Re: [PATCH] mm,oom: do not loop !__GFP_FS allocation if the OOM killer is disabled.

[Johannes Weiner <hannes@cmpxchg.org>]

On Mon, Jan 11, 2016 at 06:20:58PM +0100, Michal Hocko wrote:
> On Mon 11-01-16 12:00:47, Johannes Weiner wrote:
> > On Mon, Jan 11, 2016 at 02:07:16PM +0900, Tetsuo Handa wrote:
> > > After the OOM killer is disabled during suspend operation,
> > > any !__GFP_NOFAIL && __GFP_FS allocations are forced to fail.
> > > Thus, any !__GFP_NOFAIL && !__GFP_FS allocations should be
> > > forced to fail as well.
> > > 
> > > Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> > 
> > Why? We had to acknowledge that !__GFP_FS allocations can not fail
> > even when they can't invoke the OOM killer. They are NOFAIL. Just like
> > an explicit __GFP_NOFAIL they should trigger a warning when they occur
> > after the OOM killer has been disabled and then keep looping.
> 
> They are more like GFP_KERNEL than GFP_NOFAIL IMO because unlike
> GFP_NOFAIL they are already allowed to fail due to fatal_signals_pending
> and this has been the case for a really long time.  Even semantically
> they are basically GFP_KERNEL with FS recursion protection in majority
> cases. And I believe that we should allow them to fail long term after
> some FS (btrfs at least) catch up and start handling failures properly.

I see, yeah that's probably a better way to look at it.

Thanks!

Scratch my objection to this patch then. But please do add to/update
that XXX comment above that line, or it'll be confusing. Hm?

			/*
			 * XXX: Page reclaim didn't yield anything,
			 * and the OOM killer can't be invoked, but
			 * keep looping as per tradition. Unless the
			 * system is trying to enter a quiescent state
			 * during suspend and the OOM killer has been
			 * shut off already. Give up like with other
			 * !__GFP_NOFAIL allocations in that case.
			 */
			*did_some_progress = !oom_killer_disabled;

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