From: Lukas Czerner Subject: Re: [PATCH 1/3 v2] ext4: Rewrite punch hole to use ext4_ext_remove_space() Date: Wed, 21 Mar 2012 08:25:45 +0100 (CET) Message-ID: References: <1332181175-10503-1-git-send-email-lczerner@redhat.com> <4F681BBF.2070107@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Cc: Lukas Czerner , linux-ext4@vger.kernel.org, tytso@mit.edu To: Allison Henderson Return-path: Received: from mx1.redhat.com ([209.132.183.28]:65158 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753595Ab2CUHZv (ORCPT ); Wed, 21 Mar 2012 03:25:51 -0400 In-Reply-To: <4F681BBF.2070107@linux.vnet.ibm.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Mon, 19 Mar 2012, Allison Henderson wrote: > On 03/19/2012 11:24 AM, Lukas Czerner wrote: > > Hi Allison, > > > > I just want to let you know that I have rebased your patches to > > allow punching hole past i_size, but I am going to send it as a separate > > series hopefully this week. I need to solve the problem with cleaning > > EOFBLOCKS_FL flag properly first. So just you know that you do not need > > to worry about those. > > > > Thanks! > > -Lukas > > Alrighty then, sounds good. Also, I looked through the v2 set and it looks > good to me. Thx for the all the clean up :) > > Allison Henderson no problem, I just sent it out to the list so please let me know if you're ok with it. Thanks! -Lukas > > > > > On Mon, 19 Mar 2012, Lukas Czerner wrote: > > > > > This commit rewrites ext4 punch hole implementation to use > > > ext4_ext_remove_space() instead of its home gown way of doing this via > > > ext4_ext_map_blocks(). There are several reasons for changing this. > > > > > > Firstly it is quite non obvious that punching hole needs to > > > ext4_ext_map_blocks() to punch a hole, especially given that this > > > function should map blocks, not unmap it. It also required a lot of new > > > code in ext4_ext_map_blocks(). > > > > > > Secondly the design of it is not very effective. The reason is that we > > > are trying to punch out blocks in ext4_ext_punch_hole() in opposite > > > direction than in ext4_ext_rm_leaf() which causes the ext4_ext_rm_leaf() > > > to iterate through the whole tree from the end to the start to find the > > > requested extent for every extent we are going to punch out. > > > > > > And finally the current implementation does not use the existing code, > > > but bring a lot of new code, which is IMO unnecessary since there > > > already is some infrastructure we can use. Specifically > > > ext4_ext_remove_space(). > > > > > > This commit changes ext4_ext_remove_space() to accept 'end' parameter so > > > we can not only truncate to the end of file, but also remove the space > > > in the middle of the file (punch a hole). Moreover, because the last > > > block to punch out, might be in the middle of the extent, we have to > > > split the extent at 'end + 1' so ext4_ext_rm_leaf() can easily either > > > remove the whole fist part of split extent, or change its size. > > > > > > ext4_ext_remove_space() is then used to actually remove the space > > > (extents) from within the hole, instead of ext4_ext_map_blocks(). > > > > > > Note that this also fix the issue with punch hole, where we would forget > > > to remove empty index blocks from the extent tree, resulting in double > > > free block error and file system corruption. This is simply because we > > > now use different code path, where this problem does not exist. > > > > > > This has been tested with fsx running for several days and xfstests, > > > plus xfstest #251 with '-o discard' run on the loop image (which > > > converts discard requestes into punch hole to the backing file). All of > > > it on 1K and 4K file system block size. > > > > > > Signed-off-by: Lukas Czerner > > > --- > > > v2: Change condition to distinct punch_hole from truncate in > > > ext4_ext_remove_space() > > > > > > fs/ext4/extents.c | 170 > > > +++++++++++++++++++++++++++------------------------- > > > 1 files changed, 88 insertions(+), 82 deletions(-) > > > > > > diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c > > > index 74f23c2..522f429 100644 > > > --- a/fs/ext4/extents.c > > > +++ b/fs/ext4/extents.c > > > @@ -44,6 +44,14 @@ > > > > > > #include > > > > > > +/* > > > + * used by extent splitting. > > > + */ > > > +#define EXT4_EXT_MAY_ZEROOUT 0x1 /* safe to zeroout if split fails > > > \ > > > + due to ENOSPC */ > > > +#define EXT4_EXT_MARK_UNINIT1 0x2 /* mark first half uninitialized > > > */ > > > +#define EXT4_EXT_MARK_UNINIT2 