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

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Date:   Fri, 22 Jun 2018 11:49:14 -0700 (PDT)
From:   David Rientjes <rientjes@...gle.com>
To:     Michal Hocko <mhocko@...nel.org>
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 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?