Most callers of folio_test_clear_lru() then proceed to remove the folio from its lru, and add it back at the end when they're done (if still in use). But isolate_migratepages_block() and check_move_unevictable_pages() sometimes decide against, and release immediately with a folio_set_lru(). Which usually works fine: but there's now a small chance that while they held the folio with lru bit cleared, an lru_add fbatch drain came along, and had to skip that folio because its lru bit was transiently cleared (previously, the lru_add fbatch drain relied on finding lru bit never yet set). This risks leaving that folio off lru, unreclaimable until freed. Fix such cases by trying lru_add_del_folio() (which only takes action and returns true if the folio was on an lru_add fbatch), then folio_add_lru() if it succeeded: invalidating the old fbatch slot, appending in a new one. Signed-off-by: Hugh Dickins --- mm/compaction.c | 13 +++++++++++-- mm/vmscan.c | 16 +++++++++------- 2 files changed, 20 insertions(+), 9 deletions(-) diff --git a/mm/compaction.c b/mm/compaction.c index a049415512c6..9e045a90ba21 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -1204,7 +1204,13 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, !cc->alloc_contig)) { low_pfn += folio_nr_pages(folio) - 1; nr_scanned += folio_nr_pages(folio) - 1; - folio_set_lru(folio); + if (lru_add_del_folio(folio)) { + lruvec_unlock_irqrestore(locked, flags); + folio_add_lru(folio); + locked = NULL; + } else { + folio_set_lru(folio); + } goto isolate_fail_put; } } @@ -1293,7 +1299,10 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, if (locked) lruvec_unlock_irqrestore(locked, flags); if (folio) { - folio_set_lru(folio); + if (lru_add_del_folio(folio)) + folio_add_lru(folio); + else + folio_set_lru(folio); folio_put(folio); } diff --git a/mm/vmscan.c b/mm/vmscan.c index 4ca9775ceee8..7da12ffbd3bd 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -8021,17 +8021,19 @@ void check_move_unevictable_folios(struct folio_batch *fbatch) folio_clear_unevictable(folio); lruvec_add_folio(lruvec, folio); pgrescued += nr_pages; + } else if (lru_add_del_folio(folio)) { + lruvec_unlock_irq(lruvec); + folio_add_lru(folio); + lruvec = NULL; } - folio_set_lru(folio); + if (lruvec) + folio_set_lru(folio); } - if (lruvec) { - __count_vm_events(UNEVICTABLE_PGRESCUED, pgrescued); - __count_vm_events(UNEVICTABLE_PGSCANNED, pgscanned); + if (lruvec) lruvec_unlock_irq(lruvec); - } else if (pgscanned) { - count_vm_events(UNEVICTABLE_PGSCANNED, pgscanned); - } + count_vm_events(UNEVICTABLE_PGRESCUED, pgrescued); + count_vm_events(UNEVICTABLE_PGSCANNED, pgscanned); } EXPORT_SYMBOL_GPL(check_move_unevictable_folios); -- 2.51.0