On 22.08.25 17:27, Mike Rapoport wrote:
On Thu, Aug 21, 2025 at 10:06:35PM +0200, David Hildenbrand wrote:
Grepping for "prep_compound_page" leaves on clueless how devdax gets its
compound pages initialized.
Let's add a comment that might help finding this open-coded
prep_compound_page() initialization more easily.
Further, let's be less smart about the ordering of initialization and just
perform the prep_compound_head() call after all tail pages were
initialized: just like prep_compound_page() does.
No need for a lengthy comment then: again, just like prep_compound_page().
Note that prep_compound_head() already does initialize stuff in page[2]
through prep_compound_head() that successive tail page initialization
will overwrite: _deferred_list, and on 32bit _entire_mapcount and
_pincount. Very likely 32bit does not apply, and likely nobody ever ends
up testing whether the _deferred_list is empty.
So it shouldn't be a fix at this point, but certainly something to clean
up.
Signed-off-by: David Hildenbrand <da...@redhat.com>
---
mm/mm_init.c | 13 +++++--------
1 file changed, 5 insertions(+), 8 deletions(-)
diff --git a/mm/mm_init.c b/mm/mm_init.c
index 5c21b3af216b2..708466c5b2cc9 100644
--- a/mm/mm_init.c
+++ b/mm/mm_init.c
@@ -1091,6 +1091,10 @@ static void __ref memmap_init_compound(struct page *head,
unsigned long pfn, end_pfn = head_pfn + nr_pages;
unsigned int order = pgmap->vmemmap_shift;
+ /*
+ * This is an open-coded prep_compound_page() whereby we avoid
+ * walking pages twice by initializing them in the same go.
+ */
While on it, can you also mention that prep_compound_page() is not used to
properly set page zone link?
Sure, thanks!
--
Cheers
David / dhildenb
