linux-ext4 - Re: [PATCH] ext4: Fix FLEX_BG and uninit group usage.

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Date:	Thu, 15 May 2008 09:36:58 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	"Jose R. Santos" <jrs@...ibm.com>
Cc:	cmm@...ibm.com, tytso@....edu, sandeen@...hat.com,
	linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext4: Fix FLEX_BG and uninit group usage.

On Wed, May 14, 2008 at 02:08:02PM -0500, Jose R. Santos wrote:
> On Thu, 15 May 2008 00:17:12 +0530
> "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com> wrote:
> 
> > With FLEX_BG we allocate block bitmap, inode bitmap, and
> > inode table outside the group. So when initialzing the
> > uninit block group we don't need to set bits corresponding
> > to these meta-data in the bitmaps. Also return the right
> > number of free blocks when counting the available free
> > blocks in uninit group.
> > 
> > Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
> > ---
> >  fs/ext4/balloc.c |   15 ++++++++++++++-
> >  1 files changed, 14 insertions(+), 1 deletions(-)
> > 
> > diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
> > index 5c80eb5..fb63f01 100644
> > --- a/fs/ext4/balloc.c
> > +++ b/fs/ext4/balloc.c
> > @@ -109,7 +109,14 @@ unsigned ext4_init_block_bitmap(struct super_block *sb, struct buffer_head *bh,
> > 
> >  		for (bit = 0; bit < bit_max; bit++)
> >  			ext4_set_bit(bit, bh->b_data);
> > -
> > +		/*
> > +		 * With FLEX_BG uninit group we have all the
> > +		 * blocks available for use. So no need
> > +		 * to set any bits in bitmap
> > +		 */
> > +		 if (EXT4_HAS_INCOMPAT_FEATURE(sb,
> > +					 EXT4_FEATURE_INCOMPAT_FLEX_BG))
> > +			return free_blocks;
> >  		start = ext4_group_first_block_no(sb, block_group);
> > 
> >  		/* Set bits for block and inode bitmaps, and inode table */
> > @@ -126,6 +133,12 @@ unsigned ext4_init_block_bitmap(struct super_block *sb, struct buffer_head *bh,
> >  		 */
> >  		mark_bitmap_end(group_blocks, sb->s_blocksize * 8, bh->b_data);
> >  	}
> > +	/*
> > +	 * With FLEX_BG uninit group we have all the
> > +	 * blocks available for use.
> > +	 */
> > +	if (EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_FLEX_BG))
> > +		return free_blocks;
> > 
> >  	return free_blocks - sbi->s_itb_per_group - 2;
> >  }
> 
> This assumes that if the FLEX_BG feature is enable that all block
> groups have no bitmaps or inode tables (which is wrong).
> 
> Something like this (ignore the fact that doesnt handle hi bits) should be better.
> 
> 	used_blocks = sbi->s_itb_per_group + 2;
> 	if (EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_FLEX_BG)) {
> 		ext4_get_group_no_and_offset(sbi, bgd->bg_block_bitmap_lo, tmp, 0);
> 		if (tmp != block_group)
> 			used_blocks--;
> 		ext4_get_group_no_and_offset(sbi, bgd->bg_inode_bitmap_lo, tmp, 0);
> 		if (tmp != block_group)
> 			used_blocks--;
> 		ext4_get_group_no_and_offset(sbi, bgd->bg_inode_table_lo, tmp, 0);
> 		if (tmp != block_group)
> 			used_blocks -= sbi->s_itb_per_group;
> 	}
> 
>  	return free_blocks - used_blocks;
>  }

But with FLEX_BG won't we mark the group as initialized if we are
placing the bitmap or inode table in the group ?

-aneesh
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