[Sorry for a late reply]

On Fri 24-06-16 13:51:01, Johannes Weiner wrote:

This is a rebased version on top of mmots sans the nodelru stuff.

---

23047a96d7cf ("mm: workingset: per-cgroup cache thrash detection")
added a page->mem_cgroup lookup to the cache eviction, refault, and
activation paths, as well as locking to the activation path, and the
vm-scalability tests showed a regression of -23%. While the test in
question is an artificial worst-case scenario that doesn't occur in
real workloads - reading two sparse files in parallel at full CPU
speed just to hammer the LRU paths - there is still some optimizations
that can be done in those paths.

Inline the lookup functions to eliminate calls. Also, page->mem_cgroup
doesn't need to be stabilized when counting an activation; we merely
need to hold the RCU lock to prevent the memcg from being freed.

This cuts down on overhead quite a bit:

23047a96d7cfcfca 063f6715e77a7be5770d6081fe
---------------- --------------------------
         %stddev     %change         %stddev
             \          |                \
  21621405 +- 0%     +11.3%   24069657 +- 2%  vm-scalability.throughput

Reported-by: Ye Xiaolong <redacted>
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>

Acked-by: Michal Hocko <mhocko@suse.com>

Minor note below

+static inline struct mem_cgroup *page_memcg_rcu(struct page *page)
+{

I guess rcu_read_lock_held() here would be appropriate

+	return READ_ONCE(page->mem_cgroup);
+}

-- 
Michal Hocko
SUSE Labs

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