On Thu, Aug 28, 2025 at 12:01:13AM +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 comment to describe the initialization order: again, just like prep_compound_page().
Wow this is great, thank you for putting a quality comment for this and thinking of this :)
We have too much 'special case you just have to know' stuff sitting around, so this kind of thing is always great to see.
Reviewed-by: Mike Rapoport (Microsoft) rppt@kernel.org Signed-off-by: David Hildenbrand david@redhat.com
LGTM, so:
Reviewed-by: Lorenzo Stoakes lorenzo.stoakes@oracle.com
mm/mm_init.c | 15 +++++++-------- 1 file changed, 7 insertions(+), 8 deletions(-)
diff --git a/mm/mm_init.c b/mm/mm_init.c index 5c21b3af216b2..df614556741a4 100644 --- a/mm/mm_init.c +++ b/mm/mm_init.c @@ -1091,6 +1091,12 @@ static void __ref memmap_init_compound(struct page *head, unsigned long pfn, end_pfn = head_pfn + nr_pages; unsigned int order = pgmap->vmemmap_shift;
- /*
* We have to initialize the pages, including setting up page links.* prep_compound_page() does not take care of that, so instead we* open-code prep_compound_page() so we can take care of initializing* the pages in the same go.*/@@ -1098,15 +1104,8 @@ 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