On 7/13/21 1:02 AM, Mike Kravetz wrote:

On 6/17/21 11:44 AM, Joao Martins wrote:

quoted

Split the utility function prep_compound_page() into head and tail
counterparts, and use them accordingly.

This is in preparation for sharing the storage for / deduplicating
compound page metadata.

Signed-off-by: Joao Martins <redacted>
---
 mm/page_alloc.c | 32 +++++++++++++++++++++-----------
 1 file changed, 21 insertions(+), 11 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 8836e54721ae..95967ce55829 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c

@@ -741,24 +741,34 @@ void free_compound_page(struct page *page)
 	free_the_page(page, compound_order(page));
 }
 
+static void prep_compound_head(struct page *page, unsigned int order)
+{
+	set_compound_page_dtor(page, COMPOUND_PAGE_DTOR);
+	set_compound_order(page, order);
+	atomic_set(compound_mapcount_ptr(page), -1);
+	if (hpage_pincount_available(page))
+		atomic_set(compound_pincount_ptr(page), 0);
+}
+
+static void prep_compound_tail(struct page *head, int tail_idx)
+{
+	struct page *p = head + tail_idx;
+
+	set_page_count(p, 0);

When you rebase, you should notice this has been removed from
prep_compound_page as all tail pages should have zero ref count.

/me nods

quoted

+	p->mapping = TAIL_MAPPING;
+	set_compound_head(p, head);
+}
+
 void prep_compound_page(struct page *page, unsigned int order)
 {
 	int i;
 	int nr_pages = 1 << order;
 
 	__SetPageHead(page);
-	for (i = 1; i < nr_pages; i++) {
-		struct page *p = page + i;
-		set_page_count(p, 0);
-		p->mapping = TAIL_MAPPING;
-		set_compound_head(p, page);
-	}
+	for (i = 1; i < nr_pages; i++)
+		prep_compound_tail(page, i);
 
-	set_compound_page_dtor(page, COMPOUND_PAGE_DTOR);
-	set_compound_order(page, order);
-	atomic_set(compound_mapcount_ptr(page), -1);
-	if (hpage_pincount_available(page))
-		atomic_set(compound_pincount_ptr(page), 0);
+	prep_compound_head(page, order);
 }
 
 #ifdef CONFIG_DEBUG_PAGEALLOC

I'll need something like this for demote hugetlb page fuinctionality
when the pages being demoted have been optimized for minimal vmemmap
usage.

Acked-by: Mike Kravetz <redacted>

Thanks!