From: Michal Hocko <mhocko@kernel.org>
To: Kirill Tkhai <ktkhai@virtuozzo.com>
Cc: Yang Shi <yang.shi@linux.alibaba.com>,
hannes@cmpxchg.org, akpm@linux-foundation.org,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH] mm: vmscan: do not iterate all mem cgroups for global direct reclaim
Date: Wed, 23 Jan 2019 13:10:58 +0100 [thread overview]
Message-ID: <20190123121058.GW4087@dhcp22.suse.cz> (raw)
In-Reply-To: <9bd4044b-63d0-b24f-a108-3061c00ed131@virtuozzo.com>
On Wed 23-01-19 14:05:28, Kirill Tkhai wrote:
> On 23.01.2019 14:02, Michal Hocko wrote:
> > On Wed 23-01-19 13:28:03, Kirill Tkhai wrote:
> >> On 22.01.2019 23:09, Yang Shi wrote:
> >>> In current implementation, both kswapd and direct reclaim has to iterate
> >>> all mem cgroups. It is not a problem before offline mem cgroups could
> >>> be iterated. But, currently with iterating offline mem cgroups, it
> >>> could be very time consuming. In our workloads, we saw over 400K mem
> >>> cgroups accumulated in some cases, only a few hundred are online memcgs.
> >>> Although kswapd could help out to reduce the number of memcgs, direct
> >>> reclaim still get hit with iterating a number of offline memcgs in some
> >>> cases. We experienced the responsiveness problems due to this
> >>> occassionally.
> >>>
> >>> Here just break the iteration once it reclaims enough pages as what
> >>> memcg direct reclaim does. This may hurt the fairness among memcgs
> >>> since direct reclaim may awlays do reclaim from same memcgs. But, it
> >>> sounds ok since direct reclaim just tries to reclaim SWAP_CLUSTER_MAX
> >>> pages and memcgs can be protected by min/low.
> >>
> >> In case of we stop after SWAP_CLUSTER_MAX pages are reclaimed; it's possible
> >> the following situation. Memcgs, which are closest to root_mem_cgroup, will
> >> become empty, and you will have to iterate over empty memcg hierarchy long time,
> >> just to find a not empty memcg.
> >>
> >> I'd suggest, we should not lose fairness. We may introduce
> >> mem_cgroup::last_reclaim_child parameter to save a child
> >> (or its id), where the last reclaim was interrupted. Then
> >> next reclaim should start from this child:
> >
> > Why is not our reclaim_cookie based caching sufficient?
>
> Hm, maybe I missed them. Do cookies already implement this functionality?
Have a look at mem_cgroup_iter
--
Michal Hocko
SUSE Labs
prev parent reply other threads:[~2019-01-23 12:11 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-22 20:09 Yang Shi
2019-01-23 9:59 ` Michal Hocko
2019-01-23 20:24 ` Yang Shi
2019-01-24 8:43 ` Michal Hocko
2019-01-26 1:42 ` Yang Shi
2019-01-23 10:28 ` Kirill Tkhai
2019-01-23 11:02 ` Michal Hocko
2019-01-23 11:05 ` Kirill Tkhai
2019-01-23 12:10 ` Michal Hocko [this message]
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