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
> +}
>
> - /*
> - * tree can be full, so it would need to grow in depth:
> - * we need one credit to modify old root, credits for
> - * new root will be added in split accounting
> - */
> - needed += 1;
> +/*
> + * How many index/leaf blocks need to change/allocate to modify nrblocks?
> + *
> + * if nrblocks are fit in a single extent (chunk flag is 1), then
> + * in the worse case, each tree level index/leaf need to be changed
> + * if the tree split due to insert a new extent, then the old tree
> + * index/leaf need to be updated too
> + *
> + * If the nrblocks are discontigous, they could cause
> + * the whole tree split more than once, but this is really rare.
> + */
> +static int ext4_ext_index_trans_blocks(struct inode *inode, int num, int chunk)
> +{
> + int index;
> + int depth = ext_depth(inode);
>
> - /*
> - * Index split can happen, we would need:
> - * allocate intermediate indexes (bitmap + group)
> - * + change two blocks at each level, but root (already included)
> - */
> - needed += (depth * 2) + (depth * 2);
>
> - /* any allocation modifies superblock */
> - needed += 1;
> + if (chunk)
> + index = depth * 2;
> + else
> + index = depth * 3;
>
> - return needed;
> + return index;
> }
>
....
-aneesh
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