linux-kernel - Re: ext4 deep stack with mark_page

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Message-Id: <1300206353-sup-9759@think>
Date:	Tue, 15 Mar 2011 12:26:43 -0400
From:	Chris Mason <chris.mason@...cle.com>
To:	dave <dave@...os.cz>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>, adilger <adilger@...ger.ca>
Subject: Re: ext4 deep stack with mark_page_dirty reclaim

Excerpts from David Sterba's message of 2011-03-15 11:22:22 -0400:
> On Mon, Mar 14, 2011 at 07:25:10PM -0700, Andreas Dilger wrote:
> > Is there a script which you used to generate this stack trace to
> > function size mapping, or did you do it by hand?  I've always wanted
> > such a script, but the tricky part is that there is so much garbage on
> > the stack that any automated stack parsing is almost useless.
> > Alternately, it would seem trivial to have the stack dumper print the
> > relative address of each symbol, and the delta from the previous
> > symbol...
> 
> > > 240 schedule+0x25a
> > > 368 io_schedule+0x35
> > >  32 get_request_wait+0xc6
> 
> from the callstack:
> 
> ffff88007a704338 schedule+0x25a
> ffff88007a7044a8 io_schedule+0x35
> ffff88007a7044c8 get_request_wait+0xc6
> 
> subtract the values and you get the ones Ted posted,
> 
> eg. for get_request_wait:
> 
> 0xffff88007a7044c8 - 0xffff88007a7044a8 = 32
> 
> There'se a script scripts/checkstack.pl which tries to determine stack
> usage from 'objdump -d' looking for the 'sub 0x123,%rsp' instruction and
> reporting the 0x123 as stack consumption. It does not give same results,
> for the get_request_wait:
> 
> ffffffff81216205:       48 83 ec 68             sub    $0x68,%rsp
> 
> reported as 104.

Also, the ftrace stack usage tracer gives more verbose output that
includes the size of each function.

-chris
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