++++++++++++++++------------ >> 1 file changed, 35 insertions(+), 12 deletions(-) >> >> diff --git a/mm/migrate.c b/mm/migrate.c >> index 125194f5af0f..fac96139dbba 100644 >> --- a/mm/migrate.c >> +++ b/mm/migrate.c >> @@ -1027,22 +1027,39 @@ union migration_ptr { >> struct anon_vma *anon_vma; >> struct address_space *mapping; >> }; >> + >> +enum { >> + PAGE_WAS_MAPPED = 1 << 0, >> + PAGE_WAS_MLOCKED = 1 << 1, >> +}; >> + > > I was whispering to myself "I bet someone will suggest BIT()"; > and indeed that someone has turned out to be Huang, Ying.
Sure.
> >> static void __migrate_folio_record(struct folio *dst, >> - unsigned long page_was_mapped, >> + unsigned int page_was_mapped, >> + unsigned int page_was_mlocked, >> struct anon_vma *anon_vma) >> { >> union migration_ptr ptr = { .anon_vma = anon_vma }; >> + unsigned long page_flags = 0; > > Huang, Ying preferred a different name, me too: old_page_state?
OK, sounds better to me.
> >> + >> + if (page_was_mapped) >> + page_flags |= PAGE_WAS_MAPPED; >> + if (page_was_mlocked) >> + page_flags |= PAGE_WAS_MLOCKED; > > What's annoying me about the patch is all this mix of page_was_mapped and > page_was_mlocked variables, then the old_page_state bits. Can't it be > done with PAGE_WAS_ bits in old_page_state throughout, without any > page_was_mapped and page_was_mlocked variables?
Yes, good point. Let me try it. Thanks for your comments.
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