Re: [RFC PATCH] mm, thp: make deferred_split_shrinker memcg-aware

["Kirill A. Shutemov" <kirill@shutemov.name>]

On Thu, Oct 19, 2017 at 01:03:23PM -0700, Neha Agarwal wrote:
> deferred_split_shrinker is NUMA aware. Making it memcg-aware if
> CONFIG_MEMCG is enabled to prevent shrinking memory of memcg(s) that are
> not under memory pressure. This change isolates memory pressure across
> memcgs from deferred_split_shrinker perspective, by not prematurely
> splitting huge pages for the memcg that is not under memory pressure.
> 
> Note that a pte-mapped compound huge page charge is not moved to the dst
> memcg on task migration. Look mem_cgroup_move_charge_pte_range() for
> more information. Thus, mem_cgroup_move_account doesn't get called on
> pte-mapped compound huge pages, hence we do not need to transfer the
> page from source-memcg's split to destinations-memcg's split_queue.
> 
> Tested: Ran two copies of a microbenchmark with partially unmapped
> thp(s) in two separate memory cgroups. When first memory cgroup is put
> under memory pressure, it's own thp(s) split. Other memcg's thp(s)
> remain intact.
> 
> Current implementation is not NUMA aware if MEMCG is compiled. If it is
> important to have this shrinker both NUMA and MEMCG aware, I can work on
> that.  Some feedback on this front will be useful.

I thin, this should be done. That's strange compromise -- memcg vs NUMA.
And I think solving will help a lot with ifdefs.

-- 
 Kirill A. Shutemov

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