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Date:	Mon, 2 Jun 2008 12:25:14 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	Mingming Cao <cmm@...ibm.com>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: [RFC][PATCH 3/6] delalloc ENOSPC: reserve blocks

On Mon, Jun 02, 2008 at 12:14:33PM +0530, Aneesh Kumar K.V wrote:
> On Sun, Jun 01, 2008 at 04:35:55PM -0700, Mingming Cao wrote:
> > ext4: delalloc ENOSPC handling core
> > 
> > From: Mingming cao <cmm@...ibm.com>
> > 
> > Core part of delaloc ENOSPC (block reservation.) 
> > data/meta blocks are reserved on write_begin(), and per-inode reserved counters
> > are updated  after block allocation.
> > 
> > Signed-off-by: Mingming cao <cmm@...ibm.com>
> > 
> > ---
> >  fs/ext4/inode.c |   69 +++++++++++++++++++++++++++++++++++++++++++++++++++++---
> >  1 file changed, 66 insertions(+), 3 deletions(-)
> > 
> > Index: linux-2.6.26-rc4/fs/ext4/inode.c
> > ===================================================================
> > --- linux-2.6.26-rc4.orig/fs/ext4/inode.c	2008-06-01 14:26:13.000000000 -0700
> > +++ linux-2.6.26-rc4/fs/ext4/inode.c	2008-06-01 15:04:06.000000000 -0700
> > @@ -38,6 +38,7 @@
> >  #include "ext4_jbd2.h"
> >  #include "xattr.h"
> >  #include "acl.h"
> > +#include "ext4_extents.h"
> > 
> >  static void ext4_invalidatepage(struct page *page, unsigned long offset);
> > 
> > @@ -1410,6 +1411,61 @@ static int ext4_journalled_write_end(str
> >  	return ret ? ret : copied;
> >  }
> > 
> > +static int ext4_da_reserve_space(struct inode *inode, int nrblocks)
> > +{
> > +       struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
> > +       unsigned long md_needed, mdblocks, total = 0;
> > +
> > +       /*
> > +        * calculate the amount of metadata blocks to reserve
> 
> 	 recalculate the amount of metadata blocks to reserve.
> 
> 
> 
> 
> > +	* in order to allocate nrblocks
> > +	* worse case is one extent per block
> > +	*/
> > +	total = EXT4_I(inode)->i_reserved_data_blocks + nrblocks;
> > +	mdblocks = ext4_ext_calc_metadata_amount(inode, total);
> > +	BUG_ON(mdblocks < EXT4_I(inode)->i_reserved_meta_blocks);
> > +
> > +	md_needed = mdblocks - EXT4_I(inode)->i_reserved_meta_blocks;
> > +	total = md_needed + nrblocks;
> > +
> > +	if (ext4_has_free_blocks(sbi, total) < total)
> > +		return -ENOSPC;
> > +
> > +	/* reduce fs free blocks counter */
> > +	percpu_counter_sub(&sbi->s_freeblocks_counter, total);
> > +
> > +	EXT4_I(inode)->i_reserved_data_blocks += nrblocks;
> > +	EXT4_I(inode)->i_reserved_meta_blocks += md_needed;
> 
> Better written as
> 	EXT4_I(inode)->i_reserved_meta_blocks += mdblocks;
> 
> 
	EXT4_I(inode)->i_reserved_meta_blocks = mdblocks;

-aneesh
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