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Date:   Tue, 23 Jan 2018 12:39:12 +0100
From:   Michal Hocko <mhocko@kernel.org>
To:     Christian =?iso-8859-1?Q?K=F6nig?= <christian.koenig@amd.com>
Cc:     Eric Anholt <eric@anholt.net>,
        Andrey Grodzovsky <andrey.grodzovsky@amd.com>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        dri-devel@lists.freedesktop.org, amd-gfx@lists.freedesktop.org
Subject: Re: [RFC] Per file OOM badness
Message-ID: <20180123113912.GH1526@dhcp22.suse.cz>
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On Fri 19-01-18 17:54:36, Christian K?nig wrote:
> Am 19.01.2018 um 13:20 schrieb Michal Hocko:
> > On Fri 19-01-18 13:13:51, Michal Hocko wrote:
> > > On Fri 19-01-18 12:37:51, Christian K?nig wrote:
> > > [...]
> > > > The per file descriptor badness is/was just the much easier approach to
> > > > solve the issue, because the drivers already knew which client is currently
> > > > using which buffer objects.
> > > > 
> > > > I of course agree that file descriptors can be shared between processes and
> > > > are by themselves not killable. But at least for our graphics driven use
> > > > case I don't see much of a problem killing all processes when a file
> > > > descriptor is used by more than one at the same time.
> > > Ohh, I absolutely see why you have chosen this way for your particular
> > > usecase. I am just arguing that this would rather be more generic to be
> > > merged. If there is absolutely no other way around we can consider it
> > > but right now I do not see that all other options have been considered
> > > properly. Especially when the fd based approach is basically wrong for
> > > almost anybody else.
> > And more importantly. Iterating over _all_ fd which is what is your
> > approach is based on AFAIU is not acceptable for the OOM path. Even
> > though oom_badness is not a hot path we do not really want it to take a
> > lot of time either. Even the current iteration over all processes is
> > quite time consuming. Now you want to add the number of opened files and
> > that might be quite many per process.
> 
> Mhm, crap that is a really good argument.
> 
> How about adding a linked list of callbacks to check for the OOM killer to
> check for each process?
> 
> This way we can avoid finding the process where we need to account things on
> when memory is allocated and still allow the OOM killer to only check the
> specific callbacks it needs to determine the score of a process?

I might be oversimplifying but there really have to be a boundary when
you have the target user context, no? Then do the accounting when you
get data to the user.
-- 
Michal Hocko
SUSE Labs