Re: [PATCH] recognize MAP_LOCKED in mmap() call

From: Andrew Morton (
Date: Wed Sep 18 2002 - 14:54:06 EST 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?

Linux does lock these regions. SuS seems to imply that we shouldn't.
But we should.

> 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?

That mlockall should have faulted everything in. It could be an
accounting bug, or it could be a bug. That's not an aspect which
gets tested a lot. I'll take a look.
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