linux-kernel - Re: [PATCH] mm/balloon_compaction: suppress allocation warnings

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Date:   Wed, 4 Sep 2019 06:37:15 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Nadav Amit <namit@...are.com>
Cc:     Jason Wang <jasowang@...hat.com>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        David Hildenbrand <david@...hat.com>
Subject: Re: [PATCH] mm/balloon_compaction: suppress allocation warnings

On Wed, Aug 21, 2019 at 07:44:33PM +0000, Nadav Amit wrote:
> > On Aug 21, 2019, at 12:13 PM, David Hildenbrand <david@...hat.com> wrote:
> > 
> > On 21.08.19 18:34, Nadav Amit wrote:
> >>> On Aug 21, 2019, at 9:29 AM, David Hildenbrand <david@...hat.com> wrote:
> >>> 
> >>> On 21.08.19 18:23, Nadav Amit wrote:
> >>>>> On Aug 21, 2019, at 9:05 AM, David Hildenbrand <david@...hat.com> wrote:
> >>>>> 
> >>>>> On 20.08.19 11:16, Nadav Amit wrote:
> >>>>>> There is no reason to print warnings when balloon page allocation fails,
> >>>>>> as they are expected and can be handled gracefully.  Since VMware
> >>>>>> balloon now uses balloon-compaction infrastructure, and suppressed these
> >>>>>> warnings before, it is also beneficial to suppress these warnings to
> >>>>>> keep the same behavior that the balloon had before.
> >>>>> 
> >>>>> I am not sure if that's a good idea. The allocation warnings are usually
> >>>>> the only trace of "the user/admin did something bad because he/she tried
> >>>>> to inflate the balloon to an unsafe value". Believe me, I processed a
> >>>>> couple of such bugreports related to virtio-balloon and the warning were
> >>>>> very helpful for that.
> >>>> 
> >>>> Ok, so a message is needed, but does it have to be a generic frightening
> >>>> warning?
> >>>> 
> >>>> How about using __GFP_NOWARN, and if allocation do something like:
> >>>> 
> >>>> pr_warn(“Balloon memory allocation failed”);
> >>>> 
> >>>> Or even something more informative? This would surely be less intimidating
> >>>> for common users.
> >>> 
> >>> ratelimit would make sense :)
> >>> 
> >>> And yes, this would certainly be nicer.
> >> 
> >> Thanks. I will post v2 of the patch.
> > 
> > As discussed in v2, we already print a warning in virtio-balloon, so I
> > am fine with this patch.
> > 
> > Reviewed-by: David Hildenbrand <david@...hat.com>
> 
> Michael,
> 
> If it is possible to get it to 5.3, to avoid behavioral change for VMware
> balloon users, it would be great.
> 
> Thanks,
> Nadav

Just back from vacation, I'll try.