From: Michal Hocko <mhocko@suse.com>
To: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>,
Andrew Morton <akpm@linux-foundation.org>,
Dave Hansen <dave.hansen@intel.com>,
Ying Huang <ying.huang@intel.com>,
Dan Williams <dan.j.williams@intel.com>,
David Rientjes <rientjes@google.com>,
Shakeel Butt <shakeelb@google.com>,
linux-mm@kvack.org, cgroups@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH v1 00/11] Manage the top tier memory in a tiered memory
Date: Tue, 6 Apr 2021 11:08:42 +0200 [thread overview]
Message-ID: <YGwlGrHtDJPQF7UG@dhcp22.suse.cz> (raw)
In-Reply-To: <cover.1617642417.git.tim.c.chen@linux.intel.com>
On Mon 05-04-21 10:08:24, Tim Chen wrote:
[...]
> To make fine grain cgroup based management of the precious top tier
> DRAM memory possible, this patchset adds a few new features:
> 1. Provides memory monitors on the amount of top tier memory used per cgroup
> and by the system as a whole.
> 2. Applies soft limits on the top tier memory each cgroup uses
> 3. Enables kswapd to demote top tier pages from cgroup with excess top
> tier memory usages.
Could you be more specific on how this interface is supposed to be used?
> This allows us to provision different amount of top tier memory to each
> cgroup according to the cgroup's latency need.
>
> The patchset is based on cgroup v1 interface. One shortcoming of the v1
> interface is the limit on the cgroup is a soft limit, so a cgroup can
> exceed the limit quite a bit before reclaim before page demotion reins
> it in.
I have to say that I dislike abusing soft limit reclaim for this. In the
past we have learned that the existing implementation is unfixable and
changing the existing semantic impossible due to backward compatibility.
So I would really prefer the soft limit just find its rest rather than
see new potential usecases.
I haven't really looked into details of this patchset but from a cursory
look it seems like you are actually introducing a NUMA aware limits into
memcg that would control consumption from some nodes differently than
other nodes. This would be rather alien concept to the existing memcg
infrastructure IMO. It looks like it is fusing borders between memcg and
cputset controllers.
You also seem to be basing the interface on the very specific usecase.
Can we expect that there will be many different tiers requiring their
own balancing?
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2021-04-06 9:08 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-05 17:08 [RFC PATCH v1 00/11] Manage the top tier memory in a tiered memory Tim Chen
2021-04-05 17:08 ` [RFC PATCH v1 01/11] mm: Define top tier memory node mask Tim Chen
2021-04-05 17:08 ` [RFC PATCH v1 02/11] mm: Add soft memory limit for mem cgroup Tim Chen
2021-04-05 17:08 ` [RFC PATCH v1 03/11] mm: Account the top tier memory usage per cgroup Tim Chen
2021-04-05 17:08 ` [RFC PATCH v1 04/11] mm: Report top tier memory usage in sysfs Tim Chen
2021-04-05 17:08 ` [RFC PATCH v1 05/11] mm: Add soft_limit_top_tier tree for mem cgroup Tim Chen
2021-04-05 17:08 ` [RFC PATCH v1 06/11] mm: Handle top tier memory in cgroup soft limit memory tree utilities Tim Chen
2021-04-05 17:08 ` [RFC PATCH v1 07/11] mm: Account the total top tier memory in use Tim Chen
2021-04-05 17:08 ` [RFC PATCH v1 08/11] mm: Add toptier option for mem_cgroup_soft_limit_reclaim() Tim Chen
2021-04-05 17:08 ` [RFC PATCH v1 09/11] mm: Use kswapd to demote pages when toptier memory is tight Tim Chen
2021-04-05 17:08 ` [RFC PATCH v1 10/11] mm: Set toptier_scale_factor via sysctl Tim Chen
2021-04-05 17:08 ` [RFC PATCH v1 11/11] mm: Wakeup kswapd if toptier memory need soft reclaim Tim Chen
2021-04-06 9:08 ` Michal Hocko [this message]
2021-04-07 22:33 ` [RFC PATCH v1 00/11] Manage the top tier memory in a tiered memory Tim Chen
2021-04-08 11:52 ` Michal Hocko
2021-04-09 23:26 ` Tim Chen
2021-04-12 19:20 ` Shakeel Butt
2021-04-14 8:59 ` Jonathan Cameron
2021-04-15 0:42 ` Tim Chen
2021-04-13 2:15 ` Huang, Ying
2021-04-13 8:33 ` Michal Hocko
2021-04-12 14:03 ` Shakeel Butt
2021-04-08 17:18 ` Shakeel Butt
2021-04-08 18:00 ` Yang Shi
2021-04-08 20:29 ` Shakeel Butt
2021-04-08 20:50 ` Yang Shi
2021-04-12 14:03 ` Shakeel Butt
2021-04-09 7:24 ` Michal Hocko
2021-04-15 22:31 ` Tim Chen
2021-04-16 6:38 ` Michal Hocko
2021-04-14 23:22 ` Tim Chen
2021-04-09 2:58 ` Huang, Ying
2021-04-09 20:50 ` Yang Shi
2021-04-15 22:25 ` Tim Chen
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