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

From: Michal Hocko <mhocko@kernel.org>
To: Matthew Wilcox <willy@infradead.org>
Cc: Joel Fernandes <joelaf@google.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Zhaoyang Huang <huangzhaoyang@gmail.com>,
	Ingo Molnar <mingo@kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	kernel-patch-test@lists.linaro.org,
	Andrew Morton <akpm@linux-foundation.org>,
	"open list:MEMORY MANAGEMENT" <linux-mm@kvack.org>,
	Vlastimil Babka <vbabka@suse.cz>
Subject: Re: [PATCH v1] kernel/trace:check the val against the available mem
Date: Thu, 5 Apr 2018 16:27:49 +0200	[thread overview]
Message-ID: <20180405142749.GL6312@dhcp22.suse.cz> (raw)
In-Reply-To: <20180405142258.GA28128@bombadil.infradead.org>

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@infradead.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