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Date: Tue, 01 Mar 2011 17:49:28 -0800
From: Mingming Cao <cmm@...ibm.com>
To: Allison Henderson <achender@...ux.vnet.ibm.com>
Cc: linux-ext4@...r.kernel.org
Subject: Re: [Ext4 punch hole 4/5] Ext4 Punch Hole Support: Enable Punch
Hole
On Mon, 2011-02-28 at 20:09 -0700, Allison Henderson wrote:
> This patch adds the new "ext4_punch_hole" "ext4_ext_punch_hole" routines.
>
> fallocate has been modified to call ext4_punch_hole when the punch hole
> flag is passed. At the moment, we only support punching holes in
> extents, so this routine is pretty much a wrapper for the ext4_ext_punch_hole
> routine.
>
> The ext4_ext_punch_hole routine zeros out the pages that are
> covered by the hole. The blocks to be punched out
> are then identified as mapped, delayed, or already punched out.
> The blocks that mapped are the converted to into uninitialized
> extents. The blocks are then punched out using the
> "ext4_ext_release_blocks" routine.
>
All right, I mainly looked at the punch hole over a hole or delayed
allocation handling part...so my comments below...
> Some minor utility functions have also been added.
> A new ext4_ext_lookup_hole routine is used by
> ext4_ext_punch_hole to check if a range of blocks
> have already been punched out.
>
> A new ext4_ext_test_block_flag has also been
> added to identify the state of a block (ie mapped,
> delayed, ect)
>
> Signed-off-by: Allison Henderson <achender@...ibm.com>
> ---
> :100644 100644 43a5772... aeb86d6... M fs/ext4/ext4.h
> :100644 100644 efbc3ef... 5713258... M fs/ext4/extents.c
> :100644 100644 28c9137... 493c908... M fs/ext4/inode.c
> fs/ext4/ext4.h | 2 +
> fs/ext4/extents.c | 321 ++++++++++++++++++++++++++++++++++++++++++++++++++++-
> fs/ext4/inode.c | 26 +++++
> 3 files changed, 345 insertions(+), 4 deletions(-)
>
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 43a5772..aeb86d6 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -1729,6 +1729,7 @@ extern int ext4_change_inode_journal_flag(struct inode *, int);
> extern int ext4_get_inode_loc(struct inode *, struct ext4_iloc *);
> extern int ext4_can_truncate(struct inode *inode);
> extern void ext4_truncate(struct inode *);
> +extern long ext4_punch_hole(struct inode *inode,loff_t offset, loff_t length);
> extern int ext4_truncate_restart_trans(handle_t *, struct inode *, int nblocks);
> extern void ext4_set_inode_flags(struct inode *);
> extern void ext4_get_inode_flags(struct ext4_inode_info *);
> @@ -2066,6 +2067,7 @@ extern int ext4_ext_index_trans_blocks(struct inode *inode, int nrblocks,
> extern int ext4_ext_map_blocks(handle_t *handle, struct inode *inode,
> struct ext4_map_blocks *map, int flags);
> extern void ext4_ext_truncate(struct inode *);
> +extern void ext4_ext_punch_hole(struct inode *inode, loff_t offset, loff_t length);
> extern void ext4_ext_init(struct super_block *);
> extern void ext4_ext_release(struct super_block *);
> extern long ext4_fallocate(struct file *file, int mode, loff_t offset,
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index efbc3ef..5713258 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -2776,6 +2776,154 @@ out:
> }
>
> /*
> + * lookup_hole()
> + * Returns the numbers of consecutive blocks starting at "start"
> + * that are not contained within an extent
> + */
The lookup hole path, IMHO, could be a special flag pass to
ext4_map_blocks(), reuse existing code, rather adding a new function
directly inspecting the inode's allocation tree from there.:)
> +static int ext4_ext_lookup_hole(struct inode *inode, ext4_lblk_t start){
> + 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;
> + struct buffer_head *bh;
> + ext4_lblk_t last_block;
> + handle_t *handle;
> + int i, err;
> +
> + ext_debug("lookup hole since %u\n", start);
> +
> + /* Make sure start is valid */
> + last_block = inode->i_size >> EXT4_BLOCK_SIZE_BITS(sb);
> + if(start >= last_block)
> + return -EIO;
> +
> + handle = ext4_journal_start(inode, depth + 1);
> + if (IS_ERR(handle))
> + return PTR_ERR(handle);
> +
> + /*
> + * We start scanning from right side, looking for
> + * the left most block contained in the leaf, and
> + * stopping when "start" is crossed.
