From: David Hildenbrand <david@redhat.com>
To: Minchan Kim <minchan@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>,
Andrew Morton <akpm@linux-foundation.org>,
linux-mm <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>,
joaodias@google.com
Subject: Re: [PATCH] mm: be more verbose for alloc_contig_range faliures
Date: Thu, 18 Feb 2021 17:53:22 +0100 [thread overview]
Message-ID: <694c1d6a-d3bc-71ec-7730-e83714e85c25@redhat.com> (raw)
In-Reply-To: <YC6aIL67PaYlmeYq@google.com>
On 18.02.21 17:47, Minchan Kim wrote:
> On Thu, Feb 18, 2021 at 05:26:08PM +0100, David Hildenbrand wrote:
>> On 18.02.21 17:19, Minchan Kim wrote:
>>> On Thu, Feb 18, 2021 at 10:43:21AM +0100, David Hildenbrand wrote:
>>>> On 18.02.21 10:35, Michal Hocko wrote:
>>>>> On Thu 18-02-21 10:02:43, David Hildenbrand wrote:
>>>>>> On 18.02.21 09:56, Michal Hocko wrote:
>>>>>>> On Wed 17-02-21 08:36:03, Minchan Kim wrote:
>>>>>>>> alloc_contig_range is usually used on cma area or movable zone.
>>>>>>>> It's critical if the page migration fails on those areas so
>>>>>>>> dump more debugging message like memory_hotplug unless user
>>>>>>>> specifiy __GFP_NOWARN.
>>>>>>>
>>>>>>> I agree with David that this has a potential to generate a lot of output
>>>>>>> and it is not really clear whether it is worth it. Page isolation code
>>>>>>> already has REPORT_FAILURE mode which currently used only for the memory
>>>>>>> hotplug because this was just too noisy from the CMA path - d381c54760dc
>>>>>>> ("mm: only report isolation failures when offlining memory").
>>>>>>>
>>>>>>> Maybe migration failures are less likely to fail but still.
>>>>>>
>>>>>> Side note: I really dislike that uncontrolled error reporting on memory
>>>>>> offlining path we have enabled as default. Yeah, it might be useful for
>>>>>> ZONE_MOVABLE in some cases, but otherwise it's just noise.
>>>>>>
>>>>>> Just do a "sudo stress-ng --memhotplug 1" and see the log getting flooded
>>>>>
>>>>> Anyway we can discuss this in a separate thread but I think this is not
>>>>> a representative workload.
>>>>
>>>> Sure, but the essence is "this is noise", and we'll have more noise on
>>>> alloc_contig_range() as we see these calls more frequently. There should be
>>>> an explicit way to enable such *debug* messages.
>>>
>>> alloc_contig_range already has gfp_mask and it respects __GFP_NOWARN.
>>
>> I am not 100% sure it does.
>
> Oh, it should. Otherwise, let's fix either of caller or
> alloc_contig_range since we have a customer.
>
> ```
> ret = alloc_contig_range(pfn, pfn + count, MIGRATE_CMA,
> GFP_KERNEL | (no_warn ? __GFP_NOWARN : 0))
> ```
>
Oh, interesting. So I certainly want to add that for virtio-mem as well
- thanks.
And discussed, we should hide the one pr_info... in alloc_contig_range()
as well.
>>
>>> Why shouldn't people use it if they don't care the failure?
>>
>> Because flooding the log with noise maybe a handful of people on this planet
>> care about is absolutely useless. With the warnings in warn_alloc() people
>> can at least conclude something reasonable.
>>
>>> Semantically, it makes sense to me.
>>>
>>> About the messeage flooding, shouldn't we go with ratelimiting?
>>
>> At least that (see warn_alloc()). But I'd even want to see some other
>> trigger to enable this explicitly on demand.
>
> No objection.
>
> How about adding verbose knob under CONFIG_CMA_DEBUGFS with
> alloc_contig_range(..., bool verbose) like start_isolate_page_range?
>
> If admin turns on the verbose mode under CONFIG_CMA_DEBUGFS,
> cma_alloc will pass alloc_contig_range(...., true).
I'd handle this internally in alloc_contig_range and not pass magic
flags around. Some kind of debug knob to enable advanced messages
(exceeding the usual allocation warnings we would usually see).
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2021-02-18 16:53 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-17 16:36 [PATCH] mm: be more verbose for alloc_contig_range faliures Minchan Kim
2021-02-17 16:51 ` David Hildenbrand
2021-02-17 17:26 ` Minchan Kim
2021-02-17 17:34 ` David Hildenbrand
2021-02-17 17:45 ` Minchan Kim
2021-02-18 8:56 ` Michal Hocko
2021-02-18 9:02 ` David Hildenbrand
2021-02-18 9:35 ` Michal Hocko
2021-02-18 9:43 ` David Hildenbrand
2021-02-18 9:59 ` Michal Hocko
2021-02-18 16:19 ` Minchan Kim
2021-02-18 16:26 ` David Hildenbrand
2021-02-18 16:47 ` Minchan Kim
2021-02-18 16:53 ` David Hildenbrand [this message]
2021-02-19 9:28 ` Michal Hocko
2021-02-19 9:30 ` David Hildenbrand
2021-02-19 10:02 ` Michal Hocko
2021-02-19 10:34 ` David Hildenbrand
[not found] ` <YD50pcPuwV456vwm@google.com>
2021-03-04 16:01 ` Minchan Kim
2021-03-04 16:10 ` David Hildenbrand
2021-03-04 16:23 ` Minchan Kim
2021-03-04 16:28 ` David Hildenbrand
2021-03-04 17:11 ` Minchan Kim
2021-03-04 17:23 ` David Hildenbrand
2021-03-04 18:11 ` Minchan Kim
2021-03-04 18:22 ` Minchan Kim
2021-03-08 12:49 ` Michal Hocko
2021-03-08 13:22 ` David Hildenbrand
2021-03-08 14:11 ` Michal Hocko
2021-03-08 14:13 ` David Hildenbrand
2021-03-08 15:42 ` Michal Hocko
2021-03-08 15:58 ` Minchan Kim
2021-03-08 16:21 ` Michal Hocko
2021-03-08 17:01 ` Minchan Kim
2021-03-08 20:27 ` Minchan Kim
2021-02-18 16:10 ` Minchan Kim
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