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

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Date:	Thu, 26 Apr 2007 11:44:51 -0500
From:	Amit Gud <gud@....edu>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
CC:	Jeff Dike <jdike@...toit.com>,
	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

Alan Cox wrote:
>> 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 
> 
> How are you handling the allocation in this situation, are you assuming
> that a chunk is "out of bounds" because part of a file already lives on
> it or simply keeping a single inode per chunk which has multiple sparse
> pieces of the file on it ?
> 
> ie if I write 0-8MB to chunk A and then 8-16 to chunk B can I write
> 16-24MB to chunk A producing a single inode of 0-8 16-24, or does it have
> to find another chunk to use ?

Hello Alan,

You re-use the same inode with multiple sparse pieces.

This way you avoid hopping around continuation inodes and coming back to 
same chunk with which you started but this time on a different 
continuation inode. This may not be I/O intensive for successive 
traversals if the continuation inodes are pinned in the memory, but it 
certainly is a waste of resource - inodes. Not allowing this would make 
worst case of every file having a continuation inode in every chunk, 
even worse; may be like only single file exist in the file system and 
rest all inodes in all chunks (including file's own chunk) are 
continuation inodes.


AG
-- 
May the source be with you.
http://www.cis.ksu.edu/~gud

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