linux-kernel - Re: ext4 deep stack with mark_page

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Message-ID: <20110315152222.GW17108@twin.jikos.cz>
Date:	Tue, 15 Mar 2011 16:22:22 +0100
From:	David Sterba <dave@...os.cz>
To:	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Cc:	adilger@...ger.ca
Subject: Re: ext4 deep stack with mark_page_dirty reclaim

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.


dave
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