[PATCH] mm: memcg: make sure memory.events is uptodate when waking pollers

[Johannes Weiner]

On Wed, Apr 04, 2018 at 09:58:29AM -0700, Tejun Heo wrote:
> On Wed, Apr 04, 2018 at 04:34:47PM +0200, Michal Hocko wrote:
> > > > The lazy updates are neat, but I'm a little concerned at the memory
> > > > footprint. On a 64-cpu machine for example, this adds close to 9000
> > > > words to struct mem_cgroup. And we really only need the accuracy for
> > > > the 4 cgroup items in memory.events, not all VM events and stats.
> > > > 
> > > > Why not restrict the patch to those? It would also get rid of the
> > > > weird sharing between VM and cgroup enums.
> > > 
> > > In fact, I wonder if we need per-cpuness for MEMCG_LOW, MEMCG_HIGH
> > > etc. in the first place. They describe super high-level reclaim and
> > > OOM events, so they're not nearly as hot as other VM events and
> > > stats. We could probably just have a per-memcg array of atomics.
> > 
> > Agreed!
> 
> Ah, yeah, if we aren't worried about the update frequency of
> MEMCG_HIGH, which likely is the highest freq, we can just switch to
> atomic_t.  I'm gonna apply the cgroup stat refactoring patches to
> cgroup, so if we ever wanna switch the counter to rstat, we can easily
> do that later.

Yeah, that's still great to have as generalized infrastructure.

For memory.events, how about this instead?

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