[merged mm-stable] mm-reimplement-compound_order.patch removed from -mm tree

[merged mm-stable] mm-reimplement-compound_order.patch removed from -mm tree

[Andrew Morton]

The quilt patch titled
     Subject: mm: reimplement compound_order()
has been removed from the -mm tree.  Its filename was
     mm-reimplement-compound_order.patch

This patch was dropped because it was merged into the mm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Subject: mm: reimplement compound_order()
Date: Wed, 11 Jan 2023 14:29:02 +0000

Make compound_order() use struct folio.  It can't be turned into a wrapper
around folio_order() as a page can be turned into a tail page between a
check in compound_order() and the assertion in folio_test_large().

Link: https://lkml.kernel.org/r/20230111142915.1001531-17-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---


--- a/include/linux/mm.h~mm-reimplement-compound_order
+++ a/include/linux/mm.h
@@ -719,11 +719,20 @@ int vma_is_stack_for_current(struct vm_a
 struct mmu_gather;
 struct inode;
 
+/*
+ * compound_order() can be called without holding a reference, which means
+ * that niceties like page_folio() don't work.  These callers should be
+ * prepared to handle wild return values.  For example, PG_head may be
+ * set before _folio_order is initialised, or this may be a tail page.
+ * See compaction.c for some good examples.
+ */
 static inline unsigned int compound_order(struct page *page)
 {
-	if (!PageHead(page))
+	struct folio *folio = (struct folio *)page;
+
+	if (!test_bit(PG_head, &folio->flags))
 		return 0;
-	return page[1].compound_order;
+	return folio->_folio_order;
 }
 
 /**
_

Patches currently in -mm which might be from willy@infradead.org are