linux-kernel - Re: [PATCH] Increase maximum size of dmesg buffer to 16MB.

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Date:	Fri, 12 Dec 2014 23:45:15 +0100
From:	"Luis R. Rodriguez" <mcgrof@...e.com>
To:	Vinson Lee <vlee@...pensource.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Michal Hocko <mhocko@...e.cz>,
	Josh Triplett <josh@...htriplett.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Fabian Frederick <fabf@...net.be>,
	Bertrand Jacquin <beber@...eeweb.net>,
	Andy Lutomirski <luto@...capital.net>,
	Pranith Kumar <bobby.prani@...il.com>,
	Peter Foley <pefoley2@...oley.com>,
	Clark Williams <clark.williams@...il.com>,
	Mel Gorman <mgorman@...e.de>, linux-kernel@...r.kernel.org,
	Nate Stahl <stahl@...tter.com>, Vinson Lee <vlee@...tter.com>
Subject: Re: [PATCH] Increase maximum size of dmesg buffer to 16MB.

On Fri, Dec 12, 2014 at 02:38:26PM -0800, Vinson Lee wrote:
> From: Nate Stahl <stahl@...tter.com>
> 
> A full task stack dump of all tasks on a machine can generate more than
> 4MB of output to dmesg. Dumping this data to the serial console causes
> the machine to hang for a number of minutes (an unacceptable impact),
> but dumping the same data to memory is feasible if the dmesg buffer is
> sized large enough to hold the output. Set to 16MB which will hopefully
> be large enough to handle a dump from any of our servers at this time.
> 
> Signed-off-by: Nate Stahl <stahl@...tter.com>
> Signed-off-by: Vinson Lee <vlee@...tter.com>

Isn't this the perpetual issue of having large number of CPUs? If so
consider use of LOG_CPU_MAX_BUF_SHIFT instead, otherwise clarifying how
this would be a different issue would be good. LOG_CPU_MAX_BUF_SHIFT
should scale nicely but you can increase it as well, is it being used?

 Luis
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