+ highmem-document-kunmap_local.patch added to -mm tree

+ highmem-document-kunmap_local.patch added to -mm tree

[akpm]

The patch titled
     Subject: highmem: document kunmap_local()
has been added to the -mm tree.  Its filename is
     highmem-document-kunmap_local.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/highmem-document-kunmap_local.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/highmem-document-kunmap_local.patch

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------------------------------------------------------
From: Ira Weiny <ira.weiny@intel.com>
Subject: highmem: document kunmap_local()

Some users of kmap() add an offset to the kmap() address to be used during
the mapping.

When converting to kmap_local_page() the base address does not need to be
stored because any address within the page can be used in kunmap_local(). 
However, this was not clear from the documentation and caused some
questions.[1]

Document that any address in the page can be used in kunmap_local() to
clarify this for future users.

[1] https://lore.kernel.org/lkml/20211213154543.GM3538886@iweiny-DESK2.sc.intel.com/

Link: https://lkml.kernel.org/r/20220124013045.806718-1-ira.weiny@intel.com
Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/highmem-internal.h |   11 +++++++++++
 1 file changed, 11 insertions(+)

--- a/include/linux/highmem-internal.h~highmem-document-kunmap_local
+++ a/include/linux/highmem-internal.h
@@ -246,6 +246,17 @@ do {								\
 	__kunmap_atomic(__addr);				\
 } while (0)
 
+/**
+ * kunmap_local - Unmap a page mapped via kmap_local_page().
+ * @__addr: An address within the page mapped
+ *
+ * __addr is often an address returned from kmap_local_page().  However,
+ * this address can be any address within the mapped page.  It does not need to
+ * be the exact address returned from kmap_local_page()
+ *
+ * Unmapping should be done in the reverse order of the mapping.  See
+ * kmap_local_page() for details.
+ */
 #define kunmap_local(__addr)					\
 do {								\
 	BUILD_BUG_ON(__same_type((__addr), struct page *));	\
_

Patches currently in -mm which might be from ira.weiny@intel.com are

highmem-document-kunmap_local.patch