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

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Date:   Wed, 21 Aug 2019 21:13:36 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Nadav Amit <namit@...are.com>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        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>
Subject: Re: [PATCH] mm/balloon_compaction: suppress allocation warnings

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>

-- 

Thanks,

David / dhildenb