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

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Date:   Wed, 21 Aug 2019 19:44:33 +0000
From:   Nadav Amit <namit@...are.com>
To:     "Michael S. Tsirkin" <mst@...hat.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 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