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Message-ID: <1304988702.2543.7.camel@mingming-laptop>
Date: Mon, 09 May 2011 17:51:42 -0700
From: Mingming Cao <cmm@...ibm.com>
To: Allison Henderson <achender@...ux.vnet.ibm.com>
Cc: Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: Re: [Ext4 punch hole 3/5 v7] Ext4 Punch Hole Support: Punch out
extents
On Sat, 2011-05-07 at 16:54 -0700, Allison Henderson wrote:
> v6->v7: Added optimization to while loop in ext4_ext_remove_space
> to limit the tree search to only the extents that need to be punched
> out
>
It indeed a optimization, not having to search entire tree:-)
Not blocking issue but we could do future optimization by making sure we
only punch out one extent at a time at high level so the while loop is
entirely removed. That could be future improvement.
>
> This patch modifies the truncate routines to support hole punching
> Below is a brief summary of the patches changes:
>
> - Added end param to ext_ext4_rm_leaf
> This function has been modified to accept an end parameter
> which enables it to punch holes in leafs instead of just
> truncating them.
>
> - Implemented the "remove head" case in the ext_remove_blocks routine
> This routine is used by ext_ext4_rm_leaf to remove the tail
> of an extent during a truncate. The new ext_ext4_rm_leaf
> routine will now also use it to remove the head of an extent in the
> case that the hole covers a region of blocks at the beginning
> of an extent.
>
> - Added "end" param to ext4_ext_remove_space routine
> This function has been modified to accept a stop parameter, which
> is passed through to ext4_ext_rm_leaf.
>
Overall I am fine with the patch. You could add
reviewed-by: Mingming Cao <cmm@...ibm.com>
> Signed-off-by: Allison Henderson <achender@...ibm.com>
> ---
> :100644 100644 e04faeb... 6dea243... M fs/ext4/extents.c
> fs/ext4/extents.c | 189 ++++++++++++++++++++++++++++++++++++++++++++++------
> 1 files changed, 167 insertions(+), 22 deletions(-)
>
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index e04faeb..6dea243 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -46,6 +46,13 @@
>
> #include <trace/events/ext4.h>
>
> +static int ext4_split_extent(handle_t *handle,
> + struct inode *inode,
> + struct ext4_ext_path *path,
> + struct ext4_map_blocks *map,
> + int split_flag,
> + int flags);
> +
> static int ext4_ext_truncate_extend_restart(handle_t *handle,
> struct inode *inode,
> int needed)
> @@ -2198,8 +2205,16 @@ static int ext4_remove_blocks(handle_t *handle, struct inode *inode,
> ext4_free_blocks(handle, inode, NULL, start, num, flags);
> } else if (from == le32_to_cpu(ex->ee_block)
> && to <= le32_to_cpu(ex->ee_block) + ee_len - 1) {
> - printk(KERN_INFO "strange request: removal %u-%u from %u:%u\n",
> - from, to, le32_to_cpu(ex->ee_block), ee_len);
> + /* head removal */
> + ext4_lblk_t num;
> + ext4_fsblk_t start;
> +
> + num = to - from;
> + start = ext4_ext_pblock(ex);
> +
> + ext_debug("free first %u blocks starting %llu\n", num, start);
> + ext4_free_blocks(handle, inode, 0, start, num, flags);
> +
> } else {
> printk(KERN_INFO "strange request: removal(2) "
> "%u-%u from %u:%u\n",
> @@ -2208,9 +2223,22 @@ static int ext4_remove_blocks(handle_t *handle, struct inode *inode,
> return 0;
> }
>
> +
> +/*
> + * ext4_ext_rm_leaf() Removes the extents associated with the
> + * blocks appearing between "start" and "end", and splits the extents
> + * if "start" and "end" appear in the same extent
> + *
> + * @handle: The journal handle
> + * @inode: The files inode
> + * @path: The path to the leaf
> + * @start: The first block to remove
> + * @end: The last block to remove
> + */
> static int
> ext4_ext_rm_leaf(handle_t *handle, struct inode *inode,
> - struct ext4_ext_path *path, ext4_lblk_t start)
> + struct ext4_ext_path *path, ext4_lblk_t start,
> + ext4_lblk_t end)
> {
> int err = 0, correct_index = 0;
> int depth = ext_depth(inode), credits;
> @@ -2221,6 +2249,7 @@ ext4_ext_rm_leaf(handle_t *handle, struct inode *inode,
> unsigned short ex_ee_len;
> unsigned uninitialized = 0;
> struct ext4_extent *ex;
> + struct ext4_map_blocks map;
>
> /* the header must be checked already in ext4_ext_remove_space() */
> ext_debug("truncate since %u in leaf\n", start);
> @@ -2250,31 +2279,95 @@ ext4_ext_rm_leaf(handle_t *handle, struct inode *inode,
> path[depth].p_ext = ex;
>
> a = ex_ee_block > start ? ex_ee_block : start;
> - b = ex_ee_block + ex_ee_len - 1 < EXT_MAX_BLOCK ?
