Re: [PATCH] ext4: dir inode reservation V3

Mingming Cao
2007-11-20T02:13:53Z

On Tue, 2007-11-13 at 22:12 +0800, Coly Li wrote:
> Basic idea of my dir inode reservation patch can be found here,
> http://lists.openwall.net/linux-ext4/2007/11/05/3
>
> 1, What does dir inode reservation do
> Dir inode reservation tries to reserve several inodes in inodes table for a directory when this
> directory is created. When create new file under this directory, try to allocate inode from the
> reserved inodes area. This is called as dir_ireserve inode allocator.
>
Thanks for the update.

Let me try to understand your method:

So the basic idea is not do linear inode allocation for directory? Inode
structure block for directory file is only coming from block 0, N, N
+N,... where the number of skipped blocks N is stored in the in-core
superblock structure.

When ever need to allocate an inode for directory, skip N reserved bits
(space for N*16 inodes) if the previous block is already allocated. That
way place two directories with the hole of N*16 inodes structures, then
allow files under the first directory stay closer with their parent
directory. Is this correct?

> 4, Dir inode reservation is optional
> Dir inode reservation is optional, you can use -o followed by one of these options to enable dir
> inode reservation during mount ext4 file system:
> dir_ireserve=low
> dir_ireserve=normal
> dir_ireserve=high

Would be nice to pass the tuning info low/normal/high(16/64/128 blocks
correspondingly) via something else rather than mount options.

> Currently, 'low' reserves 15 file inodes for each directory, 'normal' reserves 31 inodes and 'high'
> reserves 127 inodes. Reserving more than 127 inodes does not help to performance obviously.
>
>
> 5, Performance number
> On a Core-Duo, 2MB DDM memory, 7200 RPM SATA PC, I built a 50GB ext4 partition, and tried to create
> 50000 directories, and create 15 (1KB) files in each directory alternatively. After a remount, I
> tried to remove all the directories and files recursively by a 'rm -rf'. Bellow is the benchmark result,
> normal ext4 ext4 with dir inode reservation
> mount options: -o data=writeback -o data=writeback,dir_ireserve=low
> Create dirs: real 0m49.101s real 2m59.703s
> Create files: real 24m17.962s real 21m8.161s
> Unlink all: real 24m43.788s real 17m29.862s
> Creating dirs with dir inode reservation is slower than normal ext4 as predicted, because allocating
> directory inodes in non-linear order will cause extra hard disk seeking and block I/O.

Hmm...I suspect there is bug in your patch, the extra seek should not
contribute to 4 times slower

>
> #include <linux/time.h>
> @@ -478,6 +480,75 @@ static int find_group_other(struct super_block *sb, struct inode *parent,
> return -1;
> }
>
> +static int ext4_ino_from_ireserve(handle_t *handle, struct inode *dir,
> + int mode, ext4_group_t *group, unsigned long *ino)
> +{
> + struct super_block *sb;
> + struct ext4_sb_info *sbi;
> + struct ext4_group_desc *gdp = NULL;
> + struct buffer_head *gdp_bh = NULL, *bitmap_bh = NULL;
> + ext4_group_t ires_group = *group;
> + unsigned long ires_ino;
> + int i, bit;
> +
> + sb = dir->i_sb;
> + sbi = EXT4_SB(sb);
> +
> + /* if the inode number is not for directory,
> + * only try to allocate after directory's inode
> + */
> + if (!S_ISDIR(mode)) {
> + *ino = dir->i_ino % EXT4_INODES_PER_GROUP(sb);
> + return 0;
> + }
> +
> + /* reserve inodes for new directory */
> + for (i = 0; i < sbi->s_groups_count; i++) {
> + gdp = ext4_get_group_desc(sb, ires_group, &gdp_bh);
> + if (!gdp)
> + goto fail;
> + bit = 0;
> +try_same_group:
> + if (bit < EXT4_INODES_PER_GROUP(sb)) {
> + brelse(bitmap_bh);
> + bitmap_bh = read_inode_bitmap(sb, ires_group);
> + if (!bitmap_bh)
> + goto fail;
> +
> + BUFFER_TRACE(bitmap_bh, "get_write_access");
> + if (ext4_journal_get_write_access(
> + handle, bitmap_bh) != 0)
> + goto fail;
> + if (!ext4_set_bit_atomic(sb_bgl_lock(sbi, ires_group),
> + bit, bitmap_bh->b_data)) {
> + /* we won it */
> + BUFFER_TRACE(bitmap_bh,
> + "call ext4_journal_dirty_metadata");
> + if (ext4_journal_dirty_metadata(handle,
> + bitmap_bh) != 0)
> + goto fail;
> + ires_ino = bit;
> + goto find;
> + }
> + /* we lost it */
> + jbd2_journal_release_buffer(handle, bitmap_bh);
> + bit += sbi->s_dir_ireserve_nr;
> + goto try_same_group;
> + }
> + if (++ires_group == sbi->s_groups_count)
> + ires_group = 0;
> + }
> + goto fail;
> +find:
> + brelse(bitmap_bh);
> + *group = ires_group;
> + *ino = ires_ino;
> + return 0;
> +fail:
> + brelse(bitmap_bh);
> + return -ENOSPC;
> +}
> +
> /*
> * There are two policies for allocating an inode. If the new inode is
> * a directory, then a forward search is made for a block group with both
> @@ -543,6 +614,12 @@ struct inode *ext4_new_inode(handle_t *handle, struct inode * dir, int mode)
>
> ino = 0;
>
> + if (test_opt(sb, DIR_IRESERVE)) {
> + err = ext4_ino_from_ireserve(handle, dir,
> + mode, &group, &ino);
> + if ((!err) && S_ISDIR(mode))
> + goto got;
> + }

So you are calling ext4_ino_from_ireserve() inside a loop iterate all
block groups? I think this is bug, it should move outside of the loop.

