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Date:	Tue, 19 Aug 2008 11:07:30 -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] ext4: limit nrblocks properly with non extent format


在 2008-08-19二的 12:18 +0530,Aneesh Kumar K.V写道:
> We need to make sure adding new buffer_head to the
> contiguous block extent doesn't result in nrblocks
> greater than EXT4_MAX_TRANS_DATA. We only have
> enought credit to insert EXT4_MAX_TRANS_DATA blocks.
> 
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>

Reviewed-by: Mingming Cao <cmm@...ibm.com>
> ---
>  fs/ext4/inode.c |   38 +++++++++++++++++++++++++-------------
>  1 files changed, 25 insertions(+), 13 deletions(-)
> 
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index dcd1337..a10f8e5 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -1909,27 +1909,39 @@ static int  mpage_da_map_blocks(struct mpage_da_data *mpd)
>  static void mpage_add_bh_to_extent(struct mpage_da_data *mpd,
>  				   sector_t logical, struct buffer_head *bh)
>  {
> -	struct buffer_head *lbh = &mpd->lbh;
>  	sector_t next;
> +	size_t b_size = bh->b_size;
> +	struct buffer_head *lbh = &mpd->lbh;
>  	int nrblocks = lbh->b_size >> mpd->inode->i_blkbits;
> 
>  	/* check if thereserved journal credits might overflow */
> -	if (!(EXT4_I(mpd->inode)->i_flags & EXT4_EXTENTS_FL) &&
> -	     (nrblocks >= EXT4_MAX_TRANS_DATA))
> -		/*
> -		 * With noextent format we are limited by the journal
> -		 * credit available. Total credit needed to insert
> -		 * nrblocks contiguous blocks is dependent on the
> -		 * nrblocks. So limit nrblocks.
> -		 */
> -		goto flush_it;
> -
> +	if (!(EXT4_I(mpd->inode)->i_flags & EXT4_EXTENTS_FL)) {
> +		if (nrblocks >= EXT4_MAX_TRANS_DATA) {
> +			/*
> +			 * With noextent format we are limited by the journal
> +			 * credit available. Total credit needed to insert
> +			 * nrblocks contiguous blocks is dependent on the
> +			 * nrblocks. So limit nrblocks.
> +			 */
> +			goto flush_it;
> +		} else if ((nrblocks + (b_size >> mpd->inode->i_blkbits)) >
> +				EXT4_MAX_TRANS_DATA) {
> +			/*
> +			 * Adding the new buffer_head would make it cross the
> +			 * allowed limit for which we have journal credit
> +			 * reserved. So limit the new bh->b_size
> +			 */
> +			b_size = (EXT4_MAX_TRANS_DATA - nrblocks) <<
> +						mpd->inode->i_blkbits;
> +			/* we will do mpage_da_submit_io in the next loop */
> +		}
> +	}
>  	/*
>  	 * First block in the extent
>  	 */
>  	if (lbh->b_size == 0) {
>  		lbh->b_blocknr = logical;
> -		lbh->b_size = bh->b_size;
> +		lbh->b_size = b_size;
>  		lbh->b_state = bh->b_state & BH_FLAGS;
>  		return;
>  	}
> @@ -1939,7 +1951,7 @@ static void mpage_add_bh_to_extent(struct mpage_da_data *mpd,
>  	 * Can we merge the block to our big extent?
>  	 */
>  	if (logical == next && (bh->b_state & BH_FLAGS) == lbh->b_state) {
> -		lbh->b_size += bh->b_size;
> +		lbh->b_size += b_size;
>  		return;
>  	}
> 

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