Re: [PATCH V2] mm/gup: Clear the LRU flag of a page before adding to LRU batch

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Looking at this in more detail, I wonder if we can turn that to

if (!folio_test_clear_lru(folio))     return; folio_get(folio);

In all cases? The caller must hold a reference, so this should be fine.

Seems the caller madvise_free_pte_range(...), calling folio_mark_lazyfree(...), doesn't hold a reference on folio.

If that would be the case and the folio could get freed concurrently, the folio_get(folio) would be completely broken.

In madvise_free_pte_range() we hold the PTL, so the folio cannot get freed concurrently.

folio_get() is only allowed when we are sure the folio cannot get freed concurrently, because we know there is a reference that cannot go away.