Re: [PATCH] mm: fix oom work when memory is under pressure

[Hugh Dickins <hughd@google.com>]

On Sun, 18 Sep 2016, Michal Hocko wrote:
> On Sun 18-09-16 12:04:47, zhong jiang wrote:
> [...]
> >  index 5048083..72dc475 100644
> > --- a/mm/ksm.c
> > +++ b/mm/ksm.c
> > @@ -299,7 +299,7 @@ static inline void free_rmap_item(struct rmap_item *rmap_item)
> > 
> >  static inline struct stable_node *alloc_stable_node(void)
> >  {
> > -       return kmem_cache_alloc(stable_node_cache, GFP_KERNEL);
> > +       return kmem_cache_alloc(stable_node_cache, __GFP_HIGH);
> >  }
> 
> I do not want to speak for Hugh but I believe he meant something
> different. The above will grant access to memory reserves but it doesn't
> wake kswapd nor the direct reclaim. I guess he meant GFP_KERNEL | __GFP_HIGH

You speak for me correctly, Michal: sorry I wasn't clear, Zhongjiang, yes,
I meant __GFP_HIGH as a modifier for GFP_KERNEL: GFP_KERNEL | __GFP_HIGH

And after running it past Michal and thinking on it some more, I do
still think that it's the right thing to do for alloc_stable_node().
But please only include that change in your patch if you yourself are
comfortable with it: it is very definitely a much lower order issue
than the alloc_rmap_item() issue, and can always be added later.

(I have no view on whether and how this problem still occurs with
OOM reaper: I leave the thinking on that to you and the experts.)

Hugh

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