linux-kernel - Re: [PATCH] mm: simplify node/zone name printing

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Message-ID: <20161219140312.GG5164@dhcp22.suse.cz>
Date:   Mon, 19 Dec 2016 15:03:12 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...e.de>,
        Johannes Weiner <hannes@...xchg.org>,
        Joonsoo Kim <js1304@...il.com>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: Re: [PATCH] mm: simplify node/zone name printing

On Mon 19-12-16 11:27:59, Petr Mladek wrote:
> On Mon 2016-12-19 09:12:10, Michal Hocko wrote:
> > On Mon 19-12-16 16:32:28, Sergey Senozhatsky wrote:
> > [...]
> > > as far as I can tell, now for_each_populated_zone() iterations are
> > > split by non-CONT printk() from show_zone_node(), which previously
> > > has been   printk(KERN_CONT "%s: ", zone->name), so pr_cont(\n)
> > > between iterations was important, but now that non-CONT printk()
> > > should do the trick. it's _a bit_ hacky, though.
> > 
> > Do you consider that more hacky than the original? At least for me,
> > starting with KERN_CONT and relying on an explicit \n sounds more error
> > prone than leaving the last pr_cont without \n and relying on the
> > implicit flushing.
> 
> The missing '\n' will cause the string will not be flushed
> until another printk happens. It is not a problem here because
> other printk follows. But it might take a while in general.
> 
> There was a commit[1] that flushed the cont lines when the log
> buffer was read via /dev/kmsg or syslog. Also there was a patch[2]
> that flushed cont lines using a timer. But the commit caused problems
> and was reverted[3]. Also the patch needs more testing. So, it might
> take a while until flushing partial cont lines is "guaranteed".

OK, fair enough. If the flushing partial cont lines is not guaranteed
then this cleanup makes less sense. I was under impression this has been
solved but as per your list of commits we are not there yet.

So let's just drop this patch and I will try to remember to double check
later.

Thanks!

-- 
Michal Hocko
SUSE Labs