> + */
> + depth = ext_depth(inode);
> + path = kzalloc(sizeof(struct ext4_ext_path) * (depth + 1), GFP_NOFS);
> + if (path == NULL) {
> + ext4_journal_stop(handle);
> + return -ENOMEM;
> + }
> + path[0].p_depth = depth;
> + path[0].p_hdr = ext_inode_hdr(inode);
> + if (ext4_ext_check(inode, path[0].p_hdr, depth)) {
> + err = -EIO;
> + goto out;
> + }
> + i = err = 0;
> +
> + while (i >= 0 && err == 0) {
> + if (i == depth) {
> + /* this is leaf block */
> +
> + eh = path[i].p_hdr;
> + if (eh != NULL){
> + if (eh->eh_entries == 0){
> + err = -EIO;
> + goto out;
> + }
> +
> + ex = EXT_LAST_EXTENT(eh);
> + while (ex != NULL && ex >= EXT_FIRST_EXTENT(eh)){
> +
> + /*
> + * If the entire extent apears before start
> + * then we have passed the hole.
> + */
> + if(ex->ee_block + ex->ee_len <= start)
> + goto out;
> +
> + /*
> + * If the start of the extent appears after
> + * or on start, then mark this as the edge
> + * of the hole
> + */
> + if(ex->ee_block >= start)
> + last_block = ex->ee_block;
> +
> + /*
> + * If the extent contains start, then there
> + * is no hole.
> + */
> + else if(ex->ee_block + ex->ee_len > start){
> + last_block = start;
> + goto out;
> + }
> +
> + ex--;
> + }
> + }
> +
> + /* root level has p_bh == NULL, brelse() eats this */
> + brelse(path[i].p_bh);
> + path[i].p_bh = NULL;
> + i--;
> + continue;
> + }
> +
> + /* this is index block */
> + if (!path[i].p_hdr)
> + path[i].p_hdr = ext_block_hdr(path[i].p_bh);
> +
> + if (!path[i].p_idx) {
> + /* this level hasn't been touched yet */
> + path[i].p_idx = EXT_LAST_INDEX(path[i].p_hdr);
> + path[i].p_block = le16_to_cpu(path[i].p_hdr->eh_entries)+1;
> + ext_debug("init index ptr: hdr 0x%p, num %d\n",
> + path[i].p_hdr,
> + le16_to_cpu(path[i].p_hdr->eh_entries));
> + }
> + else {
> + /* we were already here, see at next index */
> + path[i].p_idx--;
> + }
> +
> + ext_debug("level %d - index, first 0x%p, cur 0x%p\n",
> + i, EXT_FIRST_INDEX(path[i].p_hdr),
> + path[i].p_idx);
> +
> + /* go to the next level */
> + ext_debug("move to level %d (block %llu)\n",
> + i + 1, ext4_idx_pblock(path[i].p_idx));
> + memset(path + i + 1, 0, sizeof(*path));
> + bh = sb_bread(sb, ext4_idx_pblock(path[i].p_idx));
> + if (!bh) {
> + err = -EIO;
> + break;
> + }
> + if (WARN_ON(i + 1 > depth)) {
> + err = -EIO;
> + break;
> + }
> + if (ext4_ext_check(inode, ext_block_hdr(bh), depth - i - 1)) {
> + err = -EIO;
> + break;
> + }
> +
> + path[i + 1].p_bh = bh;
> +
> + i++;
> +
> + }
> +out:
> + ext4_ext_drop_refs(path);
> + kfree(path);
> + ext4_journal_stop(handle);
> +
> + return err ? err : last_block - start;
> +
> +}
> +
> +/*
> * called at mount time
> */
> void ext4_ext_init(struct super_block *sb)
> @@ -4029,6 +4177,172 @@ next:
> return ret;
> }
>
> +/*
> + * ext4_ext_test_block_flag
> + * Tests the buffer head associated with the given block
> + * to see if the state contains flag
> + *
> + * @inode: The inode of the given file
> + * @block: The block to test
> + * @flag: The flag to check for
> + *
> + * Returns 0 on sucess or negative on err
> + */
> +static int ext4_ext_test_block_flag(struct inode *inode, ext4_lblk_t block, enum bh_state_bits flag){
> + struct buffer_head *bh;
> + struct page *page;
> + struct address_space *mapping = inode->i_mapping;
> + loff_t block_offset;
> + int i, ret;
> + unsigned long flag_mask = 1 << flag;
> +
> + block_offset = block << EXT4_BLOCK_SIZE_BITS(inode->i_sb);
> + page = find_or_create_page(mapping, block_offset >> PAGE_CACHE_SHIFT,
