linux-kernel - Re: [PATCH v1] kernel/trace:check the val against the available mem

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Message-ID: <20180405142749.GL6312@dhcp22.suse.cz>
Date:   Thu, 5 Apr 2018 16:27:49 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Joel Fernandes <joelaf@...gle.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Zhaoyang Huang <huangzhaoyang@...il.com>,
        Ingo Molnar <mingo@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        kernel-patch-test@...ts.linaro.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        "open list:MEMORY MANAGEMENT" <linux-mm@...ck.org>,
        Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH v1] kernel/trace:check the val against the available mem

On Thu 05-04-18 07:22:58, Matthew Wilcox wrote:
> On Wed, Apr 04, 2018 at 09:12:52PM -0700, Joel Fernandes wrote:
> > On Wed, Apr 4, 2018 at 7:58 PM, Matthew Wilcox <willy@...radead.org> wrote:
> > > On Wed, Apr 04, 2018 at 11:47:30AM -0400, Steven Rostedt wrote:
> > >> I originally was going to remove the RETRY_MAYFAIL, but adding this
> > >> check (at the end of the loop though) appears to have OOM consistently
> > >> kill this task.
> > >>
> > >> I still like to keep RETRY_MAYFAIL, because it wont trigger OOM if
> > >> nothing comes in and tries to do an allocation, but instead will fail
> > >> nicely with -ENOMEM.
> > >
> > > I still don't get why you want RETRY_MAYFAIL.  You know that tries
> > > *harder* to allocate memory than plain GFP_KERNEL does, right?  And
> > > that seems like the exact opposite of what you want.
> > 
> > No. We do want it to try harder but not if its already setup for failure.
> 
> I understand you don't want GFP_NORETRY.  But why is it more important for
> this allocation to succeed than other normal GFP_KERNEL allocations?

I guess they simply want a failure rather than OOM even when they can
shoot themselves into head by using oom_origin. It is still quite ugly
to see OOM report...

-- 
Michal Hocko
SUSE Labs