linux-kernel - Re: [PATCH 4.14 108/159] kvm, mm: account kvm related kmem slabs to kmemcg

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Date:   Fri, 22 Dec 2017 14:06:07 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Shakeel Butt <shakeelb@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sasha Levin <alexander.levin@...izon.com>
Subject: Re: [PATCH 4.14 108/159] kvm, mm: account kvm related kmem slabs to
 kmemcg

On Fri 22-12-17 13:41:22, Greg KH wrote:
> On Fri, Dec 22, 2017 at 10:34:07AM +0100, Michal Hocko wrote:
> > On Fri 22-12-17 09:46:33, Greg KH wrote:
> > > 4.14-stable review patch.  If anyone has any objections, please let me know.
> > > 
> > > ------------------
> > > 
> > > From: Shakeel Butt <shakeelb@...gle.com>
> > > 
> > > 
> > > [ Upstream commit 46bea48ac241fe0b413805952dda74dd0c09ba8b ]
> > > 
> > > The kvm slabs can consume a significant amount of system memory
> > > and indeed in our production environment we have observed that
> > > a lot of machines are spending significant amount of memory that
> > > can not be left as system memory overhead. Also the allocations
> > > from these slabs can be triggered directly by user space applications
> > > which has access to kvm and thus a buggy application can leak
> > > such memory. So, these caches should be accounted to kmemcg.
> > > 
> > > Signed-off-by: Shakeel Butt <shakeelb@...gle.com>
> > > Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> > > Signed-off-by: Sasha Levin <alexander.levin@...izon.com>
> > > Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > 
> > The patch is not marked for stable, neither it fixes an existing bug.
> > It is a nice to have thing for sure but I am wondering how this got
> > through stable-filter. 
> 
> Sasha picked it out, and it seemed like a sane thing to backport.  If
> you think it's not worthy, I'll gladly drop it, but it seemed like such
> a simple bugfix to include.

It is not that I would have some specific concerns about this particular
patch. It is more of a worry about the overal process. I thought that
_any_ patch backported to the stable tree would require a specific bug
to be fixed or in exceptional cases a performance issue. I have
experienced this pushback myself when trying to push "no real bug report
but better to have this plugged" patches.

So something has apparently changed in the process, I just haven't
noticed it. I am worried this might lead to more regression in future.
Not that my worry counts all that much as I am not a stable kernel user
though. So this is just my 2c worth of worry.
-- 
Michal Hocko
SUSE Labs