linux-ext4 - Re: [PATCH 2/6 ]Ext4: journal credits reservation fixes for extent file writepage

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Date:	Wed, 13 Aug 2008 17:26:58 -0700
From:	Mingming Cao <cmm@...ibm.com>
To:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc:	tytso <tytso@....edu>, linux-ext4@...r.kernel.org,
	Andreas Dilger <adilger@....com>
Subject: Re: [PATCH 2/6 ]Ext4: journal credits reservation fixes for extent
	file writepage


在 2008-08-13三的 14:07 +0530，Aneesh Kumar K.V写道：
> On Tue, Aug 12, 2008 at 09:27:53AM -0700, Mingming Cao wrote:
> 
> ....
> ....
> 
> > 
> >  /*
> > - * ext4_ext_calc_credits_for_insert:
> > - * This routine returns max. credits that the extent tree can consume.
> > - * It should be OK for low-performance paths like ->writepage()
> > - * To allow many writing processes to fit into a single transaction,
> > - * the caller should calculate credits under i_data_sem and
> > - * pass the actual path.
> > + * ext4_ext_calc_credits_for_single_extent:
> > + * This routine returns max. credits that needed to insert an extent
> > + * to the extent tree.
> > + * When pass the actual path, the caller should calculate credits
> > + * under i_data_sem.
> >   */
> > -int ext4_ext_calc_credits_for_insert(struct inode *inode,
> > +int ext4_ext_calc_credits_for_single_extent(struct inode *inode, int num,
> >  						struct ext4_ext_path *path)
> >  {
> > -	int depth, needed;
> > +	int depth = ext_depth(inode);
> > 
> >  	if (path) {
> >  		/* probably there is space in leaf? */
> > -		depth = ext_depth(inode);
> >  		if (le16_to_cpu(path[depth].p_hdr->eh_entries)
> >  				< le16_to_cpu(path[depth].p_hdr->eh_max))
> > -			return 1;
> > +			return 2 + EXT4_META_TRANS_BLOCKS(inode->i_sb);
> >  	}
> > 
> > -	/*
> > -	 * given 32-bit logical block (4294967296 blocks), max. tree
> > -	 * can be 4 levels in depth -- 4 * 340^4 == 53453440000.
> > -	 * Let's also add one more level for imbalance.
> > -	 */
> > -	depth = 5;
> > -
> > -	/* allocation of new data block(s) */
> > -	needed = 2;
> > +	return ext4_ext_writepage_trans_blocks(inode, num, 1);
> 
> 
> single extent insert should not look at journaling mode or not
> In the above with path specified we don't look at journaling mode
> but ext4_ext_writepage_trans_blocks will do

Are you sure about this?

 ext4_ext_calc_credits_for_single_extent is actually only called from
migration and defrag with this set of changes now. In the
data=journalling mode, since we move data around (for migration and
defrag),  I think we still need to log the data buffers. I might be
over-causous.

Mingming

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