Re: [RFC 1/3] mm: mmap make MAP_LOCKED really mlock semantic

From: Andrew Morton
Date: Tue Apr 28 2015 - 19:10:09 EST

On Tue, 28 Apr 2015 14:11:49 +0200 Michal Hocko <mhocko@xxxxxxx> wrote:

> The man page however says
> "
> MAP_LOCKED (since Linux 2.5.37)
> Lock the pages of the mapped region into memory in the manner of
> mlock(2). This flag is ignored in older kernels.
> "

I'm trying to remember why we implemented MAP_LOCKED in the first
place. Was it better than mmap+mlock in some fashion?

afaict we had a #define MAP_LOCKED in the header file but it wasn't
implemented, so we went and wired it up. 13 years ago:

Anyway... the third way of doing this is to use plain old mmap() while
mlockall(MCL_FUTURE) is in force. Has anyone looked at that, checked
that the behaviour is sane and compared it with the mmap+mlock
behaviour, the MAP_LOCKED behaviour and the manpages?

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