Re: [linux-pm] Re: Hibernation considerations

[david@lang.hm]

On Fri, 20 Jul 2007, Jim Crilly wrote:

> > > has
> > > requested the image to be not greater than 50% of RAM.  In that case you
> > > have
> > > to free some memory _before_ identifying memory to save and you must not
> > > race with applications that attempt to allocate memory while you're doing
> > > it.
> >
> > I disagree a little bit.
> >
> > first off, only the suspending kernel can know what can be freed and what
> > is needed to do so (remember this is kernel internals, it can change from
> > patch to patch, let alone version to version)
> >
> > second, if you have a lot of memory to free, and you can't just throw away
> > caches to do so, you don't know what is going to be involved in freeing
> > the memory, it's very possilbe that it is going to involve userspace, so
> > you can't freeze any significant portion of the system, so you can't
> > eliminate all chance of races
> >
> > what you can do is
> >
> > 1. try to free stuff
> > 2. stop the system and account for memory, is enough free
> > if not goto 1
> >
> > if userspace is dirtying memory fast enough, or is just useing enough
> > memory that you can't meet your limit you just won't be able to suspend.
> >
> > but under any other conditions you will eventually get enough memory free.
> >
> > so try several times and if you still fail tell the user they have too
> > much stuff running and they need to kill something.
>
> Which would be a pretty big regression from what we have now. With the
> current implementation I can hibernate under virtually any workload because
> the freezer stops everything and there's no competition for resources.

as long as what you are trying to save is <=50% of ram (at least with some 
implementations). if you are trying to save more then 50% of ram with some 
current implmenetations you just can't

David Lang
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/