exfat: using ffs instead of internal logic

Replaced the internal table lookup algorithm with ffs of
the bitops library with better performance.

Use it to increase the single processing length of the
exfat_find_free_bitmap function, from single-byte search to long type.

Signed-off-by: John Sanpe <sanpeqf@gmail.com>
Acked-by: Sungjong Seo <sj1557.seo@samsung.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>

2 files changed, 16 insertions, 28 deletions

diff --git a/fs/exfat/balloc.c b/fs/exfat/balloc.c
index 3e3e9e4cce2f..0356c88252bd 100644
--- a/fs/exfat/balloc.c
+++ b/fs/exfat/balloc.c
@@ -14,29 +14,15 @@
 #if BITS_PER_LONG == 32
 #define __le_long __le32
 #define lel_to_cpu(A) le32_to_cpu(A)
+#define cpu_to_lel(A) cpu_to_le32(A)
 #elif BITS_PER_LONG == 64
 #define __le_long __le64
 #define lel_to_cpu(A) le64_to_cpu(A)
+#define cpu_to_lel(A) cpu_to_le64(A)
 #else
 #error "BITS_PER_LONG not 32 or 64"
 #endif
 
-static const unsigned char free_bit[] = {
-	0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0, 4, 0, 1, 0, 2,/*  0 ~  19*/
-	0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0, 5, 0, 1, 0, 2, 0, 1, 0, 3,/* 20 ~  39*/
-	0, 1, 0, 2, 0, 1, 0, 4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2,/* 40 ~  59*/
-	0, 1, 0, 6, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0, 4,/* 60 ~  79*/
-	0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0, 5, 0, 1, 0, 2,/* 80 ~  99*/
-	0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0, 4, 0, 1, 0, 2, 0, 1, 0, 3,/*100 ~ 119*/
-	0, 1, 0, 2, 0, 1, 0, 7, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2,/*120 ~ 139*/
-	0, 1, 0, 4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0, 5,/*140 ~ 159*/
-	0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0, 4, 0, 1, 0, 2,/*160 ~ 179*/
-	0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0, 6, 0, 1, 0, 2, 0, 1, 0, 3,/*180 ~ 199*/
-	0, 1, 0, 2, 0, 1, 0, 4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2,/*200 ~ 219*/
-	0, 1, 0, 5, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0, 4,/*220 ~ 239*/
-	0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0                /*240 ~ 254*/
-};
-
 /*
  *  Allocation Bitmap Management Functions
  */
@@ -195,32 +181,35 @@ unsigned int exfat_find_free_bitmap(struct super_block *sb, unsigned int clu)
 {
 	unsigned int i, map_i, map_b, ent_idx;
 	unsigned int clu_base, clu_free;
-	unsigned char k, clu_mask;
+	unsigned long clu_bits, clu_mask;
 	struct exfat_sb_info *sbi = EXFAT_SB(sb);
+	__le_long bitval;
 
 	WARN_ON(clu < EXFAT_FIRST_CLUSTER);
-	ent_idx = CLUSTER_TO_BITMAP_ENT(clu);
-	clu_base = BITMAP_ENT_TO_CLUSTER(ent_idx & ~(BITS_PER_BYTE_MASK));
+	ent_idx = ALIGN_DOWN(CLUSTER_TO_BITMAP_ENT(clu), BITS_PER_LONG);
+	clu_base = BITMAP_ENT_TO_CLUSTER(ent_idx);
 	clu_mask = IGNORED_BITS_REMAINED(clu, clu_base);
 
 	map_i = BITMAP_OFFSET_SECTOR_INDEX(sb, ent_idx);
 	map_b = BITMAP_OFFSET_BYTE_IN_SECTOR(sb, ent_idx);
 
 	for (i = EXFAT_FIRST_CLUSTER; i < sbi->num_clusters;
-	     i += BITS_PER_BYTE) {
-		k = *(sbi->vol_amap[map_i]->b_data + map_b);
+	     i += BITS_PER_LONG) {
+		bitval = *(__le_long *)(sbi->vol_amap[map_i]->b_data + map_b);
 		if (clu_mask > 0) {
-			k |= clu_mask;
+			bitval |= cpu_to_lel(clu_mask);
 			clu_mask = 0;
 		}
-		if (k < 0xFF) {
-			clu_free = clu_base + free_bit[k];
+		if (lel_to_cpu(bitval) != ULONG_MAX) {
+			clu_bits = lel_to_cpu(bitval);
+			clu_free = clu_base + ffz(clu_bits);
 			if (clu_free < sbi->num_clusters)
 				return clu_free;
 		}
-		clu_base += BITS_PER_BYTE;
+		clu_base += BITS_PER_LONG;
+		map_b += sizeof(long);
 
-		if (++map_b >= sb->s_blocksize ||
+		if (map_b >= sb->s_blocksize ||
 		    clu_base >= sbi->num_clusters) {
 			if (++map_i >= sbi->map_sectors) {
 				clu_base = EXFAT_FIRST_CLUSTER;
diff --git a/fs/exfat/exfat_fs.h b/fs/exfat/exfat_fs.h
index a7a2c35d74fb..8030780a199b 100644
--- a/fs/exfat/exfat_fs.h
+++ b/fs/exfat/exfat_fs.h
@@ -135,8 +135,7 @@ enum {
 #define BITMAP_OFFSET_BIT_IN_SECTOR(sb, ent) (ent & BITS_PER_SECTOR_MASK(sb))
 #define BITMAP_OFFSET_BYTE_IN_SECTOR(sb, ent) \
 	((ent / BITS_PER_BYTE) & ((sb)->s_blocksize - 1))
-#define BITS_PER_BYTE_MASK	0x7
-#define IGNORED_BITS_REMAINED(clu, clu_base) ((1 << ((clu) - (clu_base))) - 1)
+#define IGNORED_BITS_REMAINED(clu, clu_base) ((1UL << ((clu) - (clu_base))) - 1)
 
 #define ES_ENTRY_NUM(name_len)	(ES_IDX_LAST_FILENAME(name_len) + 1)
 /* 19 entries = 1 file entry + 1 stream entry + 17 filename entries */