linux-ext4 - Re: Question on block group allocation

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Message-ID: <6601abe90904291529o5aaab638i73bd34c1a6d54c74@mail.gmail.com>
Date:	Wed, 29 Apr 2009 15:29:55 -0700
From:	Curt Wohlgemuth <curtw@...gle.com>
To:	Theodore Tso <tytso@....edu>
Cc:	Andreas Dilger <adilger@....com>,
	ext4 development <linux-ext4@...r.kernel.org>
Subject: Re: Question on block group allocation

Hi Ted:

On Wed, Apr 29, 2009 at 2:50 PM, Theodore Tso <tytso@....edu> wrote:
> Oh --- one more question.  You did these tests on your 2.6.26-based
> kernel with ext4 backports, right?  Not 2.6.30 mainline kernel?  Did
> you backport the changes to the block and inode allocators?  i.e.,
> this patch (plus a 1 or 2 subsequent bug fixes)?
>
>
> commit a4912123b688e057084e6557cef8924f7ae5bbde
> Author: Theodore Ts'o <tytso@....edu>
> Date:   Thu Mar 12 12:18:34 2009 -0400
>
>    ext4: New inode/block allocation algorithms for flex_bg filesystems

Yes, we have this patch.  I'm not sure if we have the "1 or 2" bug
fixes you refer to above; do you have commits for these?

I'm regen'ing the e2fsck and debugfs output for the 3 "dd" sequence
above, for our stock kernel and for this + Andreas' patch.

Thanks,
Curt

>
>    The find_group_flex() inode allocator is now only used if the
>    filesystem is mounted using the "oldalloc" mount option.  It is
>    replaced with the original Orlov allocator that has been updated for
>    flex_bg filesystems (it should behave the same way if flex_bg is
>    disabled).  The inode allocator now functions by taking into account
>    each flex_bg group, instead of each block group, when deciding whether
>    or not it's time to allocate a new directory into a fresh flex_bg.
>
>    The block allocator has also been changed so that the first block
>    group in each flex_bg is preferred for use for storing directory
>    blocks.  This keeps directory blocks close together, which is good for
>    speeding up e2fsck since large directories are more likely to look
>    like this:
>
>    debugfs:  stat /home/tytso/Maildir/cur
>    Inode: 1844562   Type: directory    Mode:  0700   Flags: 0x81000
>    Generation: 1132745781    Version: 0x00000000:0000ad71
>    User: 15806   Group: 15806   Size: 1060864
>    File ACL: 0    Directory ACL: 0
>    Links: 2   Blockcount: 2072
>    Fragment:  Address: 0    Number: 0    Size: 0
>     ctime: 0x499c0ff4:164961f4 -- Wed Feb 18 08:41:08 2009
>     atime: 0x499c0ff4:00000000 -- Wed Feb 18 08:41:08 2009
>     mtime: 0x49957f51:00000000 -- Fri Feb 13 09:10:25 2009
>    crtime: 0x499c0f57:00d51440 -- Wed Feb 18 08:38:31 2009
>    Size of extra inode fields: 28
>    BLOCKS:
>    (0):7348651, (1-258):7348654-7348911
>    TOTAL: 259
>
>    Signed-off-by: "Theodore Ts'o" <tytso@....edu>
>
>                                                - Ted
>
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