From: Kirill Tkhai <ktkhai@virtuozzo.com>
To: Michal Hocko <mhocko@kernel.org>
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 14:05:28 +0300 [thread overview]
Message-ID: <9bd4044b-63d0-b24f-a108-3061c00ed131@virtuozzo.com> (raw)
In-Reply-To: <20190123110254.GU4087@dhcp22.suse.cz>
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?
Kirill
next prev parent reply other threads:[~2019-01-23 11:05 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 [this message]
2019-01-23 12:10 ` Michal Hocko
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