Re: [PATCH 1/6 ]Ext4 credits caclulation cleanup and fix that for nonextent writepage

[Mingming Cao <cmm@us.ibm.com>]

在 2008-08-13三的 14:01 +0530，Aneesh Kumar K.V写道：
> On Tue, Aug 12, 2008 at 09:25:54AM -0700, Mingming Cao wrote:
> 
> ....
> 
> 
> > - * and dindirect block, and the "5" above becomes "3".
> > + * Also account for superblock, inode, quota and xattr blocks
> > + */
> > +int ext4_meta_trans_blocks(struct inode* inode, int nrblocks, int idxblocks)
> > +{
> > +	int groups, gdpblocks;
> > +	int ret = 0;
> > +
> > +	groups = nrblocks + idxblocks;
> > +	gdpblocks = groups;
> > +	if (groups > EXT4_SB(inode->i_sb)->s_groups_count)
> > +		groups = EXT4_SB(inode->i_sb)->s_groups_count;
> > +	if (groups > EXT4_SB(inode->i_sb)->s_gdb_count)
> > +		gdpblocks = EXT4_SB(inode->i_sb)->s_gdb_count;
> > +
> > +	/* bitmaps and block group descriptor blocks */
> > +	ret += groups + gdpblocks;
> 
> 
> 	ret = groups + gdpblocks;
> 
> > +
> > +	ret += idxblocks;
> > +
> > +	/* journalled mode, include buffer to modify data blocks */
> > +	if (ext4_should_journal_data(inode))
> > +		ret += nrblocks;
> > +
> > +	/* Blocks for super block, inode, quota and xattr blocks */
> > +	ret += EXT4_META_TRANS_BLOCKS(inode->i_sb);
> > +
> > +	return ret;
> > +}
> > +
> > +static int ext4_indirect_trans_blocks(struct inode *inode, int nrblocks,
> > +				      int chunk)
> > +{
> 
> .....
> .....
> 
> > 
> > +/*
> > + * Define the number of metadata blocks we need to account to modify data.
> > + *
> > + * This include super block, inode block, quota blocks and xattr blocks
> > + */
> > +#define EXT4_META_TRANS_BLOCKS(sb)	(EXT4_XATTR_TRANS_BLOCKS + \
> > +					2*EXT4_QUOTA_TRANS_BLOCKS(sb))
> > +
> 
> Do EXT4_XATTR_TRANS_BLOCKS blocks really account for super block
> and inode block ?
Yes, here is the define

/* Extended attribute operations touch at most two data buffers,
 * two bitmap buffers, and two group summaries, in addition to the inode
 * and the superblock, which are already accounted for. */

#define EXT4_XATTR_TRANS_BLOCKS         6U


>  Looking at EXT4_DATA_TRANS_BLOCKS which also use
> EXT4_XATTR_TRANS_BLOCKS I think it doesn't.

It's pretty clear from the comment.  

/* Define the minimum size for a transaction which modifies data.  This
 * needs to take into account the fact that we may end up modifying two
 * quota files too (one for the group, one for the user quota).  The
 * superblock only gets updated once, of course, so don't bother
 * counting that again for the quota updates. */

#define EXT4_DATA_TRANS_BLOCKS(sb)
(EXT4_SINGLEDATA_TRANS_BLOCKS(sb) + \
                                         EXT4_XATTR_TRANS_BLOCKS - 2 + \
                                         2*EXT4_QUOTA_TRANS_BLOCKS(sb))

It does have  "-2" in  EXT4_DATA_TRANS_BLOCKS to remove double accounted
super and inode block


Mingming

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