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

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Message-ID: <36AC2460-9E88-4BAF-B793-A14A00E41617@vmware.com>
Date:   Wed, 21 Aug 2019 19:10:28 +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 12:06 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?