> + mapping_gfp_mask(mapping) & ~__GFP_FS);
> +
> + if (!page)
> + return -EIO;
> +
> + if (!page_has_buffers(page))
> + create_empty_buffers(page, EXT4_BLOCK_SIZE(inode->i_sb), 0);
> +
> + /* advance to the buffer that has the block offset */
> + bh = page_buffers(page);
> + for (i = 0; i < block_offset; i+=EXT4_BLOCK_SIZE(inode->i_sb)) {
> + bh = bh->b_this_page;
> + }
> +
> + if(bh->b_state & flag_mask)
> + ret = 0;
> + else
> + ret = -1;
> +
> + unlock_page(page);
> + page_cache_release(page);
> +
> + return ret;
> +
> +}
> +
> +/*
> + * ext4_ext_punch_hole
> + *
> + * Punches a hole of "length" bytes in a file starting
> + * at byte "offset"
> + *
> + * @inode: The inode of the file to punch a hole in
> + * @offset: The starting byte offset of the hole
> + * @length: The length of the hole
> + *
> + */
> +void ext4_ext_punch_hole(struct inode *inode, loff_t offset, loff_t length)
> +{
> + struct super_block *sb = inode->i_sb;
> + ext4_lblk_t first_block, last_block, num_blocks, iblock = 0;
> + struct address_space *mapping = inode->i_mapping;
> + struct ext4_map_blocks map;
> + handle_t *handle;
> + loff_t first_block_offset, last_block_offset, block_len;
> + int get_blocks_flags, err, ret = 0;
> +
> + first_block = (offset + sb->s_blocksize - 1)
> + >> EXT4_BLOCK_SIZE_BITS(sb);
> + last_block = (offset+length) >> EXT4_BLOCK_SIZE_BITS(sb);
> +
> + first_block_offset = first_block << EXT4_BLOCK_SIZE_BITS(sb);
> + last_block_offset = last_block << EXT4_BLOCK_SIZE_BITS(sb);
> +
> + err = ext4_writepage_trans_blocks(inode);
> + handle = ext4_journal_start(inode, err);
> + if (IS_ERR(handle))
> + return;
> +
> + /*
> + * Now we need to zero out the un block aligned data.
> + * If the file is smaller than a block, just
> + * zero out the middle and return
> + */
> + if(first_block > last_block)
> + ext4_block_zero_page_range(handle, mapping, offset, length);
> + else{
> + /* zero out the head of the hole before the first block */
> + block_len = first_block_offset - offset;
> + if(block_len > 0)
> + ext4_block_zero_page_range(handle, mapping, offset, block_len);
> +
> + /* zero out the tail of the hole after the last block */
> + block_len = offset + length - last_block_offset;
> + if(block_len > 0)
> + ext4_block_zero_page_range(handle, mapping,
> + last_block_offset, block_len);
> + }
> +
> + /* If there are no blocks to remove, return now */
> + if(first_block >= last_block){
> + ext4_journal_stop(handle);
> + return;
> + }
> +
> + /* Clear pages associated with the hole */
> + if (mapping->nrpages)
> + invalidate_inode_pages2_range(mapping, offset >> PAGE_CACHE_SHIFT,
> + (offset+length) >> PAGE_CACHE_SHIFT );
> +
> +
> + /* Loop over all the blocks and identify blocks that need to be punched out */
> + iblock = first_block;
> + while(iblock < last_block){
> + map.m_lblk = iblock;
> + map.m_len = last_block - iblock;
> + ret = ext4_map_blocks(handle, inode, &map, 0);
> +
> + /* If the blocks are mapped, release them */
> + if(ret > 0){
> + num_blocks = ret;
> + ext4_ext_convert_blocks_uninit(inode, handle, iblock, num_blocks);
> + ext4_ext_release_blocks(inode, iblock, iblock+num_blocks);
> + goto next;
> + }
> +
> + /*
> + * If they are not mapped
> + * check to see if they are punched out
> + */
> + ret = ext4_ext_lookup_hole(inode, iblock);
> + if(ret > 0){
> + num_blocks = ret;
> + goto next;
> + }
> +
I am wondering how ext4 FIEMAP handles hole lookup more efficently?
