linux-kernel - Re: [PATCH] mm: Drop "PFNs busy" printk in an expected path.

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Message-ID: <8737h65nr5.fsf@eliezer.anholt.net>
Date:   Thu, 29 Dec 2016 15:17:18 -0800
From:   Eric Anholt <eric@...olt.net>
To:     Michal Nazarewicz <mina86@...a86.com>,
        Michal Hocko <mhocko@...nel.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-stable <stable@...r.kernel.org>,
        "Robin H. Johnson" <robbat2@...is-terrarum.net>,
        Vlastimil Babka <vbabka@...e.cz>,
        Marek Szyprowski <m.szyprowski@...sung.com>
Subject: Re: [PATCH] mm: Drop "PFNs busy" printk in an expected path.

Michal Nazarewicz <mina86@...a86.com> writes:

> On Thu, Dec 29 2016, Eric Anholt wrote:
>> Michal Hocko <mhocko@...nel.org> writes:
>>
>>> This has been already brought up
>>> http://lkml.kernel.org/r/20161130092239.GD18437@dhcp22.suse.cz and there
>>> was a proposed patch for that which ratelimited the output
>>> http://lkml.kernel.org/r/20161130132848.GG18432@dhcp22.suse.cz resp.
>>> http://lkml.kernel.org/r/robbat2-20161130T195244-998539995Z@orbis-terrarum.net
>>>
>>> then the email thread just died out because the issue turned out to be a
>>> configuration issue. Michal indicated that the message might be useful
>>> so dropping it completely seems like a bad idea. I do agree that
>>> something has to be done about that though. Can we reconsider the
>>> ratelimit thing?
>>
>> I agree that the rate of the message has gone up during 4.9 -- it used
>> to be a few per second.
>
> Sounds like a regression which should be fixed.
>
> This is why I don’t think removing the message is a good idea.  If you
> suddenly see a lot of those messages, something changed for the worse.
> If you remove this message, you will never know.
>
>> However, if this is an expected path during normal operation,
>
> This depends on your definition of ‘expected’ and ‘normal’.
>
> In general, I would argue that the fact those ever happen is a bug
> somewhere in the kernel – if memory is allocated as movable, it should
> be movable damn it!

I was taking "expected" from dae803e165a11bc88ca8dbc07a11077caf97bbcb --
if this is a actually a bug, how do we go about debugging it?

I've had Raspbian carrying a patch downstream to remove the error
message for 2 years now, and I either need to get this fixed or get this
patch merged to Fedora and Debian as well, now that they're shipping
some support for Raspberry Pi.

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