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Message-Id: <949C18DE-F36E-4D7E-897A-FFC5865EF79C@dilger.ca>
Date: Tue, 29 Jan 2019 18:58:46 -0700
From: Andreas Dilger <adilger@...ger.ca>
To: harshadshirwadkar@...il.com
Cc: umka@...udlinux.com, linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext4: shrink directory when last block is empty
On Jan 23, 2019, at 11:32 AM, harshadshirwadkar@...il.com wrote:
>
> From: Harshad Shirwadkar <harshadshirwadkar@...il.com>
>
> This patch is the first step towards shrinking htree based directories
> when files are deleted. We truncate directory inode when a directory
> entry removal causes last directory block to be empty. This patch just
> removes the last block. We may end up in a situation where many
> intermediate dirent blocks in directory inode are empty. Removing
> those blocks would be handled later.
>
> Signed-off-by: Harshad Shirwadkar <harshadshirwadkar@...il.com>
> ---
> fs/ext4/namei.c | 130 ++++++++++++++++++++++++++++++++++++++++--------
> 1 file changed, 109 insertions(+), 21 deletions(-)
>
> diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
> index 2a4c25c4681d..79cb88ba898a 100644
> --- a/fs/ext4/namei.c
> +++ b/fs/ext4/namei.c
> @@ -273,7 +273,8 @@ static int ext4_htree_next_block(struct inode *dir, __u32 hash,
> __u32 *start_hash);
> static struct buffer_head * ext4_dx_find_entry(struct inode *dir,
> struct ext4_filename *fname,
> - struct ext4_dir_entry_2 **res_dir);
> + struct ext4_dir_entry_2 **res_dir,
> + struct dx_frame *dx_frame);
(style) these should align after '(' on the first line
> @@ -380,6 +381,7 @@ static void ext4_dirent_csum_set(struct inode *inode,
> (void *)t - (void *)dirent);
> }
>
> +
> int ext4_handle_dirty_dirent_node(handle_t *handle,
> struct inode *inode,
> struct buffer_head *bh)
(style) No need for this hunk.
> @@ -866,6 +868,42 @@ dx_probe(struct ext4_filename *fname, struct inode *dir,
> return ret_err;
> }
>
> +static void
> +ext4_dx_delete_entry(handle_t *handle, struct inode *dir,
> + struct dx_frame *dx_frame, __le64 block)
> +{
> + struct dx_entry *entries;
> + unsigned int count, limit;
> + int err, i;
> +
> + entries = dx_frame->entries;
> + count = dx_get_count(entries);
> + limit = dx_get_limit(entries);
> +
> + for (i = 0; i < count; i++)
> + if (entries[i].block == block)
> + break;
> +
> + if (i >= count)
> + return;
> +
> + err = ext4_journal_get_write_access(handle, dx_frame->bh);
> + if (err) {
> + ext4_std_error(dir->i_sb, err);
> + return;
> + }
> +
> + for (; i < count - 1; i++)
> + entries[i] = entries[i + 1];
> +
> + dx_set_count(entries, count - 1);
> + dx_set_limit(entries, limit);
I don't think you need to update the limit just because of the count changing?
This is just setting it back to the same value that dx_get_limit() returned earlier.
> @@ -1309,6 +1347,14 @@
> +static int is_empty_dirent_block(struct inode *dir, struct buffer_head *bh)
(style) this function should be type bool. The older "is_*" functions were written
before "bool" was available in the kernel, though a separate cleanup patch to convert
them to bool would be welcome.
> +{
> + struct ext4_dir_entry_2 *de = (struct ext4_dir_entry_2 *)bh->b_data;
> +
> + return (ext4_rec_len_from_disk(de->rec_len, dir->i_sb->s_blocksize)
> + == dir->i_sb->s_blocksize);
(style) no need for () around return value.
>
> @@ -1339,7 +1385,8 @@ static int is_dx_internal_node(struct inode *dir, ext4_lblk_t block,
> static struct buffer_head * ext4_find_entry (struct inode *dir,
> const struct qstr *d_name,
> struct ext4_dir_entry_2 **res_dir,
> - int *inlined)
> + int *inlined,
> + struct dx_frame *dx_frame)
(style) this can fit on the previous line, and they can all align after '(' on
the first line. Please also remove the space after '*' in the function declaration.
