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fat: optimize fat_count_free_clusters()

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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 <hirofumi@mail.parknet.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
OGAWA Hirofumi 2008-01-08 15:32:41 -08:00 committed by Linus Torvalds
parent d52df2e2ea
commit 9f966be899
1 changed files with 28 additions and 0 deletions
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28
fs/fat/fatent.c
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@ -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;