From 9f966be8996f2829406324c68e4c67c2d64d864b Mon Sep 17 00:00:00 2001 From: OGAWA Hirofumi Date: Tue, 8 Jan 2008 15:32:41 -0800 Subject: [PATCH] fat: optimize fat_count_free_clusters() 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: root@devron (/)# time df -h > /dev/null real 0m1.202s user 0m0.000s sys 0m0.440s with patch: root@devron (/)# time df -h > /dev/null real 0m0.378s user 0m0.012s sys 0m0.168s Signed-off-by: OGAWA Hirofumi Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/fat/fatent.c | 28 ++++++++++++++++++++++++++++ 1 file changed, 28 insertions(+) diff --git a/fs/fat/fatent.c b/fs/fat/fatent.c index 2c1b73fb82ae..5fb366992b73 100644 --- a/fs/fat/fatent.c +++ b/fs/fat/fatent.c @@ -590,21 +590,49 @@ int fat_free_clusters(struct inode *inode, int cluster) 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); +} + int fat_count_free_clusters(struct super_block *sb) { struct msdos_sb_info *sbi = MSDOS_SB(sb); struct fatent_operations *ops = sbi->fatent_ops; struct fat_entry fatent; + unsigned long reada_blocks, reada_mask, cur_block; int err = 0, free; lock_fat(sbi); if (sbi->free_clusters != -1) goto out; + reada_blocks = FAT_READA_SIZE >> sb->s_blocksize_bits; + reada_mask = reada_blocks - 1; + cur_block = 0; + free = 0; fatent_init(&fatent); fatent_set_entry(&fatent, FAT_START_ENT); while (fatent.entry < sbi->max_cluster) { + /* readahead of fat blocks */ + if ((cur_block & reada_mask) == 0) { + unsigned long rest = sbi->fat_length - cur_block; + fat_ent_reada(sb, &fatent, min(reada_blocks, rest)); + } + cur_block++; + err = fat_ent_read_block(sb, &fatent); if (err) goto out;