> @@ -1486,9 +1533,10 @@ static struct buffer_head * ext4_find_entry (struct inode *dir,
> return ret;
> }
>
> -static struct buffer_head * ext4_dx_find_entry(struct inode *dir,
> - struct ext4_filename *fname,
> - struct ext4_dir_entry_2 **res_dir)
> +static struct buffer_head *ext4_dx_find_entry(
> + struct inode *dir, struct ext4_filename *fname,
(style) it isn't clear why you moved "struct inode *dir" from the previous line?
The continued lines look like they can properly align after '(' on the previous line.
> @@ -2337,9 +2389,13 @@ int ext4_generic_delete_entry(handle_t *handle,
> static int ext4_delete_entry(handle_t *handle,
> struct inode *dir,
> struct ext4_dir_entry_2 *de_del,
> - struct buffer_head *bh)
> + struct buffer_head *bh,
> + struct dx_frame *dx_frame)
> {
> + struct ext4_map_blocks map;
> int err, csum_size = 0;
> + int should_truncate = 0;
(style) bool should_truncate
> @@ -2363,11 +2419,35 @@ static int ext4_delete_entry(handle_t *handle,
> if (err)
> goto out;
>
> + if (dx_frame && dx_frame->bh && is_empty_dirent_block(dir, bh)) {
> +
(style) no blank line here.
> + map.m_lblk = (dir->i_size - 1) >>
> + (dir->i_sb->s_blocksize_bits);
(style) no need for parenthesis around dir->i_sb->s_blocksize_bits.
(style) this can fit on the previous line and still be under 80 columns.
> + map.m_len = 1;
> + err = ext4_map_blocks(handle, dir, &map, 0);
> +
> + if ((err > 0) && (bh->b_blocknr == map.m_pblk)) {
(style) no need for extra parenthesis around "err > 0" and "b_blocknr == m_pblk".
> + ext4_dx_delete_entry(handle, dir, dx_frame,
> + cpu_to_le64(map.m_lblk));
> + should_truncate = 1;
> + }
> + }
> +
> BUFFER_TRACE(bh, "call ext4_handle_dirty_metadata");
> +
> err = ext4_handle_dirty_dirent_node(handle, dir, bh);
> if (unlikely(err))
> goto out;
>
> + if (should_truncate) {
> + dir->i_size -= dir->i_sb->s_blocksize;
> + ext4_truncate(dir);
Since we have already mapped the last block above, I wonder if we can do something
lighter weight than calling ext4_truncate() here? Maybe moving the ext4_truncate()
guts into a helper function like ext4_truncate_internal() that avoids all of the
complexity (orphan list, resizing the transaction, inline data, etc).
> + if (dir->i_size == dir->i_sb->s_blocksize) {
> + ext4_clear_inode_flag(dir, EXT4_INODE_INDEX);
> + ext4_mark_inode_dirty(handle, dir);
Are there any places in the code that assume an indexed directory will remain as such?
The tricky part here is that any valid htree directory will have 3 blocks (dx_root,
plus two leaf blocks), so it might be problematic to go back to a single non-htree
block, especially since this doesn't look like it has any locking. It is probably
worthwhile to check the code for this.
> @@ -2985,6 +3065,9 @@ static int ext4_unlink(struct inode *dir, struct dentry *dentry)
> struct buffer_head *bh;
> struct ext4_dir_entry_2 *de;
> handle_t *handle = NULL;
> + struct dx_frame dx_frame;
> +
> + memset(&dx_frame, 0, sizeof(dx_frame));
Rather than an explicit memset(), this can use a struct initializer when it is declared:
struct dx_frame dx_frame = { NULL };
Are there existing xfstests that cover this case? Certainly deleting files from a
directory, but it would be useful to have something that checks whether the directory
size is shrinking and this code is working.
Cheers, Andreas
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