linux-ext4 - Re: [RFC]Ext4: journal credits reservation fixes for DIO, fallocate and delalloc writepages

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Date:	Wed, 23 Jul 2008 22:07:03 -0400
From:	Andreas Dilger <adilger@....com>
To:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc:	Mingming Cao <cmm@...ibm.com>, tytso <tytso@....edu>,
	Shehjar Tikoo <shehjart@....unsw.edu.au>,
	linux-ext4@...r.kernel.org
Subject: Re: [RFC]Ext4: journal credits reservation fixes for DIO,
	fallocate and delalloc writepages

On Jul 23, 2008  13:12 +0530, Aneesh Kumar wrote:
> On Tue, Jul 22, 2008 at 05:51:51PM -0700, Mingming Cao wrote:
> > @@ -1930,9 +1931,6 @@ int ext4_ext_calc_credits_for_insert(str
> >  	 */
> >  	needed += (depth * 2) + (depth * 2);
> > 
> > -	/* any allocation modifies superblock */
> > -	needed += 1;
> 
> Why are we dropping the super block modification credit ? An insert of
> an extent can result in super block modification also. If the goal is to
> use ext4_writepages_trans_blocks everywhere then this change is correct.
> But i see  many place not using ext4_writepages_trans_blocks.

We used to need to update the superblock on every allocation operation
(block or inode).  That was removed a long time ago, and we rarely
update the superblock these days.

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.

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