linux-kernel - Re: [PATCH] mm/shmem: set default tmpfs size according to memcg limit

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Sat, 18 Nov 2017 00:20:40 +0800
From:   Yafang Shao <laoar.shao@...il.com>
To:     Roman Gushchin <guro@...com>
Cc:     Shakeel Butt <shakeelb@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Michal Hocko <mhocko@...e.com>, Tejun Heo <tj@...nel.org>,
        khlebnikov@...dex-team.ru, mka@...omium.org,
        Hugh Dickins <hughd@...gle.com>,
        Cgroups <cgroups@...r.kernel.org>, Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm/shmem: set default tmpfs size according to memcg limit

2017-11-17 23:55 GMT+08:00 Roman Gushchin <guro@...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@...il.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