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Message-ID: <Yl3Y0F/WT5xKoJCt@iweiny-desk3>
Date: Mon, 18 Apr 2022 14:32:00 -0700
From: Ira Weiny <ira.weiny@...el.com>
To: "Fabio M. De Francesco" <fmdefrancesco@...il.com>
Cc: Jonathan Corbet <corbet@....net>,
Andrew Morton <akpm@...ux-foundation.org>,
SeongJae Park <sj@...nel.org>,
Jiajian Ye <yejiajian2018@...il.szu.edu.cn>,
Thomas Gleixner <tglx@...utronix.de>,
Matthew Wilcox <willy@...radead.org>,
Peter Zijlstra <peterz@...radead.org>,
outreachy@...ts.linux.dev, linux-doc@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/2] Documentation/vm: Include kernel-doc to
highmem.rst
On Sat, Apr 16, 2022 at 01:19:17AM +0200, Fabio M. De Francesco wrote:
> Include kernel-doc comments to highmem.rst from
> include/kernel/highmem.h.
>
> From now on, the "Using kmap_atomic" section is redundant and obsolete,
> therefore 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>
Reviewed-by: Ira Weiny <ira.weiny@...el.com>
> ---
> Documentation/vm/highmem.rst | 41 ++++++------------------------------
> 1 file changed, 6 insertions(+), 35 deletions(-)
>
> diff --git a/Documentation/vm/highmem.rst b/Documentation/vm/highmem.rst
> index 12dcfbee094d..5dcee6233cd5 100644
> --- a/Documentation/vm/highmem.rst
> +++ b/Documentation/vm/highmem.rst
> @@ -117,41 +117,6 @@ The kernel contains several ways of creating temporary mappings:
> synchronization to unmap.
>
>
> -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
> ==========================
>
> @@ -190,3 +155,9 @@ The general recommendation is that you don't use more than 8GiB on a 32-bit
> machine - although more might work for you and your workload, you're pretty
> much on your own - don't expect kernel developers to really care much if things
> come apart.
> +
> +
> +Functions
> +=========
> +
> +.. kernel-doc:: include/linux/highmem.h
> --
> 2.34.1
>
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