The patch titled
Subject: Documentation/vm: move "Using kmap-atomic" to highmem.h
has been added to the -mm mm-unstable branch. Its filename is
documentation-vm-move-using-kmap-atomic-to-highmemh.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/documentation-vm-move-using-kmap-atomic-to-highmemh.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: "Fabio M. De Francesco" <fmdefrancesco@xxxxxxxxx>
Subject: Documentation/vm: move "Using kmap-atomic" to highmem.h
The use of kmap_atomic() is new code is being deprecated in favor of
kmap_local_page(). For this reason the "Using kmap_atomic" section in
highmem.rst is obsolete and unnecessary, but it can still help developers
if it were moved to kdocs in highmem.h.
Therefore, move the relevant parts of this section from highmem.rst and
merge them with the kdocs in highmem.h.
Link: https://lkml.kernel.org/r/20220428212455.892-4-fmdefrancesco@xxxxxxxxx
Signed-off-by: Fabio M. De Francesco <fmdefrancesco@xxxxxxxxx>
Suggested-by: Ira Weiny <ira.weiny@xxxxxxxxx>
Reviewed-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Reviewed-by: Ira Weiny <ira.weiny@xxxxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Mike Rapoport <rppt@xxxxxxxxxxxxx>
Cc: Peter Collingbourne <pcc@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/vm/highmem.rst | 35 ---------------------------------
include/linux/highmem.h | 31 +++++++++++++++++++++++++++++
2 files changed, 31 insertions(+), 35 deletions(-)
--- a/Documentation/vm/highmem.rst~documentation-vm-move-using-kmap-atomic-to-highmemh
+++ a/Documentation/vm/highmem.rst
@@ -72,41 +72,6 @@ The kernel contains several ways of crea
It may be assumed that k[un]map_atomic() won't fail.
-Using kmap_atomic
-=================
-
-When and where to use kmap_atomic() is straightforward. It is used when code
-wants to access the contents of a page that might be allocated from high memory
-(see __GFP_HIGHMEM), for example a page in the pagecache. The API has two
-functions, and they can be used in a manner similar to the following::
-
- /* Find the page of interest. */
- struct page *page = find_get_page(mapping, offset);
-
- /* Gain access to the contents of that page. */
- void *vaddr = kmap_atomic(page);
-
- /* Do something to the contents of that page. */
- memset(vaddr, 0, PAGE_SIZE);
-
- /* Unmap that page. */
- kunmap_atomic(vaddr);
-
-Note that the kunmap_atomic() call takes the result of the kmap_atomic() call
-not the argument.
-
-If you need to map two pages because you want to copy from one page to
-another you need to keep the kmap_atomic calls strictly nested, like::
-
- vaddr1 = kmap_atomic(page1);
- vaddr2 = kmap_atomic(page2);
-
- memcpy(vaddr1, vaddr2, PAGE_SIZE);
-
- kunmap_atomic(vaddr2);
- kunmap_atomic(vaddr1);
-
-
Cost of Temporary Mappings
==========================
--- a/include/linux/highmem.h~documentation-vm-move-using-kmap-atomic-to-highmemh
+++ a/include/linux/highmem.h
@@ -145,6 +145,37 @@ static inline void *kmap_local_folio(str
* Mappings should always be released by kunmap_atomic().
*
* Do not use in new code. Use kmap_local_page() instead.
+ *
+ * It is used in atomic context when code wants to access the contents of a
+ * page that might be allocated from high memory (see __GFP_HIGHMEM), for
+ * example a page in the pagecache. The API has two functions, and they
+ * can be used in a manner similar to the following:
+ *
+ * -- Find the page of interest. --
+ * struct page *page = find_get_page(mapping, offset);
+ *
+ * -- Gain access to the contents of that page. --
+ * void *vaddr = kmap_atomic(page);
+ *
+ * -- Do something to the contents of that page. --
+ * memset(vaddr, 0, PAGE_SIZE);
+ *
+ * -- Unmap that page. --
+ * kunmap_atomic(vaddr);
+ *
+ * Note that the kunmap_atomic() call takes the result of the kmap_atomic()
+ * call, not the argument.
+ *
+ * If you need to map two pages because you want to copy from one page to
+ * another you need to keep the kmap_atomic calls strictly nested, like:
+ *
+ * vaddr1 = kmap_atomic(page1);
+ * vaddr2 = kmap_atomic(page2);
+ *
+ * memcpy(vaddr1, vaddr2, PAGE_SIZE);
+ *
+ * kunmap_atomic(vaddr2);
+ * kunmap_atomic(vaddr1);
*/
static inline void *kmap_atomic(struct page *page);
_
Patches currently in -mm which might be from fmdefrancesco@xxxxxxxxx are
mm-highmem-fix-kernel-doc-warnings-in-highmemh.patch
documentation-vm-include-kdocs-from-highmemh-into-highmemrst.patch
documentation-vm-move-using-kmap-atomic-to-highmemh.patch
documentation-vm-rework-temporary-virtual-mappings-section.patch
