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

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Date:   Thu, 5 Apr 2018 07:22:58 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Joel Fernandes <joelaf@...gle.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Michal Hocko <mhocko@...nel.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 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?