On 01.03.24 22:47, Matthew Wilcox (Oracle) wrote:
At least two places (memory failure and page migration) need to call
folio_test_hugetlb() without a reference on the folio. This can currently
result in false positives (returning true when the folio doesn't belong
to hugetlb) and more commonly in VM_BUG_ON() when a folio is split.
The new way to distinguish a hugetlb folio is to see if (1) the page
is compound (or the folio is large) and (2) page[1].mapping is set to
the address of hugetlb_lock. If the folio is (or has been) large then
page[1] is guaranteed to exist. If the folio is split between the two
tests, page[1].mapping will be set to something which definitely isn't
the address of hugetlb_lock.
Because we shift around the layout of struct folio a bit, we now use
page[1].private, which means we need to adjust __split_huge_page_tail()
a little. We also need to annoy the vmcore_info people again. Sorry.
Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
---
include/linux/mm_types.h | 4 +++-
include/linux/page-flags.h | 25 ++++---------------------
kernel/vmcore_info.c | 3 ++-
mm/huge_memory.c | 10 ++--------
mm/hugetlb.c | 24 ++++++++++++++++++++++++
5 files changed, 35 insertions(+), 31 deletions(-)
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index a7223ba3ea1e..fd80bf8b5d8a 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -289,6 +289,7 @@ typedef struct {
* @virtual: Virtual address in the kernel direct map.
* @_last_cpupid: IDs of last CPU and last process that accessed the folio.
* @_entire_mapcount: Do not use directly, call folio_entire_mapcount().
+ * @large_id: May identify the type of a large folio.
* @_nr_pages_mapped: Do not use directly, call folio_mapcount().
* @_pincount: Do not use directly, call folio_maybe_dma_pinned().
* @_folio_nr_pages: Do not use directly, call folio_nr_pages().
@@ -348,9 +349,9 @@ struct folio {
struct {
unsigned long _flags_1;
unsigned long _head_1;
- unsigned long _folio_avail;
/* public: */
atomic_t _entire_mapcount;
+ void *large_id;
atomic_t _nr_pages_mapped;
atomic_t _pincount;
Hm, I wanted that for the total mapcount. :(
Great that hugetlb makes things once again worse for everybody ... gah.
--
Cheers,
David / dhildenb
