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Commit 9f966be8 authored by OGAWA Hirofumi's avatar OGAWA Hirofumi Committed by Linus Torvalds
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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: default avatarOGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent d52df2e2

fs/fat/fatent.c

+28 −0
Original line number Diff line number Diff line
@@ -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);

}



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;