On Mon, 05 Nov 2007 07:09:00 +0900
OGAWA Hirofumi <[EMAIL PROTECTED]> wrote:
> On large partition, scanning the free clusters is very slow if users
> doesn't use "usefree" option.
>
> For optimizing it, this patch uses sb_breadahead() to read of FAT
> sectors. On some user's 15GB partition, this patch improved it very
> much (1min => 600ms).
>
> The following is the result of 2GB partition on my machine.
>
> without patch:
> [EMAIL PROTECTED] (/)# time df -h > /dev/null
>
> real 0m1.202s
> user 0m0.000s
> sys 0m0.440s
>
> with patch:
> [EMAIL PROTECTED] (/)# time df -h > /dev/null
>
> real 0m0.378s
> user 0m0.012s
> sys 0m0.168s
>
Can't complain about that ;)
> ---
>
> fs/fat/fatent.c | 28 ++++++++++++++++++++++++++++
> 1 file changed, 28 insertions(+)
>
> diff -puN fs/fat/fatent.c~fat_optimize-count-freeclus fs/fat/fatent.c
> --- linux-2.6/fs/fat/fatent.c~fat_optimize-count-freeclus 2007-11-05
> 06:01:10.000000000 +0900
> +++ linux-2.6-hirofumi/fs/fat/fatent.c 2007-11-05 06:01:10.000000000
> +0900
> @@ -590,21 +590,49 @@ error:
>
> EXPORT_SYMBOL_GPL(fat_free_clusters);
>
> +/* 128kb is the whole sectors for FAT12 and FAT16 */
> +#define FAT_READA_SIZE (128 * 1024)
> +
> +static void fat_ent_reada(struct super_block *sb, struct fat_entry *fatent,
> + unsigned long reada_blocks)
> +{
> + struct fatent_operations *ops = MSDOS_SB(sb)->fatent_ops;
> + sector_t blocknr;
> + int i, offset;
> +
> + ops->ent_blocknr(sb, fatent->entry, &offset, &blocknr);
> +
> + for (i = 0; i < reada_blocks; i++)
> + sb_breadahead(sb, blocknr + i);
> +}
You might find that it's simpler and faster to call
page_cache_sync_readahead() against sb->s_bdev->bd_inode->i_mapping.
Or maybe not - that requires a struct file_ra_state. We _used_ to have a
nice simple read-some-stuff-into-pagecache function which didn't need an
ra_state but that seems to have disappeared in the various recent readahead
churn. Oh well.
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