linux-kernel - Re: [patch] mm, oom: fix unnecessary killing of additional processes

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Date:   Mon, 25 Jun 2018 11:04:34 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     David Rientjes <rientjes@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [patch] mm, oom: fix unnecessary killing of additional processes

On Fri 22-06-18 11:49:14, David Rientjes wrote:
> On Fri, 22 Jun 2018, Michal Hocko wrote:
> 
> > > > preempt_disable() is required because it calls kvm_kick_many_cpus() with 
> > > > wait == true because KVM_REQ_APIC_PAGE_RELOAD sets KVM_REQUEST_WAIT and 
> > > > thus the smp_call_function_many() is going to block until all cpus can run 
> > > > ack_flush().
> > > 
> > > I will make sure to talk to the maintainer of the respective code to
> > > do the nonblock case correctly.
> > 
> > I've just double checked this particular code and the wait path and this
> > one is not a sleep. It is a busy wait for IPI to get handled. So this
> > one should be OK AFAICS. Anyway I will send an RFC and involve
> > respective maintainers to make sure I am not making any incorrect
> > assumptions.
> 
> Do you believe that having the only potential source of memory freeing 
> busy waiting for all other cpus on the system to run ack_flush() is 
> particularly dangerous given the fact that they may be allocating 
> themselves?

These are IPIs. How could they depend on a memory allocation? In other
words we do rely on the very same mechanism for TLB flushing so this is
any different.

Maybe I am missing something here though.

-- 
Michal Hocko
SUSE Labs