linux-kernel - Re: [PATCH v3 2/2] Documentation/vm: Include kernel-doc to highmem.rst

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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
>