Messages in this thread | | | From | KOSAKI Motohiro <> | Subject | Re: [PATCH 4/4] Memory controller soft limit reclaim on contention (v3) | Date | Wed, 4 Mar 2009 09:07:21 +0900 (JST) |
| |
Hi Balbir
> > > > kswapd's roll is increasing free pages until zone->pages_high in "own node". > > > > mem_cgroup_soft_limit_reclaim() free one (or more) exceed page in any node. > > > > > > > > Oh, well. > > > > I think it is not consistency. > > > > > > > > if mem_cgroup_soft_limit_reclaim() is aware to target node and its pages_high, > > > > I'm glad. > > > > > > Yes, correct the role of kswapd is to keep increasing free pages until > > > zone->pages_high and the first set of pages to consider is the memory > > > controller over their soft limits. We pass the zonelist to ensure that > > > while doing soft reclaim, we focus on the zonelist associated with the > > > node. Kamezawa had concernes over calling the soft limit reclaim from > > > __alloc_pages_internal(), did you prefer that call path? > > > > I read your patch again. > > So, mem_cgroup_soft_limit_reclaim() caller place seems in balance_pgdat() is better. > > > > Please imazine most bad scenario. > > CPU0 (kswapd) take to continue shrinking. > > CPU1 take another activity and charge memcg conteniously. > > At that time, balance_pgdat() don't exit very long time. then > > mem_cgroup_soft_limit_reclaim() is never called. > > > > Yes, true... that is why I added the hooks in __alloc_pages_internal() > in the first two revisions, but Kamezawa objected to them. In the > scenario that you mention that balance_pgdat() is busy, if we are > under global system memory pressure, even after freeing memory from > soft limited cgroups, we don't have sufficient free memory. We need to > go reclaim from the whole system. An administrator can easily avoid > the above scenario by using hard limits on the cgroup running on CPU1.
I agree with soft limit implementation is difficult.
but I still don't like soft limit in __alloc_pages_internal(). if it does, kswapd reclaim the pages from global LRU *before* shrinking soft limit.
again, linux reclaim policy is
free < pages_low: run kswapd free < pages_min: foreground reclaim via __alloc_pages_internal()
then, if soft limit reclaim put into __alloc_pages_internal(),
free < pages_low: run kswapd free < pages_min: soft limit reclaim and foreground reclaim via __alloc_pages_internal()
it seems unintetional behavior.
In addition, I still strongly oppose againt global lock although soft limit shrinking don't put into __alloc_pages_internal(). I think it doesn't depend on caller place.
| |