Re: [PATCH 2/2] mmap2: clarify MAP_POPULATE
From: Michael Kerrisk (man-pages)
Date: Thu May 14 2015 - 09:36:31 EST
On 05/13/2015 04:38 PM, Michal Hocko wrote:
> From: Michal Hocko <mhocko@xxxxxxx>
> 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.
> Signed-off-by: Michal Hocko <mhocko@xxxxxxx>
> 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.
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