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[PATCH] Increase maximum size of dmesg buffer to 16MB.
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Vinson Lee
Dec 12, 2014, 5:38:43 PM12/12/14
to Andrew Morton, Paul E. McKenney, Michal Hocko, Josh Triplett, Johannes Weiner, Geert Uytterhoeven, Fabian Frederick, Bertrand Jacquin, Luis R. Rodriguez, Andy Lutomirski, Pranith Kumar, Peter Foley, Clark Williams, Mel Gorman, linux-...@vger.kernel.org, Nate Stahl, Vinson Lee
From: Nate Stahl <st...@twitter.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 <st...@twitter.com>
Signed-off-by: Vinson Lee <vl...@twitter.com>
---
init/Kconfig | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/init/Kconfig b/init/Kconfig
index 903505e..266a3e8 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -812,7 +812,7 @@ config IKCONFIG_PROC
config LOG_BUF_SHIFT
int "Kernel log buffer size (16 => 64KB, 17 => 128KB)"
- range 12 21
+ range 12 24
default 17
depends on PRINTK
help
--
1.9.1
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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 <st...@twitter.com>
Signed-off-by: Vinson Lee <vl...@twitter.com>
---
init/Kconfig | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/init/Kconfig b/init/Kconfig
index 903505e..266a3e8 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -812,7 +812,7 @@ config IKCONFIG_PROC
config LOG_BUF_SHIFT
int "Kernel log buffer size (16 => 64KB, 17 => 128KB)"
- range 12 21
+ range 12 24
default 17
depends on PRINTK
help
--
1.9.1
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majo...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Luis R. Rodriguez
Dec 12, 2014, 5:45:26 PM12/12/14
to Vinson Lee, Andrew Morton, Paul E. McKenney, Michal Hocko, Josh Triplett, Johannes Weiner, Geert Uytterhoeven, Fabian Frederick, Bertrand Jacquin, Andy Lutomirski, Pranith Kumar, Peter Foley, Clark Williams, Mel Gorman, linux-...@vger.kernel.org, Nate Stahl, Vinson Lee
On Fri, Dec 12, 2014 at 02:38:26PM -0800, Vinson Lee wrote:
> From: Nate Stahl <st...@twitter.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 <st...@twitter.com>
> Signed-off-by: Vinson Lee <vl...@twitter.com>
Isn't this the perpetual issue of having large number of CPUs? If so
> From: Nate Stahl <st...@twitter.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 <st...@twitter.com>
> Signed-off-by: Vinson Lee <vl...@twitter.com>
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
Vinson Lee
Dec 12, 2014, 6:07:37 PM12/12/14
to Luis R. Rodriguez, Andrew Morton, Paul E. McKenney, Michal Hocko, Josh Triplett, Johannes Weiner, Geert Uytterhoeven, Fabian Frederick, Bertrand Jacquin, Andy Lutomirski, Pranith Kumar, Peter Foley, Clark Williams, Mel Gorman, LKML, Nate Stahl, Vinson Lee
On Fri, Dec 12, 2014 at 2:45 PM, Luis R. Rodriguez <mcg...@suse.com> wrote:
> On Fri, Dec 12, 2014 at 02:38:26PM -0800, Vinson Lee wrote:
>> From: Nate Stahl <st...@twitter.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 <st...@twitter.com>
>> Signed-off-by: Vinson Lee <vl...@twitter.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
No, it is not being used.
> On Fri, Dec 12, 2014 at 02:38:26PM -0800, Vinson Lee wrote:
>> From: Nate Stahl <st...@twitter.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 <st...@twitter.com>
>> Signed-off-by: Vinson Lee <vl...@twitter.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
LOG_CPU_MAX_BUF_SHIFT is a 3.17+ config and we do not have any of the
above mentioned production machines running 3.17 or later. This patch
did help us with debugging when running on older stable kernels
though.
Thanks for the quick reply.
Luis R. Rodriguez
Dec 12, 2014, 6:29:15 PM12/12/14
to Vinson Lee, Andrew Morton, Paul E. McKenney, Michal Hocko, Josh Triplett, Johannes Weiner, Geert Uytterhoeven, Fabian Frederick, Bertrand Jacquin, Andy Lutomirski, Pranith Kumar, Peter Foley, Clark Williams, Mel Gorman, LKML, Nate Stahl, Vinson Lee
On Fri, Dec 12, 2014 at 03:07:23PM -0800, Vinson Lee wrote:
> On Fri, Dec 12, 2014 at 2:45 PM, Luis R. Rodriguez <mcg...@suse.com> wrote:
> > On Fri, Dec 12, 2014 at 02:38:26PM -0800, Vinson Lee wrote:
> >> From: Nate Stahl <st...@twitter.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 <st...@twitter.com>
> >> Signed-off-by: Vinson Lee <vl...@twitter.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
>
>
> No, it is not being used.
>
> LOG_CPU_MAX_BUF_SHIFT is a 3.17+ config and we do not have any of the
> above mentioned production machines running 3.17 or later.
Then consider backporting it.
> On Fri, Dec 12, 2014 at 2:45 PM, Luis R. Rodriguez <mcg...@suse.com> wrote:
> > On Fri, Dec 12, 2014 at 02:38:26PM -0800, Vinson Lee wrote:
> >> From: Nate Stahl <st...@twitter.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 <st...@twitter.com>
> >> Signed-off-by: Vinson Lee <vl...@twitter.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
>
>
> No, it is not being used.
>
> LOG_CPU_MAX_BUF_SHIFT is a 3.17+ config and we do not have any of the
> above mentioned production machines running 3.17 or later.
> This patch did help us with debugging when running on older stable kernels
> though.
Luis
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