> repeat_in_this_group:
> ino = ext4_find_next_zero_bit((unsigned long *)
> bitmap_bh->b_data, EXT4_INODES_PER_GROUP(sb), ino);
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index b626339..9b873b7 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -884,6 +884,7 @@ enum {
> Opt_commit, Opt_journal_update, Opt_journal_inum, Opt_journal_dev,
> Opt_journal_checksum, Opt_journal_async_commit,
> Opt_abort, Opt_data_journal, Opt_data_ordered, Opt_data_writeback,
> + Opt_dir_ireserve_low, Opt_dir_ireserve_normal, Opt_dir_ireserve_high,
> Opt_usrjquota, Opt_grpjquota, Opt_offusrjquota, Opt_offgrpjquota,
> Opt_jqfmt_vfsold, Opt_jqfmt_vfsv0, Opt_quota, Opt_noquota,
> Opt_ignore, Opt_barrier, Opt_err, Opt_resize, Opt_usrquota,
> @@ -929,6 +930,9 @@ static match_table_t tokens = {
> {Opt_data_journal, "data=journal"},
> {Opt_data_ordered, "data=ordered"},
> {Opt_data_writeback, "data=writeback"},
> + {Opt_dir_ireserve_low, "dir_ireserve=low"},
> + {Opt_dir_ireserve_normal, "dir_ireserve=normal"},
> + {Opt_dir_ireserve_high, "dir_ireserve=high"},
> {Opt_offusrjquota, "usrjquota="},
> {Opt_usrjquota, "usrjquota=%s"},
> {Opt_offgrpjquota, "grpjquota="},
> @@ -1311,6 +1315,18 @@ clear_qf_name:
> return 0;
> sbi->s_stripe = option;
> break;
> + case Opt_dir_ireserve_low:
> + set_opt(sbi->s_mount_opt, DIR_IRESERVE);
> + sbi->s_dir_ireserve_nr = EXT4_DIR_IRESERVE_LOW;
> + break;
> + case Opt_dir_ireserve_normal:
> + set_opt(sbi->s_mount_opt, DIR_IRESERVE);
> + sbi->s_dir_ireserve_nr = EXT4_DIR_IRESERVE_NORMAL;
> + break;
> + case Opt_dir_ireserve_high:
> + set_opt(sbi->s_mount_opt, DIR_IRESERVE);
> + sbi->s_dir_ireserve_nr = EXT4_DIR_IRESERVE_HIGH;
> + break;
> default:
> printk (KERN_ERR
> "EXT4-fs: Unrecognized mount option \"%s\" "
> diff --git a/include/linux/ext4_fs.h b/include/linux/ext4_fs.h
> index bcdb59d..88f5173 100644
> --- a/include/linux/ext4_fs.h
> +++ b/include/linux/ext4_fs.h
> @@ -92,6 +92,13 @@ struct ext4_allocation_request {
> #define EXT4_GOOD_OLD_FIRST_INO 11
>
> /*
> + * Macro-instructions used to reserve inodes for directories
> + */
> +#define EXT4_DIR_IRESERVE_LOW 16
> +#define EXT4_DIR_IRESERVE_NORMAL 64
> +#define EXT4_DIR_IRESERVE_HIGH 128
> +
> +/*
> * Maximal count of links to a file
> */
> #define EXT4_LINK_MAX 65000
> @@ -502,6 +509,7 @@ do { \
> #define EXT4_MOUNT_JOURNAL_ASYNC_COMMIT 0x1000000 /* Journal Async Commit */
> #define EXT4_MOUNT_DELALLOC 0x2000000 /* Delalloc support */
> #define EXT4_MOUNT_MBALLOC 0x4000000 /* Buddy allocation support */
> +#define EXT4_MOUNT_DIR_IRESERVE 0x10000000/* dir inode reservation */
> /* Compatibility, for having both ext2_fs.h and ext4_fs.h included at once */
> #ifndef _LINUX_EXT2_FS_H
> #define clear_opt(o, opt) o &= ~EXT4_MOUNT_##opt
> diff --git a/include/linux/ext4_fs_sb.h b/include/linux/ext4_fs_sb.h
> index 744e746..790b0cf 100644
> --- a/include/linux/ext4_fs_sb.h
> +++ b/include/linux/ext4_fs_sb.h
> @@ -147,6 +147,8 @@ struct ext4_sb_info {
>
> /* locality groups */
> struct ext4_locality_group *s_locality_groups;
> + /* number of inodes we reserve in a directory */
> + int s_dir_ireserve_nr;
> };
> #define EXT4_GROUP_INFO(sb, group) \
> EXT4_SB(sb)->s_group_info[(group) >> EXT4_DESC_PER_BLOCK_BITS(sb)] \
>
>