From: Shivam Kalra <[email protected]> A shmem folio is removed from its page cache when it is written to swap. While it remains in the swap cache, it has no address_space mapping, so folio_check_splittable() mistakes it for a truncated folio and rejects the split with -EBUSY.
Allow a mappingless folio when it is in the swap cache. Initialize the XArray state without an address-space mapping, then assign the XArray only for mapped file folios. The split path already replaces each split folio in the swap cache while holding the swap-cluster lock. Signed-off-by: Shivam Kalra <[email protected]> --- mm/huge_memory.c | 18 +++++++----------- 1 file changed, 7 insertions(+), 11 deletions(-) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 804b8f6aa557..ecfe40b1400b 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -3882,12 +3882,10 @@ int folio_check_splittable(struct folio *folio, unsigned int new_order, VM_WARN_ON_FOLIO(!folio_test_locked(folio), folio); /* * Folios that just got truncated cannot get split. Signal to the - * caller that there was a race. - * - * TODO: this will also currently refuse folios without a mapping in the - * swapcache (shmem or to-be-anon folios). + * caller that there was a race. A mappingless swapcache folio can be + * either shmem or not yet associated with an anon_vma, and is valid. */ - if (!folio->mapping && !folio_test_anon(folio)) + if (!folio->mapping && !folio_test_swapcache(folio)) return -EBUSY; /* order-1 is not supported for anonymous THP. */ @@ -4022,10 +4020,7 @@ static int __folio_freeze_and_split_unmapped(struct folio *folio, unsigned int n if (do_lru) lru_add_split_folio(folio, new_folio, lruvec, list); - /* - * Anonymous folio with swap cache. - * NOTE: shmem in swap cache is not supported yet. - */ + /* Folio in the swap cache. */ if (ci) { __swap_cache_replace_folio(ci, folio, new_folio); continue; @@ -4103,7 +4098,7 @@ static int __folio_split(struct folio *folio, unsigned int new_order, struct page *split_at, struct page *lock_at, struct list_head *list, enum split_type split_type) { - XA_STATE(xas, &folio->mapping->i_pages, folio->index); + XA_STATE(xas, NULL, folio->index); struct folio *end_folio = folio_next(folio); bool is_anon = folio_test_anon(folio); struct mem_cgroup *memcg, *old_memcg; @@ -4158,11 +4153,12 @@ static int __folio_split(struct folio *folio, unsigned int new_order, } anon_vma_lock_write(anon_vma); mapping = NULL; - } else { + } else if (folio->mapping) { unsigned int min_order; gfp_t gfp; mapping = folio->mapping; + xas.xa = &mapping->i_pages; min_order = mapping_min_folio_order(mapping); if (new_order < min_order) { ret = -EINVAL; -- 2.43.0
