linux-kernel - Re: [PATCH 2/2] mmap2: clarify MAP

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Message-ID: <5554A4D0.1020405@gmail.com>
Date:	Thu, 14 May 2015 15:36:16 +0200
From:	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To:	Michal Hocko <miso@...p22.suse.cz>
CC:	mtk.manpages@...il.com, Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux API <linux-api@...r.kernel.org>, linux-mm@...ck.org,
	Michal Hocko <mhocko@...e.cz>
Subject: Re: [PATCH 2/2] mmap2: clarify MAP_POPULATE

On 05/13/2015 04:38 PM, Michal Hocko wrote:
> From: Michal Hocko <mhocko@...e.cz>
> 
> David Rientjes has noticed that MAP_POPULATE wording might promise much
> more than the kernel actually provides and intend to provide. The
> primary usage of the flag is to pre-fault the range. There is no
> guarantee that no major faults will happen later on. The pages might
> have been reclaimed by the time the process tries to access them.

Yes, thanks, Michal -- that's a good point to make clearer.
Applied, with Reviewed-by: from Eric added.

Cheers,

Michael

> Signed-off-by: Michal Hocko <mhocko@...e.cz>
> ---
>  man2/mmap.2 | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/man2/mmap.2 b/man2/mmap.2
> index 1486be2e96b3..dcf306f2f730 100644
> --- a/man2/mmap.2
> +++ b/man2/mmap.2
> @@ -284,7 +284,7 @@ private writable mappings.
>  .BR MAP_POPULATE " (since Linux 2.5.46)"
>  Populate (prefault) page tables for a mapping.
>  For a file mapping, this causes read-ahead on the file.
> -Later accesses to the mapping will not be blocked by page faults.
> +This will help to reduce blocking on page faults later.
>  .BR MAP_POPULATE
>  is supported for private mappings only since Linux 2.6.23.
>  .TP
> 


-- 
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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