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Date:	Thu, 28 Aug 2008 22:02:10 -0700
From:	Mingming Cao <cmm@...ibm.com>
To:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc:	tytso@....edu, sandeen@...hat.com, linux-ext4@...r.kernel.org
Subject: Re: [PATCH -V3 09/11] ext4: Fix ext4 nomballoc allocator for ENOSPC


在 2008-08-29五的 09:44 +0530,Aneesh Kumar K.V写道:
> On Fri, Aug 29, 2008 at 09:14:51AM +0530, Aneesh Kumar K.V wrote:
> > On Thu, Aug 28, 2008 at 02:57:49PM -0700, Mingming Cao wrote:
> > > 
> > > From: Mingming Cao <cmm@...ibm.com>
> > > 
> > > ext4: Fix ext4 nomballoc allocator for ENOSPC
> > >     
> > > We run into ENOSPC error on nonmballoc ext4, even when there is free blocks
> > > on the filesystem.
> > > 
> > > The problem is triggered in the case the goal block group has 0 free blocks
> > > , and the rest block groups are skipped due to the check of "free_blocks 
> > > < windowsz/2".
> > 
> > The goal block group had free blocks < windowsz .
> > 
> > 
> 
> Ok how about this. The Final change is same to what you have done.
> But it make the code easier to understand. I also added a comment
> explaining the details
> 

Fine with me, I will update the patch in the ext4 patch queue with
additional comment.  But Andrew has already took ext2/3 version to mm
tree, I am not sure if it worth to resend with an patch against original
patch.

> commit 0216ee1ac13270c1ab7b7517d41775727f7da02d
> Author: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
> Date:   Fri Aug 29 09:35:15 2008 +0530
> 
>     ext4: Fix ext4 nomballoc allocator for ENOSPC
>     
>     We run into ENOSPC error on nonmballoc ext4, even when there is free blocks
>     on the filesystem.
>     
>     The patch include two changes
>     
>     a) Set reservation to NULL if we trying to allocate near group_target_block
>     from the goal group if the free block in the group is less than windowsz.
>     This should give us a better chance to allocate near group_target_block.
>     This also ensures that if we are not allocating near group_target_block
>     then we don't trun off reservation. This should enable us to allocate
>     with reservation from other groups that have large free blocks count.
>     
>     b) we don't need to check the window size if the block reservation is off.
>     
>     Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
>     Signed-off-by: Mingming Cao <cmm@...ibm.com>
> 
> diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
> index cfe01b4..399bec5 100644
> --- a/fs/ext4/balloc.c
> +++ b/fs/ext4/balloc.c
> @@ -1802,15 +1802,17 @@ ext4_fsblk_t ext4_old_new_blocks(handle_t *handle, struct inode *inode,
>  		goto io_error;
> 
>  	free_blocks = le16_to_cpu(gdp->bg_free_blocks_count);
> -	/*
> -	 * if there is not enough free blocks to make a new resevation
> -	 * turn off reservation for this allocation
> -	 */
> -	if (my_rsv && (free_blocks < windowsz)
> -		&& (rsv_is_empty(&my_rsv->rsv_window)))
> -		my_rsv = NULL;
> 
>  	if (free_blocks > 0) {
> +		/*
> +		 * try to allocate with group target block
> +		 * in the goal group. If we have low free_blocks
> +		 * count turn off reservation
> +		 */
> +		if (my_rsv && (free_blocks < windowsz)
> +			&& (rsv_is_empty(&my_rsv->rsv_window)))
> +			my_rsv = NULL;
> +
>  		bitmap_bh = ext4_read_block_bitmap(sb, group_no);
>  		if (!bitmap_bh)
>  			goto io_error;
> @@ -1843,7 +1845,7 @@ ext4_fsblk_t ext4_old_new_blocks(handle_t *handle, struct inode *inode,
>  		 * free blocks is less than half of the reservation
>  		 * window size.
>  		 */
> -		if (free_blocks <= (windowsz/2))
> +		if (my_rsv && (free_blocks <= (windowsz/2)))
>  			continue;
> 
>  		brelse(bitmap_bh);

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