Because THP_SWAP uses page->private for each page, we must not use
the space which overlaps that field for anything which would conflict
with that. We avoid the conflict on 32-bit systems by disallowing
THP_SWAP on 32-bit.
Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
---
include/linux/mm_types.h | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 659c7b84726c..3880b3f2e321 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -340,8 +340,11 @@ struct folio {
atomic_t _pincount;
#ifdef CONFIG_64BIT
unsigned int _folio_nr_pages;
-#endif
+ /* 4 byte gap here */
/* private: the union with struct page is transitional */
+ /* Fix THP_SWAP to not use tail->private */
+ unsigned long _private_1;
+#endif
};
struct page __page_1;
};
@@ -362,6 +365,9 @@ struct folio {
/* public: */
struct list_head _deferred_list;
/* private: the union with struct page is transitional */
+ unsigned long _avail_2a;
+ /* Fix THP_SWAP to not use tail->private */
+ unsigned long _private_2a;
};
struct page __page_2;
};
@@ -386,12 +392,18 @@ FOLIO_MATCH(memcg_data, memcg_data);
offsetof(struct page, pg) + sizeof(struct page))
FOLIO_MATCH(flags, _flags_1);
FOLIO_MATCH(compound_head, _head_1);
+#ifdef CONFIG_64BIT
+FOLIO_MATCH(private, _private_1);
+#endif
#undef FOLIO_MATCH
#define FOLIO_MATCH(pg, fl) \
static_assert(offsetof(struct folio, fl) == \
offsetof(struct page, pg) + 2 * sizeof(struct page))
FOLIO_MATCH(flags, _flags_2);
FOLIO_MATCH(compound_head, _head_2);
+FOLIO_MATCH(flags, _flags_2a);
+FOLIO_MATCH(compound_head, _head_2a);
+FOLIO_MATCH(private, _private_2a);
#undef FOLIO_MATCH
/*
--
2.40.1
