[PATCH] mremap.2: Add note about mremap with locked areas

[PATCH] mremap.2: Add note about mremap with locked areas

[Eric B Munson]

When mremap() is used to move or expand a mapping that is locked with
mlock() or equivalent it will attempt to populate the new area.
However, like mmap(MAP_LOCKED), mremap() will not fail if the area
cannot be populated.  Also like mmap(MAP_LOCKED) this might come as a
surprise to users and should be noted.

Signed-off-by: Eric B Munson <emunson@akamai.com>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: David Rientjes <rientjes@google.com>
Cc: linux-man@vger.kernel.org
Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org
---
 man2/mremap.2 | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/man2/mremap.2 b/man2/mremap.2
index 071adb5..cf884e6 100644
--- a/man2/mremap.2
+++ b/man2/mremap.2
@@ -196,6 +196,17 @@ and the prototype for
 did not allow for the
 .I new_address
 argument.
+
+If
+.BR mremap ()
+is used to move or expand an area locked with
+.BR mlock (2)
+or equivalent, the
+.BR mremap ()
+call will make a best effort to populate the new area but will not fail
+with
+.B ENOMEM
+if the area cannot be populated.
 .SH SEE ALSO
 .BR brk (2),
 .BR getpagesize (2),
-- 
1.9.1

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Re: [PATCH] mremap.2: Add note about mremap with locked areas

[Michal Hocko]

On Fri 28-08-15 14:42:52, Eric B Munson wrote:
> When mremap() is used to move or expand a mapping that is locked with
> mlock() or equivalent it will attempt to populate the new area.
> However, like mmap(MAP_LOCKED), mremap() will not fail if the area
> cannot be populated.  Also like mmap(MAP_LOCKED) this might come as a
> surprise to users and should be noted.
> 
> Signed-off-by: Eric B Munson <emunson-JqFfY2XvxFXQT0dZR+AlfA@public.gmane.org>
> Cc: Michal Hocko <mhocko-AlSwsSmVLrQ@public.gmane.org>

Acked-by: Michal Hocko <mhocko-IBi9RG/b67k@public.gmane.org>

Thank you for following on this.

> Cc: David Rientjes <rientjes-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
> Cc: linux-man-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
> Cc: linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org
> Cc: linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
> ---
>  man2/mremap.2 | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/man2/mremap.2 b/man2/mremap.2
> index 071adb5..cf884e6 100644
> --- a/man2/mremap.2
> +++ b/man2/mremap.2
> @@ -196,6 +196,17 @@ and the prototype for
>  did not allow for the
>  .I new_address
>  argument.
> +
> +If
> +.BR mremap ()
> +is used to move or expand an area locked with
> +.BR mlock (2)
> +or equivalent, the
> +.BR mremap ()
> +call will make a best effort to populate the new area but will not fail
> +with
> +.B ENOMEM
> +if the area cannot be populated.
>  .SH SEE ALSO
>  .BR brk (2),
>  .BR getpagesize (2),
> -- 
> 1.9.1

-- 
Michal Hocko
SUSE Labs
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Re: [PATCH] mremap.2: Add note about mremap with locked areas

[Michael Kerrisk (man-pages)]

On 08/28/2015 08:42 PM, Eric B Munson wrote:
> When mremap() is used to move or expand a mapping that is locked with
> mlock() or equivalent it will attempt to populate the new area.
> However, like mmap(MAP_LOCKED), mremap() will not fail if the area
> cannot be populated.  Also like mmap(MAP_LOCKED) this might come as a
> surprise to users and should be noted.

Thanks, Eric! 

Applied, with Michael's Acked-by added.

Cheers,

Michael


> Signed-off-by: Eric B Munson <emunson-JqFfY2XvxFXQT0dZR+AlfA@public.gmane.org>
> Cc: Michal Hocko <mhocko-AlSwsSmVLrQ@public.gmane.org>
> Cc: David Rientjes <rientjes-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
> Cc: linux-man-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
> Cc: linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org
> Cc: linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
> ---
>  man2/mremap.2 | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/man2/mremap.2 b/man2/mremap.2
> index 071adb5..cf884e6 100644
> --- a/man2/mremap.2
> +++ b/man2/mremap.2
> @@ -196,6 +196,17 @@ and the prototype for
>  did not allow for the
>  .I new_address
>  argument.
> +
> +If
> +.BR mremap ()
> +is used to move or expand an area locked with
> +.BR mlock (2)
> +or equivalent, the
> +.BR mremap ()
> +call will make a best effort to populate the new area but will not fail
> +with
> +.B ENOMEM
> +if the area cannot be populated.
>  .SH SEE ALSO
>  .BR brk (2),
>  .BR getpagesize (2),
> 


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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