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>> 2. if the given list is NULL, the folio is on LRU. >> >> And the rule is buried deeply in lru_add_split_folio(). >> >> Should we add some checks in __folio_split()? >> >> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >> index d3e66136e41a..8ce2734c9ca0 100644 >> --- a/mm/huge_memory.c >> +++ b/mm/huge_memory.c >> @@ -3732,6 +3732,11 @@ static int __folio_split(struct folio *folio, u= nsigned int new_order, >> VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio); >> VM_BUG_ON_FOLIO(!folio_test_large(folio), folio); >> >> + if (list && folio_test_lru(folio)) >> + return -EINVAL; >> + if (!list && !folio_test_lru(folio)) >> + return -EINVAL; >> + > > I guess we currently don't run into that, because whenever a folio is o= therwise isolated, there is an additional reference or a page table mappi= ng, so it cannot get split either way (e.g., freezing the refcount fails)= =2E > > So maybe these checks would be too early and they should happen after w= e froze the refcount? But if the caller does the isolation, the additional refcount is OK and can_split_folio() will return true. In addition, __folio_split() does not= change folio LRU state, so these two checks are orthogonal to refcount check, right? The placement of them does not matter, but earlier the bett= er to avoid unnecessary work. I see these are sanity checks for callers. Best Regards, Yan, Zi