Re: [PATCH] mm: avoid livelock on !__GFP_FS allocations

[David Rientjes <rientjes@google.com>]

On Wed, 16 Nov 2011, Pekka Enberg wrote:

> > diff --git a/kernel/power/suspend.c b/kernel/power/suspend.c
> > index fdd4263..01aa9b5 100644
> > --- a/kernel/power/suspend.c
> > +++ b/kernel/power/suspend.c
> > @@ -297,9 +297,11 @@ int enter_state(suspend_state_t state)
> >                goto Finish;
> > 
> >        pr_debug("PM: Entering %s sleep\n", pm_states[state]);
> > +       oom_killer_disable();
> >        pm_restrict_gfp_mask();
> >        error = suspend_devices_and_enter(state);
> >        pm_restore_gfp_mask();
> > +       oom_killer_enable();
> > 
> >  Finish:
> >        pr_debug("PM: Finishing wakeup.\n");
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 6e8ecb6..d8c31b7 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -2177,9 +2177,9 @@ rebalance:
> >         * running out of options and have to consider going OOM
> >         */
> >        if (!did_some_progress) {
> > -               if ((gfp_mask & __GFP_FS) && !(gfp_mask & __GFP_NORETRY)) {
> > -                       if (oom_killer_disabled)
> > +               if (oom_killer_disabled)
> >                                goto nopage;

You're allowing __GFP_NOFAIL allocations to fail.

> > +               if ((gfp_mask & __GFP_FS) && !(gfp_mask & __GFP_NORETRY)) {
> >                        page = __alloc_pages_may_oom(gfp_mask, order,
> >                                        zonelist, high_zoneidx,
> >                                        nodemask, preferred_zone,
> > 
> 
> I'd prefer something like this. The whole 'gfp_allowed_flags' thing was
> designed to make GFP_KERNEL work during boot time where it's obviously safe to
> do that. I really don't think that's going to work suspend cleanly.
> 

Adding Rafael to the cc.

This has been done since 2.6.34 and presumably has been working quite 
well.  I don't have a specific objection to gfp_allowed_flags to be used 
outside of boot since it seems plausible that there are system-level 
contexts that would need different behavior in the page allocator and this 
does it effectively without major surgery or a slower fastpath.  Suspend 
is using it just like boot does before irqs are enabled, so I don't have 
an objection to it.

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