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.
+ */
__SetPageHead(head);
for (pfn = head_pfn + 1; pfn < end_pfn; pfn++) {
struct page *page = pfn_to_page(pfn);
@@ -1098,15 +1102,8 @@ static void __ref memmap_init_compound(struct page *head,
__init_zone_device_page(page, pfn, zone_idx, nid, pgmap);
prep_compound_tail(head, pfn - head_pfn);
set_page_count(page, 0);
-
- /*
- * The first tail page stores important compound page info.
- * Call prep_compound_head() after the first tail page has
- * been initialized, to not have the data overwritten.
- */
- if (pfn == head_pfn + 1)
- prep_compound_head(head, order);
}
+ prep_compound_head(head, order);
}
void __ref memmap_init_zone_device(struct zone *zone,
--
2.50.1
