linux-kernel - Re: [RFC][PATCH] ChunkFS: fs fission for faster fsck

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Message-ID: <20070426160504.GA7970@c2.user-mode-linux.org>
Date:	Thu, 26 Apr 2007 12:05:04 -0400
From:	Jeff Dike <jdike@...toit.com>
To:	Amit Gud <gud@....edu>
Cc:	Valerie Henson <val_henson@...ux.intel.com>,
	Nikita Danilov <nikita@...sterfs.com>,
	David Lang <david.lang@...italinsight.com>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	riel@...riel.com, zab@...bo.net, arjan@...radead.org,
	suparna@...ibm.com, brandon@...p.org, karunasagark@...il.com
Subject: Re: [RFC][PATCH] ChunkFS: fs fission for faster fsck

On Thu, Apr 26, 2007 at 10:53:16AM -0500, Amit Gud wrote:
> Jeff Dike wrote:
> >How about this case:
> >
> >	Growing file starts in chunk A.
> >	Overflows into chunk B.
> >	Delete file in chunk A.
> >	Growing file overflows chunk B and spots new free space in
> >chunk A (and nothing anywhere else)
> >	Overflows into chunk A
> >	Delete file in chunk B.
> >	Overflow into chunk B again.
> >
> >Maybe this is not realistic, but in the absence of a mechanism to pull
> >data back from an overflow chunk, it seems at least a theoretical
> >possibility that there could be > 1 continuation inodes per file per
> >chunk.
> >
> 
> Preventive measures are taken to limit only one continuation inode per 
> file per chunk. This can be done easily in the chunk allocation 
> algorithm for disk space. Although I'm not quite sure what you mean by 
> "Delete file in chunk A". If you are referring to same file thats 
> growing, then deletion is not possible, because individual parts of any 
> file in any chunk cannot be deleted.

No, I'm referring to a different file.  The scenario is that you have
a growing file in a nearly full disk with files being deleted (and
thus space being freed) such that allocations for the growing file
bounce back and forth between chunks.

				Jeff

-- 
Work email - jdike at linux dot intel dot com
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