linux-kernel - Re: [PATCH] mm: avoid livelock on !__GFP

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Date:	Thu, 17 Nov 2011 07:07:13 +0900
From:	Minchan Kim <barrioskmc@...il.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Pekka Enberg <penberg@...nel.org>,
	Minchan Kim <minchan.kim@...il.com>,
	Colin Cross <ccross@...roid.com>, Mel Gorman <mgorman@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Pekka Enberg <penberg@...helsinki.fi>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux-MM <linux-mm@...ck.org>, "Rafael J. Wysocki" <rjw@...k.pl>
Subject: Re: [PATCH] mm: avoid livelock on !__GFP_FS allocations

On Thu, Nov 17, 2011 at 6:44 AM, David Rientjes <rientjes@...gle.com> wrote:
> 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.
>

My point isn't using gfp_allowed_flags(maybe it's Pekka's concern) but
why adding new special case handling code like pm_suspended_storage.
I think we can handle the issue with oom_killer_disabled(but the naming is bad)

-- 
Kind regards,
Minchan Kim
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