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@xxxxxxxxx>
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@xxxxxxxxxxxxxxxxxxxxxxxxx/
Link: https://lkml.kernel.org/r/20220124013045.806718-1-ira.weiny@xxxxxxxxx
Signed-off-by: Ira Weiny <ira.weiny@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
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@xxxxxxxxx are
highmem-document-kunmap_local.patch