> - ex_ee_block + ex_ee_len - 1 : EXT_MAX_BLOCK;
> + b = ex_ee_block+ex_ee_len - 1 < end ?
> + ex_ee_block+ex_ee_len - 1 : end;
>
> ext_debug(" border %u:%u\n", a, b);
>
> - if (a != ex_ee_block && b != ex_ee_block + ex_ee_len - 1) {
> - block = 0;
> - num = 0;
> - BUG();
> + /* If this extent is beyond the end of the hole, skip it */
> + if (end <= ex_ee_block) {
> + ex--;
> + ex_ee_block = le32_to_cpu(ex->ee_block);
> + ex_ee_len = ext4_ext_get_actual_len(ex);
> + continue;
> + } else if (a != ex_ee_block &&
> + b != ex_ee_block + ex_ee_len - 1) {
> + /*
> + * If this is a truncate, then this condition should
> + * never happen because at least one of the end points
> + * needs to be on the edge of the extent.
> + */
> + if (end == EXT_MAX_BLOCK) {
> + ext_debug(" bad truncate %u:%u\n",
> + start, end);
> + block = 0;
> + num = 0;
> + err = -EIO;
> + goto out;
> + }
> + /*
> + * else this is a hole punch, so the extent needs to
> + * be split since neither edge of the hole is on the
> + * extent edge
> + */
> + else{
> + map.m_pblk = ext4_ext_pblock(ex);
> + map.m_lblk = ex_ee_block;
> + map.m_len = b - ex_ee_block;
> +
> + err = ext4_split_extent(handle,
> + inode, path, &map, 0,
> + EXT4_GET_BLOCKS_PUNCH_OUT_EXT |
> + EXT4_GET_BLOCKS_PRE_IO);
> +
> + if (err < 0)
> + goto out;
> +
> + ex_ee_len = ext4_ext_get_actual_len(ex);
> +
> + b = ex_ee_block+ex_ee_len - 1 < end ?
> + ex_ee_block+ex_ee_len - 1 : end;
> +
> + /* Then remove tail of this extent */
> + block = ex_ee_block;
> + num = a - block;
> + }
> } else if (a != ex_ee_block) {
> /* remove tail of the extent */
> block = ex_ee_block;
> num = a - block;
> } else if (b != ex_ee_block + ex_ee_len - 1) {
> /* remove head of the extent */
> - block = a;
> - num = b - a;
> - /* there is no "make a hole" API yet */
> - BUG();
> + block = b;
> + num = ex_ee_block + ex_ee_len - b;
> +
> + /*
> + * If this is a truncate, this condition
> + * should never happen
> + */
> + if (end == EXT_MAX_BLOCK) {
> + ext_debug(" bad truncate %u:%u\n",
> + start, end);
> + err = -EIO;
> + goto out;
> + }
> } else {
> /* remove whole extent: excellent! */
> block = ex_ee_block;
> num = 0;
> - BUG_ON(a != ex_ee_block);
> - BUG_ON(b != ex_ee_block + ex_ee_len - 1);
> + if (a != ex_ee_block) {
> + ext_debug(" bad truncate %u:%u\n",
> + start, end);
> + err = -EIO;
> + goto out;
> + }
> +
> + if (b != ex_ee_block + ex_ee_len - 1) {
> + ext_debug(" bad truncate %u:%u\n",
> + start, end);
> + err = -EIO;
> + goto out;
> + }
> }
>
> /*
> @@ -2305,7 +2398,13 @@ ext4_ext_rm_leaf(handle_t *handle, struct inode *inode,
> if (num == 0) {
> /* this extent is removed; mark slot entirely unused */
> ext4_ext_store_pblock(ex, 0);
> - le16_add_cpu(&eh->eh_entries, -1);
> + } else if (block != ex_ee_block) {
> + /*
> + * If this was a head removal, then we need to update
> + * the physical block since it is now at a different
> + * location
> + */
> + ext4_ext_store_pblock(ex, ext4_ext_pblock(ex) + (b-a));
