linux-ext4 - Re: [PATCH 14/38] fallthru: ext2 fallthru support

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Message-Id: <E1Oldyc-00062G-Ab@pomaz-ex.szeredi.hu>
Date:	Wed, 18 Aug 2010 10:26:26 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	Valerie Aurora <vaurora@...hat.com>
CC:	miklos@...redi.hu, jack@...e.cz, agruen@...e.de,
	viro@...iv.linux.org.uk, jblunck@...e.de, hch@...radead.org,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	tytso@....edu, linux-ext4@...r.kernel.org
Subject: Re: [PATCH 14/38] fallthru: ext2 fallthru support

On Tue, 17 Aug 2010, Valerie Aurora wrote:
> >  - hard links to make sure a separate inode is not necessary for each
> >    whiteout/fallthrough entry
> 
> The problem with hard links is that you run into hard link limits.  I
> don't think we can do hard links for whiteouts and fallthrus.  Each
> whiteout or fallthru will cost an inode if we implement them as
> extended attributes.  This cost has to be balanced against the cost of
> implementing them as dentries, which is mainly code complexity in
> individual file systems.

get_unlinked_inode() is a great idea.  But I feel that individual
inodes for each fallthrough is excessive.  It'll make the first
readdir() really really expensive and wastes a lot of disk and memory
for no good reason.

Not sure how to fix the hard link limits problem though...

Thanks,
Miklos
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