On Tue, 2008-03-04 at 18:16 +0530, Aneesh Kumar K.V wrote:
> If the preallocated area is small zero out the full extent
> instead of splitting them. This should avoid the "write
> every alternate block" problem that could grow the number
> of extents dramatically.
>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
> ---
> fs/ext4/extents.c | 63 +++++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 files changed, 63 insertions(+), 0 deletions(-)
>
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index 839caf2..dcdf92a 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -2210,6 +2210,8 @@ static int ext4_ext_zeroout(struct inode *inode, struct ext4_extent *ex)
> return ret;
> }
>
> +#define EXT4_EXT_ZERO_LEN 7
> +
> /*
> * This function is called by ext4_ext_get_blocks() if someone tries to write
> * to an uninitialized extent. It may result in splitting the uninitialized
> @@ -2252,6 +2254,18 @@ static int ext4_ext_convert_to_initialized(handle_t *handle,
> err = ext4_ext_get_access(handle, inode, path + depth);
> if (err)
> goto out;
> + /* If extent has less than 2*EXT4_EXT_ZERO_LEN zerout directly */
Hmm, here this is range is extended to 2*EXT4_EXT_ZERO_LEN? I am a
little more biased to keep the threshold constant as EXT4_EXT_ZERO_LEN
around all places...
> + if (ee_len <= 2*EXT4_EXT_ZERO_LEN) {
> + err = ext4_ext_zeroout(inode, &orig_ex);
> + if (err)
> + goto fix_extent_len;
> + /* update the extent length and mark as initialized */
> + ex->ee_block = orig_ex.ee_block;
> + ex->ee_len = orig_ex.ee_len;
> + ext4_ext_store_pblock(ex, ext_pblock(&orig_ex));
> + ext4_ext_dirty(handle, inode, path + depth);
> + return le16_to_cpu(ex->ee_len);
> + }
>
> /* ex1: ee_block to iblock - 1 : uninitialized */
> if (iblock > ee_block) {
> @@ -2270,6 +2284,38 @@ static int ext4_ext_convert_to_initialized(handle_t *handle,
> /* ex3: to ee_block + ee_len : uninitialised */
> if (allocated > max_blocks) {
> unsigned int newdepth;
> + /* If extent has less than EXT4_EXT_ZERO_LEN zerout directly */
> + if (allocated <= EXT4_EXT_ZERO_LEN) {
> + /* Mark first half uninitialized.
> + * Mark second half initialized and zero out the
> + * initialized extent
> + */
> + ex->ee_block = orig_ex.ee_block;
> + ex->ee_len = cpu_to_le16(ee_len - allocated);
> + ext4_ext_mark_uninitialized(ex);
> + ext4_ext_store_pblock(ex, ext_pblock(&orig_ex));
> + ext4_ext_dirty(handle, inode, path + depth);
> +
> + ex3 = &newex;
> + ex3->ee_block = cpu_to_le32(iblock);
> + ext4_ext_store_pblock(ex3, newblock);
> + ex3->ee_len = cpu_to_le16(allocated);
> + err = ext4_ext_insert_extent(handle, inode, path, ex3);
> + if (err == -ENOSPC) {
> + err = ext4_ext_zeroout(inode, &orig_ex);
> + if (err)
> + goto fix_extent_len;
> + ex->ee_block = orig_ex.ee_block;
> + ex->ee_len = orig_ex.ee_len;
> + ext4_ext_store_pblock(ex, ext_pblock(&orig_ex));
> + ext4_ext_dirty(handle, inode, path + depth);
> + return le16_to_cpu(ex->ee_len);
> +
> + } else if (err)
> + goto fix_extent_len;
> +
> + return allocated;
> + }
> ex3 = &newex;
> ex3->ee_block = cpu_to_le32(iblock + max_blocks);
> ext4_ext_store_pblock(ex3, newblock + max_blocks);
> @@ -2318,6 +2364,23 @@ static int ext4_ext_convert_to_initialized(handle_t *handle,
> goto out;
> }
> allocated = max_blocks;
> +
> + /* If extent has less than EXT4_EXT_ZERO_LEN and we are trying
> + * to insert a extent in the middle zerout directly
> + * otherwise give the extent a chance to merge to left
> + */
> + if (le16_to_cpu(orig_ex.ee_len) <= EXT4_EXT_ZERO_LEN &&
> + iblock != ee_block) {
> + err = ext4_ext_zeroout(inode, &orig_ex);
> + if (err)
> + goto fix_extent_len;
> + /* update the extent length and mark as initialized */
> + ex->ee_block = orig_ex.ee_block;
> + ex->ee_len = orig_ex.ee_len;
> + ext4_ext_store_pblock(ex, ext_pblock(&orig_ex));
> + ext4_ext_dirty(handle, inode, path + depth);
> + return le16_to_cpu(ex->ee_len);
> + }
> }
> /*
> * If there was a change of depth as part of the
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