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Message-ID: <AANLkTikrKpKUhJ=uW0JYmi1t4j1qZw5F4AKGPosn57by@mail.gmail.com>
Date: Tue, 1 Mar 2011 11:30:06 +0200
From: Amir Goldstein <amir73il@...il.com>
To: Allison Henderson <achender@...ux.vnet.ibm.com>
Cc: Ext4 Developers List <linux-ext4@...r.kernel.org>,
Eric Sandeen <sandeen@...hat.com>
Subject: Re: [Ext4 punch hole 1/5] Ext4 Punch Hole Support: Convert Blocks to
Uninit Exts
On Tue, Mar 1, 2011 at 5:08 AM, Allison Henderson
<achender@...ux.vnet.ibm.com> wrote:
> Hi All!
>
> This is the patch series for ext4 punch hole that I have been working on.
> There is still a little more debugging that I would like to do with it,
> but I've had some requests to see the patch, so I'm sending it out a bit
> early. Any feed back is appreciated. Thx!
Hi Allison,
Very nice work!
One meta comment is related to locking considerations with direct I/O.
I am not all that familiar with all direct I/O paths (i.e. dioread_nolock),
but I smell a possible race with holes initiation via direct I/O.
The thing with direct I/O is that you have no flags to test the state
of the block (did Eric just add a hash table to cope with another issue?).
Direct I/O writes outside i_size are synchronous (i.e. i_mutex is held until
I/O completion), but inside i_size, they may be a-synchronous.
The case of initiating holes is currently handled with DIO_SKIP_HOLES
by falling back to buffered I/O, although it could be handled by allocating
an uninitialized extent.
The case of writing to falloced space in handled by converting extents to
initialized at async I/O completion.
I am not sure there a race with hole punching here and I am not even sure
that the description above is totally accurate (?), but it's a dark corner,
which should to be reviewed carefully.
>
> This first patch adds a function to convert a range of blocks
> to an uninitialized extent. This function will
> be used to first convert the blocks to extents before
> punching them out.
>
> This function also adds a routine to split an extent at
> a given block. This routine is used when a range of
> blocks to be converted is only partially contained in
> an extent.
>
> Signed-off-by: Allison Henderson <achender@...ibm.com>
> ---
> :100644 100644 7516fb9... ab2e42e... M fs/ext4/extents.c
> fs/ext4/extents.c | 185 +++++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 files changed, 185 insertions(+), 0 deletions(-)
>
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index 7516fb9..ab2e42e 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -2169,6 +2169,105 @@ static int ext4_remove_blocks(handle_t *handle, struct inode *inode,
> return 0;
> }
>
> +/*
> + * ext4_split_extents() Splits a given extent at the block "split"
> + * @handle: The journal handle
> + * @inode: The file inode
> + * @split: The block where the extent will be split
> + * @path: The path to the extent
> + * @flags: flags used to insert the new extent
> + */
> +static int ext4_split_extents(handle_t *handle,
> + struct inode *inode,
> + ext4_lblk_t split,
> + struct ext4_ext_path *path,
> + int flags)
> +{
> + struct ext4_extent *ex, newex, orig_ex, *i_ex;
> + struct ext4_extent *ex1 = NULL;
> + struct ext4_extent *ex2 = NULL;
> + struct ext4_extent_header *eh;
> + ext4_lblk_t ee_block;
> + unsigned int ee_len, depth;
> + ext4_fsblk_t newblock, origblock;
> + int err = 0;
> +
> + ext_debug("ext4_split_extent: inode %lu, split %u\n", inode->i_ino, split);
> + ext4_ext_show_leaf(inode, path);
> +
> + depth = ext_depth(inode);
> + eh = path[depth].p_hdr;
> + ex = path[depth].p_ext;
> + ee_block = le32_to_cpu(ex->ee_block);
> + ee_len = ext4_ext_get_actual_len(ex);
> +
> + /* if the block is not actually in the extent, go to out */
> + if(split > ee_block+ee_len || split < ee_block)
> + goto out;
> +
> + origblock = ee_block + ext4_ext_pblock(ex);
> + newblock = split - ee_block + ext4_ext_pblock(ex);
> + ext_debug("The new block is %llu, the orig block is: %llu\n", newblock, origblock);
> +
> + /* save original block in case split fails */
