linux-kernel - [PATCH 3/4] Documentation/vm: Remove "Using kmap-atomic" from highmem.rst.

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Date:   Thu, 21 Apr 2022 20:01:59 +0200
From:   "Fabio M. De Francesco" <fmdefrancesco@...il.com>
To:     Ira Weiny <ira.weiny@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Catalin Marinas <catalin.marinas@....com>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Will Deacon <will@...nel.org>,
        Peter Collingbourne <pcc@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        linux-kernel@...r.kernel.org, Jonathan Corbet <corbet@....net>,
        linux-doc@...r.kernel.org, outreachy@...ts.linux.dev
Cc:     "Fabio M. De Francesco" <fmdefrancesco@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>
Subject: [PATCH 3/4] Documentation/vm: Remove "Using kmap-atomic" from highmem.rst.

The use of kmap_atomic() is deprecated in favor of kmap_local_page(). For
this reason the "Using kmap_atomic" section in highmem.rst is obsolete and
unnecessary.

Therefore, just remove it.

Cc: Jonathan Corbet <corbet@....net>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ira Weiny <ira.weiny@...el.com>
Cc: Matthew Wilcox <willy@...radead.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Fabio M. De Francesco <fmdefrancesco@...il.com>
---
 Documentation/vm/highmem.rst | 35 -----------------------------------
 1 file changed, 35 deletions(-)

diff --git a/Documentation/vm/highmem.rst b/Documentation/vm/highmem.rst
index ccff08a8211d..e05bf5524174 100644
--- a/Documentation/vm/highmem.rst
+++ b/Documentation/vm/highmem.rst
@@ -72,41 +72,6 @@ The kernel contains several ways of creating temporary mappings:
   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
 ==========================
 
-- 
2.34.1