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The list check sits behind the > flag test because order-1 folios have no _deferred_list. > > folio_order() is safe to use at this point in the split process: it > still shows the pre-split order. > > Suggested-by: David Hildenbrand (Arm) > Assisted-by: Claude-Code:claude-fable-5-1 > Signed-off-by: Kiryl Shutsemau (Meta) > --- > mm/huge_memory.c | 31 ++++++++++++++++++++----------- > 1 file changed, 20 insertions(+), 11 deletions(-) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index dd66c6ad5af1..23ef22c2b5db 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -3972,6 +3972,24 @@ static unsigned int folio_cache_ref_count(const struct folio *folio) > return folio_nr_pages(folio); > } > > +static void folio_reset_partially_mapped(struct folio *folio) > +{ > + VM_WARN_ON_FOLIO(folio_ref_count(folio), folio); > + > + if (!folio_test_partially_mapped(folio)) > + return; > + > + /* > + * Order-1 folios have no _deferred_list. The flag is only ever set > + * on folios that do, so the list can be checked after the flag. > + */ > + VM_WARN_ON_FOLIO(!list_empty(&folio->_deferred_list), folio); > + > + folio_clear_partially_mapped(folio); > + mod_mthp_stat(folio_order(folio), > + MTHP_STAT_NR_ANON_PARTIALLY_MAPPED, -1); > +} > + > static int __folio_freeze_and_split_unmapped(struct folio *folio, unsigned int new_order, > struct page *split_at, struct xa_state *xas, > struct address_space *mapping, bool do_lru, > @@ -3980,7 +3998,6 @@ static int __folio_freeze_and_split_unmapped(struct folio *folio, unsigned int n > { > struct folio *end_folio = folio_next(folio); > struct folio *new_folio, *next; > - int old_order = folio_order(folio); > int ret = 0; > > VM_WARN_ON_ONCE(!mapping && end); > @@ -3998,11 +4015,7 @@ static int __folio_freeze_and_split_unmapped(struct folio *folio, unsigned int n > * leaves PG_partially_mapped set. > * Clear it here: the flag does not survive the split. > */ > - if (folio_test_partially_mapped(folio)) { > - folio_clear_partially_mapped(folio); > - mod_mthp_stat(old_order, > - MTHP_STAT_NR_ANON_PARTIALLY_MAPPED, -1); > - } > + folio_reset_partially_mapped(folio); > > if (mapping) { > int nr = folio_nr_pages(folio); > @@ -4516,11 +4529,7 @@ bool __folio_unqueue_deferred_split(struct folio *folio) > memcg = folio_memcg(folio); > lru = list_lru_lock_irqsave(&deferred_split_lru, nid, &memcg, &flags); > if (__list_lru_del(&deferred_split_lru, lru, &folio->_deferred_list, nid)) { > - if (folio_test_partially_mapped(folio)) { > - folio_clear_partially_mapped(folio); > - mod_mthp_stat(folio_order(folio), > - MTHP_STAT_NR_ANON_PARTIALLY_MAPPED, -1); > - } > + folio_reset_partially_mapped(folio); > unqueued = true; > } > list_lru_unlock_irqrestore(lru, &flags); > > base-commit: e3fc12b08aadde9cec7b3799ac0e0c9a1aa245c4 Makes sense Acked-by: Balbir Singh