linux-kernel - Re: Will the recent memory leak fixes be backported to longterm kernels?

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Message-ID: <20181102154844.GA17619@tower.DHCP.thefacebook.com>
Date:   Fri, 2 Nov 2018 15:48:57 +0000
From:   Roman Gushchin <guro@...com>
To:     Michal Hocko <mhocko@...nel.org>
CC:     Dexuan Cui <decui@...rosoft.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Kernel Team <Kernel-team@...com>,
        "Shakeel Butt" <shakeelb@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Tejun Heo <tj@...nel.org>, Rik van Riel <riel@...riel.com>,
        Konstantin Khlebnikov <koct9i@...il.com>,
        Matthew Wilcox <willy@...radead.org>,
        "Stable@...r.kernel.org" <Stable@...r.kernel.org>
Subject: Re: Will the recent memory leak fixes be backported to longterm
 kernels?

On Fri, Nov 02, 2018 at 09:03:55AM +0100, Michal Hocko wrote:
> On Fri 02-11-18 02:45:42, Dexuan Cui wrote:
> [...]
> > I totally agree. I'm now just wondering if there is any temporary workaround,
> > even if that means we have to run the kernel with some features disabled or
> > with a suboptimal performance?
> 
> One way would be to disable kmem accounting (cgroup.memory=nokmem kernel
> option). That would reduce the memory isolation because quite a lot of
> memory will not be accounted for but the primary source of in-flight and
> hard to reclaim memory will be gone.

In my experience disabling the kmem accounting doesn't really solve the issue
(without patches), but can lower the rate of the leak.

> 
> Another workaround could be to use force_empty knob we have in v1 and
> use it when removing a cgroup. We do not have it in cgroup v2 though.
> The file hasn't been added to v2 because we didn't really have any
> proper usecase. Working around a bug doesn't sound like a _proper_
> usecase but I can imagine workloads that bring a lot of metadata objects
> that are not really interesting for later use so something like a
> targeted drop_caches...

This can help a bit too, but even using the system-wide drop_caches knob
unfortunately doesn't return all the memory back.

Thanks!