> }
>
> ex->ee_block = cpu_to_le32(block);
> @@ -2321,6 +2420,27 @@ ext4_ext_rm_leaf(handle_t *handle, struct inode *inode,
> if (err)
> goto out;
>
> + /*
> + * If the extent was completely released,
> + * we need to remove it from the leaf
> + */
> + if (num == 0) {
> + if (end != EXT_MAX_BLOCK) {
> + /*
> + * For hole punching, we need to scoot all the
> + * extents up when an extent is removed so that
> + * we dont have blank extents in the middle
> + */
> + memmove(ex, ex+1, (EXT_LAST_EXTENT(eh) - ex) *
> + sizeof(struct ext4_extent));
> +
> + /* Now get rid of the one at the end */
> + memset(EXT_LAST_EXTENT(eh), 0,
> + sizeof(struct ext4_extent));
> + }
> + le16_add_cpu(&eh->eh_entries, -1);
> + }
> +
> ext_debug("new extent: %u:%u:%llu\n", block, num,
> ext4_ext_pblock(ex));
> ex--;
> @@ -2361,13 +2481,16 @@ ext4_ext_more_to_rm(struct ext4_ext_path *path)
> return 1;
> }
>
> -static int ext4_ext_remove_space(struct inode *inode, ext4_lblk_t start)
> +static int ext4_ext_remove_space(struct inode *inode, ext4_lblk_t start,
> + ext4_lblk_t end)
> {
> struct super_block *sb = inode->i_sb;
> int depth = ext_depth(inode);
> struct ext4_ext_path *path;
> + struct ext4_extent_header *eh;
> + struct ext4_extent *ex;
> handle_t *handle;
> - int i, err;
> + int i, err, last_extent;
>
> ext_debug("truncate since %u\n", start);
>
> @@ -2400,12 +2523,32 @@ again:
> while (i >= 0 && err == 0) {
> if (i == depth) {
> /* this is leaf block */
> - err = ext4_ext_rm_leaf(handle, inode, path, start);
> +
> + eh = path[depth].p_hdr;
> + if (!eh)
> + eh = ext_block_hdr(path[depth].p_bh);
> + if (unlikely(eh == NULL)) {
> + EXT4_ERROR_INODE(inode,
> + "path[%d].p_hdr == NULL", depth);
> + err = -EIO;
> + break;
> + }
> +
> + ex = EXT_FIRST_EXTENT(eh);
> + last_extent = ex != NULL ?
> + le32_to_cpu(ex->ee_block) >= start : 0;
> +
> + err = ext4_ext_rm_leaf(handle, inode, path,
> + start, end);
> /* root level has p_bh == NULL, brelse() eats this */
> brelse(path[i].p_bh);
> path[i].p_bh = NULL;
> i--;
> - continue;
> +
> + if (last_extent)
> + break;
> + else
> + continue;
> }
>
> /* this is index block */
> @@ -2429,7 +2572,9 @@ again:
> ext_debug("level %d - index, first 0x%p, cur 0x%p\n",
> i, EXT_FIRST_INDEX(path[i].p_hdr),
> path[i].p_idx);
> - if (ext4_ext_more_to_rm(path + i)) {
> + if (ext4_ext_more_to_rm(path + i) &&
> + (path[i].p_idx->ei_block < end)) {
> +
> struct buffer_head *bh;
> /* go to the next level */
> ext_debug("move to level %d (block %llu)\n",
> @@ -3445,7 +3590,7 @@ void ext4_ext_truncate(struct inode *inode)
>
> last_block = (inode->i_size + sb->s_blocksize - 1)
> >> EXT4_BLOCK_SIZE_BITS(sb);
> - err = ext4_ext_remove_space(inode, last_block);
> + err = ext4_ext_remove_space(inode, last_block, EXT_MAX_BLOCK);
>
> /* In a multi-transaction truncate, we only make the final
> * transaction synchronous.
--
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