On Thu, 28 Sep 2017 10:48:55 +0300 Kirill Tkhai <ktk...@virtuozzo.com> wrote:
> >> This patch aims to make super_cache_count() (and other functions, > >> which count LRU nr_items) more effective. > >> It allows list_lru_node::memcg_lrus to be RCU-accessed, and makes > >> __list_lru_count_one() count nr_items lockless to minimize > >> overhead introduced by locking operation, and to make parallel > >> reclaims more scalable. > > > > And... what were the effects of the patch? Did you not run the same > > performance tests after applying it? > > I've just detected the such high usage of shrink slab on production node. > It's rather > difficult to make it use another kernel, than it uses, only kpatches are > possible. > So, I haven't estimated how it acts on node's performance. > On test node I see, that the patch obviously removes raw_spin_lock from perf > profile. > So, it's a little bit untested in this way. Well that's a problem. The patch increases list_lru.o text size by a lot (4800->5696) which will have a cost. And we don't have proof that any benefit is worth that cost. It shouldn't be too hard to cook up a synthetic test to trigger memcg slab reclaim and then run a before-n-after benchmark?
