Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
In-Reply-To: <20171117155509.GA920@castle>
References: <1510888199-5886-1-git-send-email-laoar.shao@gmail.com>
 <CALvZod7AY=J3i0NL-VuWWOxjdVmWh7VnpcQhdx7+Jt-Hnqrk+g@mail.gmail.com> <20171117155509.GA920@castle>
From:   Yafang Shao <laoar.shao@gmail.com>
Date:   Sat, 18 Nov 2017 00:20:40 +0800
Message-ID: <CALOAHbAWvYKve4eB9+zissgi24cNKeFih1=avfSi_dH5upQVOg@mail.gmail.com>
Subject: Re: [PATCH] mm/shmem: set default tmpfs size according to memcg limit
To:     Roman Gushchin <guro@fb.com>
Cc:     Shakeel Butt <shakeelb@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        Michal Hocko <mhocko@suse.com>, Tejun Heo <tj@kernel.org>,
        khlebnikov@yandex-team.ru, mka@chromium.org,
        Hugh Dickins <hughd@google.com>,
        Cgroups <cgroups@vger.kernel.org>, Linux MM <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

2017-11-17 23:55 GMT+08:00 Roman Gushchin <guro@fb.com>:
> On Thu, Nov 16, 2017 at 08:43:17PM -0800, Shakeel Butt wrote:
>> On Thu, Nov 16, 2017 at 7:09 PM, Yafang Shao <laoar.shao@gmail.com> wrote:
>> > Currently the default tmpfs size is totalram_pages / 2 if mount tmpfs
>> > without "-o size=XXX".
>> > When we mount tmpfs in a container(i.e. docker), it is also
>> > totalram_pages / 2 regardless of the memory limit on this container.
>> > That may easily cause OOM if tmpfs occupied too much memory when swap is
>> > off.
>> > So when we mount tmpfs in a memcg, the default size should be limited by
>> > the memcg memory.limit.
>> >
>>
>> The pages of the tmpfs files are charged to the memcg of allocators
>> which can be in memcg different from the memcg in which the mount
>> operation happened. So, tying the size of a tmpfs mount where it was
>> mounted does not make much sense.
>
> Also, memory limit is adjustable,

Yes. But that's irrelevant.

> and using a particular limit value
> at a moment of tmpfs mounting doesn't provide any warranties further.
>

I can not agree.
The default size of tmpfs is totalram / 2, the reason we do this is to
provide any warranties further IMHO.

> Is there a reason why the userspace app which is mounting tmpfs can't
> set the size based on memory.limit?

That's because of misuse.
The application should set size with "-o size=" when mount tmpfs, but
not all applications do this.
As we can't guarantee that all applications will do this, we should
give them a proper default value.

Thanks
Yafang

From 1584347340232132320@xxx Fri Nov 17 20:42:46 +0000 2017
X-GM-THRID: 1584307723039976913
X-Gmail-Labels: Inbox,Category Forums,HistoricalUnread