From 020d7721d9de525e511b4778795d375675160844 Mon Sep 17 00:00:00 2001
From: Sami Liedes <sami.liedes@xxxxxx>
Date: Sat, 10 Mar 2012 22:50:51 +0200
Subject: [PATCH] libext2fs: Implement fast find_first_zero() for bitarray
bitmaps.
With this change the CPU time needed to shrink a 100G filesystem drops
to 0.8% of the original (17 CPU seconds instead of 2057).
Signed-off-by: Sami Liedes <sami.liedes@xxxxxx>
diff --git a/lib/ext2fs/blkmap64_ba.c b/lib/ext2fs/blkmap64_ba.c
index 3f0c643..8eddde9 100644
--- a/lib/ext2fs/blkmap64_ba.c
+++ b/lib/ext2fs/blkmap64_ba.c
@@ -317,6 +317,86 @@ static void ba_print_stats(ext2fs_generic_bitmap bitmap)
sizeof(struct ext2fs_ba_private_struct));
}
+/* Find the first zero bit between start and end, inclusive. */
+static errcode_t ba_find_first_zero(ext2fs_generic_bitmap bitmap,
+ __u64 start, __u64 end, __u64 *out)
+{
+ ext2fs_ba_private bp = (ext2fs_ba_private)bitmap->private;
+ unsigned long bitpos = start - bitmap->start;
+ unsigned long count = end - start + 1;
+ int byte_found = 0; /* whether a != 0xff byte has been found */
+ const unsigned char *pos;
+ unsigned long max_loop_count, i;
+
+ if (start < bitmap->start || end > bitmap->end || start > end)
+ return EINVAL;
+
+ if (bitmap->cluster_bits)
+ return EINVAL;
+
+ /* scan bits until we hit a byte boundary */
+ while ((bitpos & 0x7) != 0 && count > 0) {
+ if (!ext2fs_test_bit64(bitpos, bp->bitarray)) {
+ *out = bitpos + bitmap->start;
+ return 0;
+ }
+ bitpos++;
+ count--;
+ }
+
+ if (!count)
+ return ENOENT;
+
+ pos = ((unsigned char *)bp->bitarray) + (bitpos >> 3);
+ /* scan bytes until 8-byte (64-bit) aligned */
+ while (count >= 8 && (((unsigned long)pos) & 0x07)) {
+ if (*pos != 0xff) {
+ byte_found = 1;
+ break;
+ }
+ pos++;
+ count -= 8;
+ bitpos += 8;
+ }
+
+ if (!byte_found) {
+ max_loop_count = count >> 6; /* 8-byte blocks */
+ i = max_loop_count;
+ while (i) {
+ if (*((const __u64 *)pos) != ((__u64)-1))
+ break;
+ pos += 8;
+ i--;
+ }
+ count -= 64 * (max_loop_count - i);
+ bitpos += 64 * (max_loop_count - i);
+
+ max_loop_count = count >> 3;
+ i = max_loop_count;
+ while (i) {
+ if (*pos != 0xff) {
+ byte_found = 1;
+ break;
+ }
+ pos++;
+ i--;
+ }
+ count -= 8 * (max_loop_count - i);
+ bitpos += 8 * (max_loop_count - i);
+ }
+
+ /* Here either count < 8 or byte_found == 1. */
+ while (count-- > 0) {
+ if (!ext2fs_test_bit64(bitpos, bp->bitarray)) {
+ *out = bitpos + bitmap->start;
+ return 0;
+ }
+ bitpos++;
+ }
+
+ return ENOENT;
+}
+
struct ext2_bitmap_ops ext2fs_blkmap64_bitarray = {
.type = EXT2FS_BMAP64_BITARRAY,
.new_bmap = ba_new_bmap,
@@ -333,4 +413,5 @@ struct ext2_bitmap_ops ext2fs_blkmap64_bitarray = {
.get_bmap_range = ba_get_bmap_range,
.clear_bmap = ba_clear_bmap,
.print_stats = ba_print_stats,
+ .find_first_zero = ba_find_first_zero
};
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