Re: [PATCH] ext4: dir inode reservation V3

[Mingming Cao]

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)] \
> 
> 

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