linux-ext4 - Re: [PATCH -V2 4/5] ext4: Use both hi and lo bits of the group desc values.

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Message-ID: <20081124012113.GA2163@mit.edu>
Date:	Sun, 23 Nov 2008 20:21:13 -0500
From:	Theodore Tso <tytso@....EDU>
To:	Andreas Dilger <adilger@....com>
Cc:	Eric Sandeen <sandeen@...hat.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Coly Li <coyli@...e.de>, cmm@...ibm.com,
	linux-ext4@...r.kernel.org
Subject: Re: [PATCH -V2 4/5] ext4: Use both hi and lo bits of the group
	desc values.

On Sat, Nov 22, 2008 at 10:09:39PM -0600, Andreas Dilger wrote:
> On Nov 21, 2008  11:53 -0600, Eric Sandeen wrote:
> > Ok, and for the rest?  (free_blocks, free_inodes) - I guess these are
> > only needed for > 2^32 block filesystems?
> 
> Actually, since this is a per-group number, I'm not sure why this is
> needed at all.  I don't object to keeping the helper functions though.

For most systems, it wn't be needed at all.  However, for filesystems
with block sizes >= 8k, we run into a limit where the maximum number
of blocks and inodes we can support per block group is 65528 (we can't
support 65536 since that would cause bg_free_blocks_count and/or
bg_free_blocks_count, which are both __u16 types, to overflow).  So on
systems with a page size > 4k, or if Christoph's patch to support fs
block sizes > page size ever makes it into mainline, this support
could be useful.

						- Ted
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