linux-kernel - Re: [PATCH v2] mm/balloon_compaction: Informative allocation warnings

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Message-ID: <9DDD9A0D-C88C-4EEF-A41B-E5646BDEF414@vmware.com>
Date:   Wed, 21 Aug 2019 19:19:18 +0000
From:   Nadav Amit <namit@...are.com>
To:     David Hildenbrand <david@...hat.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 <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] mm/balloon_compaction: Informative allocation warnings

> On Aug 21, 2019, at 12:12 PM, David Hildenbrand <david@...hat.com> wrote:
> 
> On 21.08.19 21:10, Nadav Amit wrote:
>>> On Aug 21, 2019, at 12:06 PM, David Hildenbrand <david@...hat.com> wrote:
>>> 
>>> On 21.08.19 20:59, Nadav Amit wrote:
>>>>> On Aug 21, 2019, at 11:57 AM, David Hildenbrand <david@...hat.com> wrote:
>>>>> 
>>>>> On 21.08.19 11:41, Nadav Amit wrote:
>>>>>> There is no reason to print generic warnings when balloon memory
>>>>>> allocation fails, as failures 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.
>>>>>> 
>>>>>> Since such warnings can still be useful to indicate that the balloon is
>>>>>> over-inflated, print more informative and less frightening warning if
>>>>>> allocation fails instead.
>>>>>> 
>>>>>> Cc: David Hildenbrand <david@...hat.com>
>>>>>> Cc: Jason Wang <jasowang@...hat.com>
>>>>>> Signed-off-by: Nadav Amit <namit@...are.com>
>>>>>> 
>>>>>> ---
>>>>>> 
>>>>>> v1->v2:
>>>>>> * Print informative warnings instead suppressing [David]
>>>>>> ---
>>>>>> mm/balloon_compaction.c | 7 ++++++-
>>>>>> 1 file changed, 6 insertions(+), 1 deletion(-)
>>>>>> 
>>>>>> diff --git a/mm/balloon_compaction.c b/mm/balloon_compaction.c
>>>>>> index 798275a51887..0c1d1f7689f0 100644
>>>>>> --- a/mm/balloon_compaction.c
>>>>>> +++ b/mm/balloon_compaction.c
>>>>>> @@ -124,7 +124,12 @@ EXPORT_SYMBOL_GPL(balloon_page_list_dequeue);
>>>>>> struct page *balloon_page_alloc(void)
>>>>>> {
>>>>>> 	struct page *page = alloc_page(balloon_mapping_gfp_mask() |
>>>>>> -				       __GFP_NOMEMALLOC | __GFP_NORETRY);
>>>>>> +				       __GFP_NOMEMALLOC | __GFP_NORETRY |
>>>>>> +				       __GFP_NOWARN);
>>>>>> +
>>>>>> +	if (!page)
>>>>>> +		pr_warn_ratelimited("memory balloon: memory allocation failed");
>>>>>> +
>>>>>> 	return page;
>>>>>> }
>>>>>> EXPORT_SYMBOL_GPL(balloon_page_alloc);
>>>>> 
>>>>> Not sure if "memory balloon" is the right wording. hmmm.
>>>>> 
>>>>> Acked-by: David Hildenbrand <david@...hat.com>
>>>> 
>>>> Do you have a better suggestion?
>>> 
>>> Not really - that's why I ack'ed :)
>>> 
>>> However, thinking about it - what about moving the check + print to the
>>> caller and then using dev_warn... or sth. like simple "virtio_balloon:
>>> ..." ? You can then drop the warning for vmware balloon if you feel like
>>> not needing it.
>> 
>> Actually, there is already a warning that is printed by the virtue_balloon
>> in fill_balloon():
>> 
>>                struct page *page = balloon_page_alloc();
>> 
>>                if (!page) {
>>                        dev_info_ratelimited(&vb->vdev->dev,
>>                                             "Out of puff! Can't get %u pages\n",
>>                                             VIRTIO_BALLOON_PAGES_PER_PAGE);
>>                        /* Sleep for at least 1/5 of a second before retry. */
>>                        msleep(200);
>>                        break;
>>                }
>> 
>> So are you ok with going back to v1?
> 
> Whoops, I missed that - sorry - usually the warnings scream louder at me :D
> 
> Yes, v1 is fine with me!

Thanks, I missed this one too. This change should prevent making users
concerned for no good reason.