[PATCH RFC v3 03/19] mm: page_alloc: move prep_compound_page before post_alloc_hook

["Michael S. Tsirkin" <mst@redhat.com>]

Move prep_compound_page() before post_alloc_hook() in prep_new_page().

The next patch adds a folio_zero_user() call to post_alloc_hook(),
which uses folio_nr_pages() to determine how many pages to zero.
Without compound metadata set up first, folio_nr_pages() returns 1
for higher-order allocations, so only the first page would be zeroed.

All other operations in post_alloc_hook() (arch_alloc_page, KASAN,
debug, page owner, etc.) use raw page pointers with explicit order
counts and are unaffected by this reordering.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Assisted-by: Claude:claude-opus-4-6
Assisted-by: cursor-agent:GPT-5.4-xhigh
---
 mm/page_alloc.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 1cf5551849fe..99c01eb2d59e 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1895,11 +1895,11 @@ static void prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags
 							unsigned int alloc_flags,
 							unsigned long user_addr)
 {
-	post_alloc_hook(page, order, gfp_flags, user_addr);
-
 	if (order && (gfp_flags & __GFP_COMP))
 		prep_compound_page(page, order);
 
+	post_alloc_hook(page, order, gfp_flags, user_addr);
+
 	/*
 	 * page is set pfmemalloc when ALLOC_NO_WATERMARKS was necessary to
 	 * allocate the page. The expectation is that the caller is taking
-- 
MST