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Re: BUG() in end_page_writeback(), stack overflows and system speed decr

To: Juergen Urban <JuergenUrban@xxxxxx>
Subject: Re: BUG() in end_page_writeback(), stack overflows and system speed decrease with XFS over USB
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Sun, 22 Nov 2009 09:04:44 +1100
Cc: xfs@xxxxxxxxxxx
In-reply-to: <200911211833.20691.JuergenUrban@xxxxxx>
References: <200911190957.45957.JuergenUrban@xxxxxx> <200911210200.13438.JuergenUrban@xxxxxx> <200911211151.23764@xxxxxx> <200911211833.20691.JuergenUrban@xxxxxx>
User-agent: Mutt/1.5.18 (2008-05-17)
On Sat, Nov 21, 2009 at 06:33:20PM +0100, Juergen Urban wrote:
> Can someone explain the purpose of the BUG() in end_page_writeback()? Can I 
> remove the line?

A page that is under writeback is supposed to have the PG_writeback
flag set. Hence when writeback is completed (i.e the page is now
clean) we need to clear the PG_writeback bit. The BUG is triggered
if we are ending writeback on a page that does not have PG_writeback
set. IOWs, something is seriously wrong, and could be a memory error
or memory corruption.

> Will XFS also work if I disable all address operations?

No.

> What is the purpose of the address operations?

Reading Documentation/filesystems/vfs.txt might answer your
questions....

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx

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