Re: slab: setup allocators earlier in the boot sequence

Pekka Enberg
2009-06-12T07:59:58Z

Hi Nick,

On Fri, Jun 12, 2009 at 10:45:45AM +0300, Pekka Enberg wrote:
> > On Fri, 2009-06-12 at 17:34 +1000, Benjamin Herrenschmidt wrote:
> > > I really believe this should be a slab internal thing, which is what my
> > > patch does to a certain extent. IE. All callers need to care about is
> > > KERNEL vs. ATOMIC and in some cases, NOIO or similar for filesystems
> > > etc... but I don't think all sorts of kernel subsystems, because they
> > > can be called early during boot, need to suddenly use GFP_NOWAIT all the
> > > time.
> > >
> > > That's why I much prefer my approach :-) (In addition to the fact that
> > > it provides the basis for also fixing suspend/resume).
> >
> > Sure, I think we can do what you want with the patch below.

On Fri, 2009-06-12 at 09:54 +0200, Nick Piggin wrote:
> I don't really like adding branches to slab allocator like this.
> init code all needs to know what services are available, and
> this includes the scheduler if it wants to do anything sleeping
> (including sleeping slab allocations).
>
> Core mm code is the last place to put in workarounds for broken
> callers...

Yes, the initialization code can be fixed to use GFP_NOWAIT. But it's
really the suspend case that makes me think the patch might be a good
idea. So the patch does not attempt to be a workaround for buggy callers
but rather a change in policy that we simply refuse to wait during
bootup and suspend.

Pekka