> + orig_ex.ee_block = ex->ee_block;
> + orig_ex.ee_len = cpu_to_le16(ee_len);
> + ext4_ext_store_pblock(&orig_ex, ext4_ext_pblock(ex));
> +
> + err = ext4_ext_get_access(handle, inode, path + depth);
> + if (err)
> + goto out;
> +
> + ex1 = ex;
> + ex1->ee_len = cpu_to_le16(split-ee_block);
> +
> + ex2 = &newex;
> + ex2->ee_len = cpu_to_le16(ee_len-(split-ee_block));
> + ex2->ee_block = split;
> + ext4_ext_store_pblock(ex2, newblock);
> +
> + if (ex1->ee_block != ex2->ee_block)
> + goto insert;
> +
> + /* Mark modified extent as dirty */
> + err = ext4_ext_dirty(handle, inode, path + depth);
> + ext_debug("out here\n");
> + goto out;
> +insert:
> +
> + /*
> + * If this leaf cannot fit in any more extents
> + * insert it into another leaf
> + */
> + if(EXT_LAST_EXTENT(eh) >= EXT_MAX_EXTENT(eh)){
> + err = ext4_ext_insert_extent(handle, inode, path, &newex, flags);
> + if (err)
> + goto fix_extent_len;
> + }
> +
> + /* otherwise just scoot all ther other extents down */
> + else{
> + for(i_ex = EXT_LAST_EXTENT(eh); i_ex > ex1; i_ex-- ){
> + memcpy(i_ex+1, i_ex, sizeof(struct ext4_extent));
> + }
> + memcpy(ex1+1, ex2, sizeof(struct ext4_extent));
> + eh->eh_entries++;
> + }
> +
> +out:
> + ext4_ext_show_leaf(inode, path);
> + return err;
> +
> +fix_extent_len:
> + ex->ee_block = orig_ex.ee_block;
> + ex->ee_len = orig_ex.ee_len;
> + ext4_ext_store_pblock(ex, ext4_ext_pblock(&orig_ex));
> + ext4_ext_mark_uninitialized(ex);
> + ext4_ext_dirty(handle, inode, path + depth);
> +
> + return err;
> +}
> +
> static int
> ext4_ext_rm_leaf(handle_t *handle, struct inode *inode,
> struct ext4_ext_path *path, ext4_lblk_t start)
> @@ -3598,6 +3697,92 @@ out_stop:
> ext4_journal_stop(handle);
> }
>
> +/*
> + * ext4_ext_convert_blocks_uninit()
> + * Converts a range of blocks to uninitialized
> + *
> + * @inode: The files inode
> + * @handle: The journal handle
(style) in all other functions, @handle comes before @inode
I'm sorry, but this hurts my eyes :-)
> + * @lblock: The logical block where the conversion will start
> + * @len: The max number of blocks to convert
> + *
> + * Returns the number of blocks successfully converted
> + */
> +static int ext4_ext_convert_blocks_uninit(struct inode *inode, handle_t *handle, ext4_lblk_t lblock, ext4_lblk_t len){
> +
> + ext4_lblk_t ee_block, iblock;
> + struct ext4_ext_path *path;
> + struct ext4_extent *ex;
> + unsigned int ee_len;
> + int ret, err = 0;
> +
> + iblock = lblock;
> + while(iblock < lblock+len){
> +
> + path = ext4_ext_find_extent(inode, lblock, NULL);
> +
> + if(path == NULL)
> + goto next;
> +
> + err = ext4_ext_get_access(handle, inode, path);
> + if(err < 0)
> + goto next;
> +
> + ex = path->p_ext;
> + if(ex == NULL)
> + goto next;
> +
> + ee_block = le32_to_cpu(ex->ee_block);
> + ee_len = ext4_ext_get_actual_len(ex);
> +
> + /*
> + * If the block is in the middle of the extent,
> + * split the extent to remove the head.
> + * Then find the new extent that contains the block
> + */
> + if(ee_block < iblock){
> + err = ext4_split_extents(handle, inode, iblock, path, 0);
> + if(err)
> + goto next;
> +
> + path = ext4_ext_find_extent(inode, iblock, NULL);
> +
> + if(path == NULL)
> + goto next;
> +
> + ex = path->p_ext;
> + if(ex == NULL)
> + goto next;
> +
> + ee_block = le32_to_cpu(ex->ee_block);
> + ee_len = ext4_ext_get_actual_len(ex);
> +
> + }
> +
> + /* If the extent exceeds len, split the extent to remove the tail */
> + if(ee_len > len){
> + err = ext4_split_extents(handle, inode, lblock+len, path, 0);
> + if(err)
> + goto next;
> +
> + ee_len = ext4_ext_get_actual_len(ex);
> + }
> +
> + /* Mark the extent uninitialized */
> + ext4_ext_mark_uninitialized(ex);
> +
> + iblock+=ex->ee_len;
> + ret+=ex->ee_len;
> + continue;
> +next:
> + /* If the extent for this block cannot be found, skip it */
> + iblock++;
> + }
> +
> + return ret;
> +}
> +
> +
> static void ext4_falloc_update_inode(struct inode *inode,
> int mode, loff_t new_size, int update_ctime)
> {
> --
> 1.7.1
>
>
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