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Date: Wed, 7 Nov 2001 15:02:29 -0500 (EST)
From: Alexander Viro <viro@math.psu.edu>
To: Andreas Dilger <adilger@turbolabs.com>
cc: Stephen Tweedie <sct@redhat.com>, ext2-devel@lists.sourceforge.net,
        m@mo.optusnet.com.au, Andrew Morton <akpm@zip.com.au>,
        "Albert D. Cahalan" <acahalan@cs.uml.edu>,
        Mike Fedyk <mfedyk@matchmail.com>, lkml <linux-kernel@vger.kernel.org>
Subject: Re: [Ext2-devel] ext2/ialloc.c cleanup
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On Wed, 7 Nov 2001, Andreas Dilger wrote:

> Minor nits, from my changes to this same function:
> 1) please replace use of "i" for best block group in find_cg_*, to
>    something better like "group", just for clarity.

Consider that done.

> 2) in find_cg_*, when you fail the quadratic search, the linear search
>    should skip groups that were previously checked in the quadratic search,
>    with slight changes to both loops:

I'm not actually sure that it's a good thing.  The different between the
sequences we do is that I do
	n n+1 n+3 n+7 ... n+2 (linear)
and you do
	n n+1 n+2 n+4 n+8 ... n+3 (linear)
which has slightly worse properties.  You avoid duplicated check on n+3,
but lose a very nice property - shifting the old sequence is guaranteed
not to have many intersections with original in the beginning (distances
between elements do not repeat).  With your sequence it's no longer true.

> 3) I know that "cylinder groups" were used in old FFS/whatever implementation,
>    but all of the ext2 code/documentation refers to these as block groups.
>    Can you stick with that for ext2 (e.g. gdp, not cg; bg_foo, not cg_foo)?

Ehh... Try to read that aloud.  Maybe it's just me, but "gdp" sounds (and
looks) bad...

> 4) sbi can be gotten by "EXT2_SB(sb)".

True, consider that done.

Right now I'm doing alternative strategy for directory allocation, as soon
as I finish that I'll put the result on usual place.