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 12:02:54 +0100 [thread overview]
Message-ID: <20190123110254.GU4087@dhcp22.suse.cz> (raw)
In-Reply-To: <fa1d9a1f-99c8-a4ae-da7f-ed90336497e9@virtuozzo.com>
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?
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2019-01-23 11:02 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 [this message]
2019-01-23 11:05 ` Kirill Tkhai
2019-01-23 12:10 ` Michal Hocko
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