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Date: Wed, 2 Mar 2011 14:21:22 +0800
From: Yongqiang Yang <xiaoqiangnk@...il.com>
To: Mingming Cao <cmm@...ibm.com>
Cc: Allison Henderson <achender@...ux.vnet.ibm.com>,
linux-ext4@...r.kernel.org
Subject: Re: [Ext4 punch hole 4/5] Ext4 Punch Hole Support: Enable Punch Hole
On Wed, Mar 2, 2011 at 10:34 AM, Yongqiang Yang <xiaoqiangnk@...il.com> wrote:
> On Wed, Mar 2, 2011 at 9:49 AM, Mingming Cao <cmm@...ibm.com> wrote:
>> 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?
> In ext4 FIEMAP, ext4_ext_walk_space() lookup requested block in extent
> tree firstly, and look next allocated block in extent-tree secondly,
> so if the block is not contained in the found extent, then lookup
> dirty pages starting from offset of the block in pagecahe. Next, find
> 1st mapped block in the found pages, if the 1st mapped block is not
> delayed and its block nr is less than or equal to the next allocated
> block, then a hole is found.
>
> To lookup a hole, just do as follows.
> 1. lookup block in the extent tree. if the found extent contains the
> request block, then no hole. otherwise, goto 2.
> 2. lookup the next allocated block.
> 3. lookup dirty pages in pagecache starting from offset of the block,
> then find the 1st mapped block. there are 3 cases.
> a. block number of 1st mapped block is greater than or equal to the
> next allocated block, then a hole is found.
> b. block number of 1st mapped block is less than the next allocated block,
> check delayed flag, a delayed extent is found.
c. should be contained in b case. block number of 1st mapped
block is less than the next allocated block, and greater than the
request block. A hole is found.
>
>>
>>> + /*
>>> + * 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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>>
>
>
>
> --
> Best Wishes
> Yongqiang Yang
>
--
Best Wishes
Yongqiang Yang
--
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