+ mm-page_alloc-add-__free_pages-documentation.patch added to -mm tree

+ mm-page_alloc-add-__free_pages-documentation.patch added to -mm tree

[akpm]

The patch titled
     Subject: mm/page_alloc: add __free_pages() documentation
has been added to the -mm tree.  Its filename is
     mm-page_alloc-add-__free_pages-documentation.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/mm-page_alloc-add-__free_pages-documentation.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/mm-page_alloc-add-__free_pages-documentation.patch

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------------------------------------------------------
From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Subject: mm/page_alloc: add __free_pages() documentation

Provide some guidance towards when this might not be the right interface
to use.

Link: https://lkml.kernel.org/r/20201027025523.3235-1-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/page_alloc.c |   20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

--- a/mm/page_alloc.c~mm-page_alloc-add-__free_pages-documentation
+++ a/mm/page_alloc.c
@@ -5034,6 +5034,26 @@ static inline void free_the_page(struct
 		__free_pages_ok(page, order, FPI_NONE);
 }
 
+/**
+ * __free_pages - Free pages allocated with alloc_pages().
+ * @page: The page pointer returned from alloc_pages().
+ * @order: The order of the allocation.
+ *
+ * This function can free multi-page allocations that are not compound
+ * pages.  It does not check that the @order passed in matches that of
+ * the allocation, so it is easy to leak memory.  Freeing more memory
+ * than was allocated will probably emit a warning.
+ *
+ * If the last reference to this page is speculative, it will be released
+ * by put_page() which only frees the first page of a non-compound
+ * allocation.  To prevent the remaining pages from being leaked, we free
+ * the subsequent pages here.  If you want to use the page's reference
+ * count to decide when to free the allocation, you should allocate a
+ * compound page, and use put_page() instead of __free_pages().
+ *
+ * Context: May be called in interrupt context or while holding a normal
+ * spinlock, but not in NMI context or while holding a raw spinlock.
+ */
 void __free_pages(struct page *page, unsigned int order)
 {
 	if (put_page_testzero(page))
_

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

mm-fix-readahead_page_batch-for-retry-entries.patch
mm-fix-madvise-willneed-performance-problem.patch
mm-page-flags-fix-comment.patch
mm-page_alloc-add-__free_pages-documentation.patch