Re: mlockall(MCL_FUTURE) implies MAP_POPULATE

["Jörn Engel" <joern-BHEL68pLQRGGvPXPguhicg@public.gmane.org>]

On Wed, Dec 16, 2015 at 07:44:16PM +0100, Michael Kerrisk (man7.org) wrote:
> On 28 October 2015 at 02:05, Jörn Engel <joern-BHEL68pLQRGGvPXPguhicg@public.gmane.org> wrote:
> > Hello Michael!
> >
> > Just came across this.  When reading the manpage MLOCK(2), I assume that
> > mlockall(MCL_FUTURE) does _not_ imply MAP_POPULATE.  But when reading
> > the code, I see that it does.
> >
> > This little detail can be rather crucial for RT-people, so it might be
> > worth spelling it out explicitly in the manpage.
> 
> But, this detail doesn't seem so surprising to me. MCL_FUTURE == new
> pages that are mapped will be locked. Of course they must be populated
> into memory when the mapping is created. Or: to put it another way,
> maybe it would help if you explain why you find the behavior
> surprising. That might give me a clue about what should be fixed in
> the man page.
> 
> But, please take this thread to mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, and cc
> linux-man-u79uwXL29TaiAVqoAR/hOA@public.gmane.org

Done. :)

I guess it is a judgement call now.  One fool (me) made the wrong
assumption and had to a) get into an argument with a coworker and b)
check the code to realize the mistake.  If fools like me are common, it
might be worth making this point explicit.  If I am the oddball, it
would be wasting file size and reading time for everyone else.

Jörn

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