linux-kernel - Re: [PATCH] mm: warn only once if page table misaccounting is detected

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Date:   Tue, 27 Nov 2018 17:29:16 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Heiko Carstens <heiko.carstens@...ibm.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
        linux-mm@...ck.org, "Kirill A . Shutemov" <kirill@...temov.name>,
        Martin Schwidefsky <schwidefsky@...ibm.com>
Subject: Re: [PATCH] mm: warn only once if page table misaccounting is
 detected

On Tue 27-11-18 15:36:38, Heiko Carstens wrote:
> On Tue, Nov 27, 2018 at 02:19:16PM +0100, Michal Hocko wrote:
> > On Tue 27-11-18 09:36:03, Heiko Carstens wrote:
> > > Use pr_alert_once() instead of pr_alert() if page table misaccounting
> > > has been detected.
> > > 
> > > If this happens once it is very likely that there will be numerous
> > > other occurrence as well, which would flood dmesg and the console with
> > > hardly any added information. Therefore print the warning only once.
> > 
> > Have you actually experience a flood of these messages? Is one per mm
> > message really that much?
> 
> Yes, I did. Since in this case all compat processes caused the message
> to appear, I saw thousands of these messages.

This means something went colossally wrong and seeing an avalanche of
messages might be actually helpful because you can at least see the
pattern. I wonder whether the underlying issue would be obvious from a
single instance.

Maybe we want ratelimit instead?
 
> > If yes why rss counters do not exhibit the same problem?
> 
> No rss counter messages appeared. Or do you suggest that the other
> pr_alert() within check_mm() should also be changed?

Whatever we go with (and I do not have a strong opinion here) we should
be consistent I believe.

-- 
Michal Hocko
SUSE Labs