linux-ext4 - Re: [PATCH 01/02] ext2: reserve INCOMPAT

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Message-ID: <20111207003932.GI7137@tux1.beaverton.ibm.com>
Date:	Tue, 6 Dec 2011 16:39:32 -0800
From:	"Darrick J. Wong" <djwong@...ibm.com>
To:	Andreas Dilger <adilger@...mcloud.com>
Cc:	"Theodore Ts'o" <tytso@....edu>,
	ext4 development <linux-ext4@...r.kernel.org>,
	Liang Zhen <liang@...mcloud.com>, Tao Ma <tm@....ma>
Subject: Re: [PATCH 01/02] ext2: reserve INCOMPAT_INLINEDATA feature flag

On Tue, Dec 06, 2011 at 05:13:51PM -0700, Andreas Dilger wrote:
> Reserve the EXT4_FEATURE_INCOMPAT_INLINEDATA feature flag for use
> with storing small file data in the i_blocks field (up to 60 bytes)
> and/or the large xattr space (after i_extra_isize, up to the large
> inode size).  On typical filesystems this can save 1-3% of the space,
> and more importantly it also avoids seeking to read the data block.
> 
> This will become increasingly important with bigalloc filesystems,
> since they consume a full cluster of blocks for each file, including
> small directories that could easily fit into the inode itself.
> 
> Signed-off-by: Andreas Dilger <adilger@...mcloud.com>
> Originally-by: Tao Ma <tm@....ma>
> ---
>  lib/ext2fs/ext2_fs.h |    1 +
>  1 files changed, 1 insertions(+), 0 deletions(-)
> 
> diff --git a/lib/ext2fs/ext2_fs.h b/lib/ext2fs/ext2_fs.h
> index 0f8cde8..6cf47f9 100644
> --- a/lib/ext2fs/ext2_fs.h
> +++ b/lib/ext2fs/ext2_fs.h
> @@ -719,6 +719,7 @@ struct ext2_super_block {
>  #define EXT4_FEATURE_INCOMPAT_FLEX_BG		0x0200
>  #define EXT4_FEATURE_INCOMPAT_EA_INODE		0x0400
>  #define EXT4_FEATURE_INCOMPAT_DIRDATA		0x1000
> +#define EXT4_FEATURE_INCOMPAT_INLINEDATA	0x2000 /* data in inode */

I was using 0x2000 for EXT4_FEATURE_INCOMPAT_BG_USE_META_CSUM, to change the
block group checksum to use crc32c.

--D
> 
>  #define EXT2_FEATURE_COMPAT_SUPP	0
>  #define EXT2_FEATURE_INCOMPAT_SUPP    (EXT2_FEATURE_INCOMPAT_FILETYPE| \
> -- 
> 1.7.2
> 
> 
> 
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