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Date: Sat, 17 Apr 2010 12:37:52 +1000
From: Dave Chinner <david@fromorbit.com>
To: Mel Gorman <mel@csn.ul.ie>
Cc: Andi Kleen <andi@firstfloor.org>,
       KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
       Chris Mason <chris.mason@oracle.com>, linux-kernel@vger.kernel.org,
       linux-mm@kvack.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 1/4] vmscan: simplify shrink_inactive_list()
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On Fri, Apr 16, 2010 at 03:57:07PM +0100, Mel Gorman wrote:
> On Fri, Apr 16, 2010 at 09:40:13AM +1000, Dave Chinner wrote:
> > On Thu, Apr 15, 2010 at 06:54:16PM +0200, Andi Kleen wrote:
> > > > It's a buying-time venture, I'll agree but as both approaches are only
> > > > about reducing stack stack they wouldn't be long-term solutions by your
> > > > criteria. What do you suggest?
> > > 
> > > (from easy to more complicated):
> > > 
> > > - Disable direct reclaim with 4K stacks
> > 
> > Just to re-iterate: we're blowing the stack with direct reclaim on
> > x86_64  w/ 8k stacks. 
> 
> Yep, that is not being disputed. By the way, what did you use to
> generate your report? Was it CONFIG_DEBUG_STACK_USAGE or something else?
> I used a modified bloat-o-meter to gather my data but it'd be nice to
> be sure I'm seeing the same things as you (minus XFS unless I
> specifically set it up).

I'm using the tracing subsystem to get them. Doesn't everyone use
that now? ;)

$ grep STACK .config
CONFIG_STACKTRACE_SUPPORT=y
CONFIG_HAVE_REGS_AND_STACK_ACCESS_API=y
# CONFIG_CC_STACKPROTECTOR is not set
CONFIG_STACKTRACE=y
CONFIG_USER_STACKTRACE_SUPPORT=y
CONFIG_STACK_TRACER=y
# CONFIG_DEBUG_STACKOVERFLOW is not set
# CONFIG_DEBUG_STACK_USAGE is not set

Then:

# echo 1 > /proc/sys/kernel/stack_tracer_enabled

<run workloads>

Monitor the worst recorded stack usage as it changes via:

# cat /sys/kernel/debug/tracing/stack_trace
        Depth    Size   Location    (44 entries)
        -----    ----   --------
  0)     5584     288   get_page_from_freelist+0x5c0/0x830
  1)     5296     272   __alloc_pages_nodemask+0x102/0x730
  2)     5024      48   kmem_getpages+0x62/0x160
  3)     4976      96   cache_grow+0x308/0x330
  4)     4880      96   cache_alloc_refill+0x27f/0x2c0
  5)     4784      96   __kmalloc+0x241/0x250
  6)     4688     112   vring_add_buf+0x233/0x420
......


Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com
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