0x4 /* mark second half uninitialized > > > */ > > > + > > > static int ext4_split_extent(handle_t *handle, > > > struct inode *inode, > > > struct ext4_ext_path *path, > > > @@ -51,6 +59,13 @@ static int ext4_split_extent(handle_t *handle, > > > int split_flag, > > > int flags); > > > > > > +static int ext4_split_extent_at(handle_t *handle, > > > + struct inode *inode, > > > + struct ext4_ext_path *path, > > > + ext4_lblk_t split, > > > + int split_flag, > > > + int flags); > > > + > > > static int ext4_ext_truncate_extend_restart(handle_t *handle, > > > struct inode *inode, > > > int needed) > > > @@ -2308,7 +2323,7 @@ ext4_ext_rm_leaf(handle_t *handle, struct inode > > > *inode, > > > struct ext4_extent *ex; > > > > > > /* the header must be checked already in ext4_ext_remove_space() */ > > > - ext_debug("truncate since %u in leaf\n", start); > > > + ext_debug("truncate since %u in leaf to %u\n", start, end); > > > if (!path[depth].p_hdr) > > > path[depth].p_hdr = ext_block_hdr(path[depth].p_bh); > > > eh = path[depth].p_hdr; > > > @@ -2343,7 +2358,7 @@ ext4_ext_rm_leaf(handle_t *handle, struct inode > > > *inode, > > > ext_debug(" border %u:%u\n", a, b); > > > > > > /* If this extent is beyond the end of the hole, skip it */ > > > - if (end<= ex_ee_block) { > > > + if (end< ex_ee_block) { > > > ex--; > > > ex_ee_block = le32_to_cpu(ex->ee_block); > > > ex_ee_len = ext4_ext_get_actual_len(ex); > > > @@ -2482,7 +2497,8 @@ 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); > > > @@ -2491,7 +2507,7 @@ static int ext4_ext_remove_space(struct inode > > > *inode, ext4_lblk_t start) > > > handle_t *handle; > > > int i, err; > > > > > > - ext_debug("truncate since %u\n", start); > > > + ext_debug("truncate since %u to %u\n", start, end); > > > > > > /* probably first extent we're gonna free will be last in block */ > > > handle = ext4_journal_start(inode, depth + 1); > > > @@ -2504,6 +2520,61 @@ again: > > > trace_ext4_ext_remove_space(inode, start, depth); > > > > > > /* > > > + * Check if we are removing extents inside the extent tree. If that > > > + * is the case, we are going to punch a hole inside the extent tree > > > + * so we have to check whether we need to split the extent covering > > > + * the last block to remove so we can easily remove the part of it > > > + * in ext4_ext_rm_leaf(). > > > + */ > > > + if (end< EXT_MAX_BLOCKS - 1) { > > > + struct ext4_extent *ex; > > > + ext4_lblk_t ee_block; > > > + > > > + /* find extent for this block */ > > > + path = ext4_ext_find_extent(inode, end, NULL); > > > + if (IS_ERR(path)) { > > > + ext4_journal_stop(handle); > > > + return PTR_ERR(path); > > > + } > > > + depth = ext_depth(inode); > > > + ex = path[depth].p_ext; > > > + if (!ex) > > > + goto cont; > > > + > > > + ee_block = le32_to_cpu(ex->ee_block); > > > + > > > + /* > > > + * See if the last block is inside the extent, if so split > > > + * the extent at 'end' block so we can easily remove the > > > + * tail of the first part of the split extent in > > > + * ext4_ext_rm_leaf(). > > > + */ > > > + if (end>= ee_block&& > > > + end< ee_block + ext4_ext_get_actual_len(ex) - 1) { > > > + int split_flag = 0; > > > + > > > + if (ext4_ext_is_uninitialized(ex)) > > > + split_flag = EXT4_EXT_MARK_UNINIT1 | > > > + EXT4_EXT_MARK_UNINIT2; > > > + > > > + /* > > > + * Split the extent in two so that 'end' is the last > > > + * block in the first new extent > > > + */ > > > + err = ext4_split_extent_at(handle, inode, path, > > > + end + 1, split_flag, > > > + EXT4_GET_BLOCKS_PRE_IO | > > > + > > > EXT4_GET_BLOCKS_PUNCH_OUT_EXT); > > > + > > > + if (err< 0) > > > + goto out; > > > + } > > > + ext4_ext_drop_refs(path); > > > + kfree(path); > > > + } > > > +cont: > > > + > > > + /* > > > * We start scanning from right side, freeing all the blocks > > > * after i_size and walking into the tree depth-wise. > > > */ > > > @@ -2515,6 +2586,7 @@ again: > > > } > > > 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; > > > @@ -2526,7 +2598,7 @@ again: > > > /* this is leaf block */ > > > err = ext4_ext_rm_leaf(handle, inode, path, > > > &partial_cluster, start, > > > - EXT_MAX_BLOCKS - 1); > > > + end); > > > /* root level has p_bh == NULL, brelse() eats this */ > > > brelse(path[i].p_bh); > > > path[i].p_bh = NULL; > > > @@ -2709,14 +2781,6 @@ static int ext4_ext_zeroout(struct inode *inode, > > > struct ext4_extent *ex) > > > } > > > > > > /* > > > - * used by extent splitting. > > > - */ > > > -#define EXT4_EXT_MAY_ZEROOUT 