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SubjectRe: [PATCH] recognize MAP_LOCKED in mmap() call
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On Wednesday 18 September 2002 03:18 pm, Mark_H_Johnson@raytheon.com wrote:
> Andrew Morton wrote:
> >(SuS really only anticipates that mmap needs to look at prior mlocks
> >in force against the address range. It also says
> >
> > Process memory locking does apply to shared memory regions,
> >
> >and we don't do that either. I think we should; can't see why SuS
> >requires this.)
>
> Let me make sure I read what you said correctly. Does this mean that Linux
> 2.4 (or 2.5) kernels do not lock shared memory regions if a process uses
> mlockall?
>
> If not, that is *really bad* for our real time applications. We don't want
> to take a page fault while running some 80hz task, just because some
> non-real time application tried to use what little physical memory we allow
> for the kernel and all other applications.
>
> I asked a related question about a week ago on linux-mm and didn't get a
> response. Basically, I was concerned that top did not show RSS == Size when
> mlockall(MCL_CURRENT|MCL_FUTURE) was called. Could this explain the
> difference or is there something else that I'm missing here?
>
> Thanks.
> --Mark H Johnson
> <mailto:Mark_H_Johnson@raytheon.com>


Sorry for the lengthy delay.
mlock() and mlockall() do the right thing..
however, mmap(MAP_LOCKED) should behave like a mmap | mlock operation
according to the manpages. This however was not implemented as the
transformation from the mmap_flags to vm_flags never checked for MAP_LOCKED
but only for mm->def_flags which only covers a previous mlockall() call.

Hope this clarifies it .
--
-- Hubertus Franke (frankeh@watson.ibm.com)
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