In many cases, if collect_longterm_unpinnable_folios() does need to drain the LRU cache to release a reference, the cache in question is on this same CPU, and much more efficiently drained by a preliminary local lru_add_drain(), than the later cross-CPU lru_add_drain_all(). Marked for stable, to counter the increase in lru_add_drain_all()s from "mm/gup: check ref_count instead of lru before migration". Note for clean backports: can take 6.16 commit a03db236aebf ("gup: optimize longterm pin_user_pages() for large folio") first. Signed-off-by: Hugh Dickins Cc: --- mm/gup.c | 15 +++++++++++---- 1 file changed, 11 insertions(+), 4 deletions(-) diff --git a/mm/gup.c b/mm/gup.c index 82aec6443c0a..b47066a54f52 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -2287,8 +2287,8 @@ static unsigned long collect_longterm_unpinnable_folios( struct pages_or_folios *pofs) { unsigned long collected = 0; - bool drain_allow = true; struct folio *folio; + int drained = 0; long i = 0; for (folio = pofs_get_folio(pofs, i); folio; @@ -2307,10 +2307,17 @@ static unsigned long collect_longterm_unpinnable_folios( continue; } - if (drain_allow && folio_ref_count(folio) != - folio_expected_ref_count(folio) + 1) { + if (drained == 0 && + folio_ref_count(folio) != + folio_expected_ref_count(folio) + 1) { + lru_add_drain(); + drained = 1; + } + if (drained == 1 && + folio_ref_count(folio) != + folio_expected_ref_count(folio) + 1) { lru_add_drain_all(); - drain_allow = false; + drained = 2; } if (!folio_isolate_lru(folio)) -- 2.51.0