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

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Message-ID: <xa1td1ga74v7.fsf@mina86.com>
Date:   Thu, 29 Dec 2016 23:22:20 +0100
From:   Michal Nazarewicz <mina86@...a86.com>
To:     Eric Anholt <eric@...olt.net>, 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.

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!

> we shouldn't be clogging dmesg with it at all.  So, I'd rather we go
> with this patch, that is unless the KERN_DEBUG in your ratelimit patch
> would keep it out of journald as well (un-ratelimited, journald was
> eating 10% of a CPU processing the message, and I'd rather it not be
> getting logged at all).

-- 
Best regards
ミハウ “𝓶𝓲𝓷𝓪86” ナザレヴイツ
«If at first you don’t succeed, give up skydiving»