0x1 /* safe to zeroout if split fails > > > \ > > > - due to ENOSPC */ > > > -#define EXT4_EXT_MARK_UNINIT1 0x2 /* mark first half uninitialized > > > */ > > > -#define EXT4_EXT_MARK_UNINIT2 0x4 /* mark second half uninitialized > > > */ > > > - > > > -/* > > > * ext4_split_extent_at() splits an extent at given block. > > > * > > > * @handle: the journal handle > > > @@ -4228,7 +4292,7 @@ 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_BLOCKS - 1); > > > > > > /* In a multi-transaction truncate, we only make the final > > > * transaction synchronous. > > > @@ -4705,14 +4769,12 @@ int ext4_ext_punch_hole(struct file *file, loff_t > > > offset, loff_t length) > > > { > > > struct inode *inode = file->f_path.dentry->d_inode; > > > struct super_block *sb = inode->i_sb; > > > - struct ext4_ext_cache cache_ex; > > > - ext4_lblk_t first_block, last_block, num_blocks, iblock, max_blocks; > > > + ext4_lblk_t first_block, stop_block; > > > struct address_space *mapping = inode->i_mapping; > > > - struct ext4_map_blocks map; > > > handle_t *handle; > > > loff_t first_page, last_page, page_len; > > > loff_t first_page_offset, last_page_offset; > > > - int ret, credits, blocks_released, err = 0; > > > + int credits, err = 0; > > > > > > /* No need to punch hole beyond i_size */ > > > if (offset>= inode->i_size) > > > @@ -4728,10 +4790,6 @@ int ext4_ext_punch_hole(struct file *file, loff_t > > > offset, loff_t length) > > > offset; > > > } > > > > > > - first_block = (offset + sb->s_blocksize - 1)>> > > > - EXT4_BLOCK_SIZE_BITS(sb); > > > - last_block = (offset + length)>> EXT4_BLOCK_SIZE_BITS(sb); > > > - > > > first_page = (offset + PAGE_CACHE_SIZE - 1)>> PAGE_CACHE_SHIFT; > > > last_page = (offset + length)>> PAGE_CACHE_SHIFT; > > > > > > @@ -4810,7 +4868,6 @@ int ext4_ext_punch_hole(struct file *file, loff_t > > > offset, loff_t length) > > > } > > > } > > > > > > - > > > /* > > > * If i_size is contained in the last page, we need to > > > * unmap and zero the partial page after i_size > > > @@ -4830,73 +4887,22 @@ int ext4_ext_punch_hole(struct file *file, loff_t > > > offset, loff_t length) > > > } > > > } > > > > > > + first_block = (offset + sb->s_blocksize - 1)>> > > > + EXT4_BLOCK_SIZE_BITS(sb); > > > + stop_block = (offset + length)>> EXT4_BLOCK_SIZE_BITS(sb); > > > + > > > /* If there are no blocks to remove, return now */ > > > - if (first_block>= last_block) > > > + if (first_block>= stop_block) > > > goto out; > > > > > > down_write(&EXT4_I(inode)->i_data_sem); > > > ext4_ext_invalidate_cache(inode); > > > ext4_discard_preallocations(inode); > > > > > > - /* > > > - * Loop over all the blocks and identify blocks > > > - * that need to be punched out > > > - */ > > > - iblock = first_block; > > > - blocks_released = 0; > > > - while (iblock< last_block) { > > > - max_blocks = last_block - iblock; > > > - num_blocks = 1; > > > - memset(&map, 0, sizeof(map)); > > > - map.m_lblk = iblock; > > > - map.m_len = max_blocks; > > > - ret = ext4_ext_map_blocks(handle, inode,&map, > > > - EXT4_GET_BLOCKS_PUNCH_OUT_EXT); > > > - > > > - if (ret> 0) { > > > - blocks_released += ret; > > > - num_blocks = ret; > > > - } else if (ret == 0) { > > > - /* > > > - * If map blocks could not find the block, > > > - * then it is in a hole. If the hole was > > > - * not already cached, then map blocks should > > > - * put it in the cache. So we can get the hole > > > - * out of the cache > > > - */ > > > - memset(&cache_ex, 0, sizeof(cache_ex)); > > > - if ((ext4_ext_check_cache(inode, iblock,&cache_ex))&& > > > - !cache_ex.ec_start) { > > > + err = ext4_ext_remove_space(inode, first_block, stop_block - 1); > > > > > > - /* The hole is cached */ > > > - num_blocks = cache_ex.ec_block + > > > - cache_ex.ec_len - iblock; > > > - > > > - } else { > > > - /* The block could not be identified */ > > > - err = -EIO; > > > - break; > > > - } > > > - } else { > > > - /* Map blocks error */ > > > - err = ret; > > > - break; > > > - } > > > - > > > - if (num_blocks == 0) { > > > - /* This condition should never happen */ > > > - ext_debug("Block lookup failed"); > > > - err = -EIO; > > > - break; > > > - } > > > - > > > - iblock += num_blocks; > > > - } > > > - > > > - if (blocks_released> 0) { > > > - ext4_ext_invalidate_cache(inode); > > > - ext4_discard_preallocations(inode); > > > - } > > > + ext4_ext_invalidate_cache(inode); > > > + ext4_discard_preallocations(inode); > > > > > > if (IS_SYNC(inode)) > > > ext4_handle_sync(handle); > > > > > > > --