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Date:   Tue, 24 Mar 2020 13:23:50 +0000
From:   Chris Down <chris@chrisdown.name>
To:     Hui Zhu <teawater@gmail.com>
Cc:     hannes@cmpxchg.org, mhocko@kernel.org, vdavydov.dev@gmail.com,
        akpm@linux-foundation.org, hughd@google.com,
        yang.shi@linux.alibaba.com, kirill@shutemov.name,
        dan.j.williams@intel.com, aneesh.kumar@linux.ibm.com,
        sean.j.christopherson@intel.com, thellstrom@vmware.com,
        guro@fb.com, shakeelb@google.com, tj@kernel.org,
        tglx@linutronix.de, linux-kernel@vger.kernel.org,
        cgroups@vger.kernel.org, linux-mm@kvack.org,
        Hui Zhu <teawaterz@linux.alibaba.com>
Subject: Re: [PATCH] mm, memcg: Add memory.transparent_hugepage_disabled
Message-ID: <20200324132350.GA7528@chrisdown.name>
References: <1585045916-27339-1-git-send-email-teawater@gmail.com>
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Hui Zhu writes:
>/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.
>
>This commit add a new interface memory.transparent_hugepage_disabled
>in memcg.
>When it set to 1, the application inside the cgroup cannot use THP
>except dax.

I'm against this patch even in the abstract -- this adds an extremely niche use 
case to a general interface, and there are plenty of ways to already indicate 
THP preference.

Perhaps there is some new interface desirable for your use case, but adding a 
new global file to memcg certainly isn't it.