linux-ext4 - Re: [PATCH] ext4 statfs speed up

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Date:	Fri, 06 Jul 2007 02:44:03 +0800
From:	coly li <colyli@...il.com>
To:	Badari Pulavarty <pbadari@...ibm.com>
Cc:	ext4 <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH] ext4 statfs speed up

Badari,

How about the performance improvement, is there any benchmark result ?

Coly


在 2007-07-05四的 11:11 -0700，Badari Pulavarty写道：
> This is a patch that speeds up statfs.  It is very simple - 
> the "overhead" calculation, which takes a huge amount of time 
> for large filesystems, never changes unless the size of the 
> filesystem itself changes.  That means we can store it in memory 
> and only recalculate if the filesystem has been resized (almost 
> never).
> 
> It also fixes a minor problem that we never update the on-disk 
> superblock free blocks/inodes counts until the filesystem is 
> unmounted.  While not fatal, we may as well update that on disk 
> when we have the information, and it makes things like debugfs 
> and dumpe2fs report a bit more accurate info.
> 
> Signed-off-by: Badari Pulavarty <pbadari@...ibm.com>
> Signed-off-by: Andreas Dilger <adilger@...sterfs.com>
> 
>  fs/ext4/super.c            |   25 +++++++++++++++----------
>  include/linux/ext4_fs_sb.h |    2 ++
>  2 files changed, 17 insertions(+), 10 deletions(-)
> 
> Index: linux-2.6.22-rc7/include/linux/ext4_fs_sb.h
> ===================================================================
> --- linux-2.6.22-rc7.orig/include/linux/ext4_fs_sb.h	2007-07-01 12:54:24.000000000 -0700
> +++ linux-2.6.22-rc7/include/linux/ext4_fs_sb.h	2007-07-04 22:09:59.000000000 -0700
> @@ -39,6 +39,8 @@ struct ext4_sb_info {
>  	unsigned long s_gdb_count;	/* Number of group descriptor blocks */
>  	unsigned long s_desc_per_block;	/* Number of group descriptors per block */
>  	unsigned long s_groups_count;	/* Number of groups in the fs */
> +	unsigned long s_overhead_last;  /* Last calculated overhead */
> +	unsigned long s_blocks_last;    /* Last seen block count */
>  	struct buffer_head * s_sbh;	/* Buffer containing the super block */
>  	struct ext4_super_block * s_es;	/* Pointer to the super block in the buffer */
>  	struct buffer_head ** s_group_desc;
> Index: linux-2.6.22-rc7/fs/ext4/super.c
> ===================================================================
> --- linux-2.6.22-rc7.orig/fs/ext4/super.c	2007-07-01 12:54:24.000000000 -0700
> +++ linux-2.6.22-rc7/fs/ext4/super.c	2007-07-04 22:12:27.000000000 -0700
> @@ -2481,19 +2481,19 @@ static int ext4_statfs (struct dentry * 
>  	struct super_block *sb = dentry->d_sb;
>  	struct ext4_sb_info *sbi = EXT4_SB(sb);
>  	struct ext4_super_block *es = sbi->s_es;
> -	ext4_fsblk_t overhead;
> -	int i;
>  	u64 fsid;
>  
> -	if (test_opt (sb, MINIX_DF))
> -		overhead = 0;
> -	else {
> -		unsigned long ngroups;
> -		ngroups = EXT4_SB(sb)->s_groups_count;
> +	if (test_opt(sb, MINIX_DF)) {
> +		sbi->s_overhead_last = 0;
> +	} else if (sbi->s_blocks_last != le32_to_cpu(es->s_blocks_count)) {
> +		unsigned long ngroups = sbi->s_groups_count, i;
> +		ext4_fsblk_t overhead = 0;
>  		smp_rmb();
>  
>  		/*
> -		 * Compute the overhead (FS structures)
> +		 * Compute the overhead (FS structures).  This is constant
> +		 * for a given filesystem unless the number of block groups
> +		 * changes so we cache the previous value until it does.
>  		 */
>  
>  		/*
> @@ -2517,18 +2517,23 @@ static int ext4_statfs (struct dentry * 
>  		 * Every block group has an inode bitmap, a block
>  		 * bitmap, and an inode table.
>  		 */
> -		overhead += (ngroups * (2 + EXT4_SB(sb)->s_itb_per_group));
> +		overhead += ngroups * (2 + sbi->s_itb_per_group);
> +		sbi->s_overhead_last = overhead;
> +		smp_wmb();
> +		sbi->s_blocks_last = le32_to_cpu(es->s_blocks_count);
>  	}
>  
>  	buf->f_type = EXT4_SUPER_MAGIC;
>  	buf->f_bsize = sb->s_blocksize;
> -	buf->f_blocks = ext4_blocks_count(es) - overhead;
> +	buf->f_blocks = ext4_blocks_count(es) - sbi->s_overhead_last;
>  	buf->f_bfree = percpu_counter_sum(&sbi->s_freeblocks_counter);
> +	es->s_free_blocks_count = cpu_to_le32(buf->f_bfree);
>  	buf->f_bavail = buf->f_bfree - ext4_r_blocks_count(es);
>  	if (buf->f_bfree < ext4_r_blocks_count(es))
>  		buf->f_bavail = 0;
>  	buf->f_files = le32_to_cpu(es->s_inodes_count);
>  	buf->f_ffree = percpu_counter_sum(&sbi->s_freeinodes_counter);
> +	es->s_free_inodes_count = cpu_to_le32(buf->f_ffree);
>  	buf->f_namelen = EXT4_NAME_LEN;
>  	fsid = le64_to_cpup((void *)es->s_uuid) ^
>  	       le64_to_cpup((void *)es->s_uuid + sizeof(u64));
> 
> 
> -
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