linux-kernel - Re: [PATCH] mm, memcg: Add memory.transparent_hugepage

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Date:   Tue, 24 Mar 2020 14:17:36 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     teawater <teawaterz@...ux.alibaba.com>
Cc:     Hui Zhu <teawater@...il.com>, Johannes Weiner <hannes@...xchg.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>, hughd@...gle.com,
        yang.shi@...ux.alibaba.com, kirill@...temov.name,
        dan.j.williams@...el.com, aneesh.kumar@...ux.ibm.com,
        sean.j.christopherson@...el.com, thellstrom@...are.com,
        guro@...com, shakeelb@...gle.com, chris@...isdown.name,
        tj@...nel.org, tglx@...utronix.de, linux-kernel@...r.kernel.org,
        cgroups@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] mm, memcg: Add memory.transparent_hugepage_disabled

On Tue 24-03-20 20:30:32, teawater wrote:
> 
> 
> > 2020年3月24日 19:00，Michal Hocko <mhocko@...nel.org> 写道：
> > 
> > On Tue 24-03-20 18:31:56, Hui Zhu wrote:
> >> /sys/kernel/mm/transparent_hugepage/enabled is the only interface to
> >> control if the application can use THP in system level.
> >> Sometime, we would not want an application use THP even if
> >> transparent_hugepage/enabled is set to "always" or "madvise" because
> >> thp may need more cpu and memory resources in some cases.
> > 
> > Could you specify that sometime by a real usecase in the memcg context
> > please?
> 
> 
> Thanks for your review.
> 
> We use thp+balloon to supply more memory flexibility for vm.
> https://lore.kernel.org/linux-mm/1584893097-12317-1-git-send-email-teawater@gmail.com/
> This is another thread that I am working around thp+balloon.
> 
> Other applications are already deployed on these machines.  The
> transparent_hugepage/enabled is set to never because they used to have
> a lot of THP related performance issues.  And some of them may call
> madvise thp with itself.

If they call madvise then they clearly indicate they prefer THP
regardless the cost. So I really fail to see what memcg specific tuning
brings in.

Could you be more specific about the usecase that cannot work with the
existing THP tuning?
-- 
Michal Hocko
SUSE Labs