> + /*
> + * If the block could not be mapped, and
> + * its not already punched out,
> + * check to see if the block is delayed
> + */
> + if(ext4_ext_test_block_flag(inode, iblock, BH_Delay) == 0){
> + get_blocks_flags = EXT4_GET_BLOCKS_CREATE | EXT4_GET_BLOCKS_DELALLOC_RESERVE;
Ah... the flags, could you check it again? We might get this wrong.
EXT4_GET_BLOCKS_CREATE | EXT4_GET_BLOCKS_DELALLOC_RESERVE?
these combination means we are plan to do block allocation via delayed
allocation path. From inode.c. this flag is aim to tell block allocation
to takes care of block reservation/release for delayed allocation patch.
we should at least turn off the create flag, and check if
EXT4_GET_BLOCKS_DELALLOC_RESERVE is also used for delayed extents look
up also? Maybe I missed something.
> + ret = ext4_map_blocks(handle, inode, &map, get_blocks_flags);
> + /* If the blocks are found, release them */
> +
> + if(ret > 0){
> + num_blocks = ret;
> + ext4_ext_release_blocks(inode, iblock, iblock+num_blocks);
> + goto next;
> + }
ext4_ext_release_blocks() is freeing up real storage on disk. For
delayed allocation case, there are no blocks allocated yet. We should
call ext4_da_release_space() or similar to free up the blocks reserved
by delayed allocation.
> + }
> +
> + /* If the block cannot be identified, just skip it */
> + num_blocks = 1;
> +
> +next:
> + iblock+=num_blocks;
> + }
> + ext4_mark_inode_dirty(handle, inode);
> +
> + ext4_journal_stop(handle);
> +
> +}
> +
>
> static void ext4_falloc_update_inode(struct inode *inode,
> int mode, loff_t new_size, int update_ctime)
> @@ -4079,10 +4393,6 @@ long ext4_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
> struct ext4_map_blocks map;
> unsigned int credits, blkbits = inode->i_blkbits;
>
> - /* We only support the FALLOC_FL_KEEP_SIZE mode */
> - if (mode & ~FALLOC_FL_KEEP_SIZE)
> - return -EOPNOTSUPP;
> -
> /*
> * currently supporting (pre)allocate mode for extent-based
> * files _only_
> @@ -4090,6 +4400,9 @@ long ext4_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
> if (!(ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)))
> return -EOPNOTSUPP;
>
> + if (mode & FALLOC_FL_PUNCH_HOLE)
> + return ext4_punch_hole(inode, offset, len);
> +
so for other than the three existing mode, we should also return
EOPNOTSUPP too, isn't?
> map.m_lblk = offset >> blkbits;
> /*
> * We can't just convert len to max_blocks because
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 28c9137..493c908 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -4487,6 +4487,32 @@ int ext4_can_truncate(struct inode *inode)
> }
>
> /*
> + * ext4_punch_hole: punches a hole in a file by releaseing the blocks
> + * associated with the given offset and length
> + *
> + * @inode: File inode
> + * @offset: The offset where the hole will begin
> + * @len: The length of the hole
> + *
> + * Returns: 0 on sucess or negative on failure
> + */
> +
> +long ext4_punch_hole(struct inode *inode, loff_t offset, loff_t length)
> +{
> +
> + if (!S_ISREG(inode->i_mode)==1)
> + return -ENOTSUPP;
> +
> + if (!ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
> + //TODO: Add support for non extent hole punching
> + return -ENOTSUPP;
> + }
> +
> + ext4_ext_punch_hole(inode, offset, length);
> + return 0;
> +}
> +
> +/*
> * ext4_truncate()
> *
> * We block out ext4_get_block() block instantiations across the entire
--
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