From 53e3120c18c0cb88bc757a7800872a6ca794f163 Mon Sep 17 00:00:00 2001 From: Theodore Ts'o Date: Sat, 24 Nov 2012 19:17:44 -0500 Subject: [PATCH] e2fsck: optimize pass 5 for CPU utilization Add a fast path optimization in e2fsck's pass 5 for the common case where the block bitmap is correct. The optimization works by extracting each block group's block allocation bitmap into a memory buffer, and comparing it with the expected allocation bitmap using memcmp(). If it matches, then we can just update the free block counts and be on our way, and skip checking each bit individually. Addresses-Google-Bug: #7534813 Signed-off-by: "Theodore Ts'o" Reviewed-by: Lukas Czerner --- e2fsck/pass5.c | 55 ++++++++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 53 insertions(+), 2 deletions(-) diff --git a/e2fsck/pass5.c b/e2fsck/pass5.c index 8312fe0d..5aff55cb 100644 --- a/e2fsck/pass5.c +++ b/e2fsck/pass5.c @@ -212,6 +212,12 @@ static void check_block_bitmaps(e2fsck_t ctx) int cmp_block = 0; int redo_flag = 0; blk64_t super_blk, old_desc_blk, new_desc_blk; + char *actual_buf, *bitmap_buf; + + actual_buf = (char *) e2fsck_allocate_memory(ctx, fs->blocksize, + "actual bitmap buffer"); + bitmap_buf = (char *) e2fsck_allocate_memory(ctx, fs->blocksize, + "bitmap block buffer"); clear_problem_context(&pctx); free_array = (unsigned int *) e2fsck_allocate_memory(ctx, @@ -259,11 +265,53 @@ redo_counts: for (i = B2C(fs->super->s_first_data_block); i < ext2fs_blocks_count(fs->super); i += EXT2FS_CLUSTER_RATIO(fs)) { + int first_block_in_bg = (B2C(i) - + B2C(fs->super->s_first_data_block)) % + fs->super->s_clusters_per_group == 0; + int n, nbytes = fs->super->s_clusters_per_group / 8; + actual = ext2fs_fast_test_block_bitmap2(ctx->block_found_map, i); + /* + * Try to optimize pass5 by extracting a bitmap block + * as expected from what we have on disk, and then + * comparing the two. If they are identical, then + * update the free block counts and go on to the next + * block group. This is much faster than doing the + * individual bit-by-bit comparison. The one downside + * is that this doesn't work if we are asking e2fsck + * to do a discard operation. + */ + if (!first_block_in_bg || + (group == (int)fs->group_desc_count - 1) || + (ctx->options & E2F_OPT_DISCARD)) + goto no_optimize; + + retval = ext2fs_get_block_bitmap_range2(ctx->block_found_map, + B2C(i), fs->super->s_clusters_per_group, + actual_buf); + if (retval) + goto no_optimize; + if (ext2fs_bg_flags_test(fs, group, EXT2_BG_BLOCK_UNINIT)) + memset(bitmap_buf, 0, nbytes); + else { + retval = ext2fs_get_block_bitmap_range2(fs->block_map, + B2C(i), fs->super->s_clusters_per_group, + bitmap_buf); + if (retval) + goto no_optimize; + } + if (memcmp(actual_buf, bitmap_buf, nbytes) != 0) + goto no_optimize; + n = ext2fs_bitcount(actual_buf, nbytes); + group_free = fs->super->s_clusters_per_group - n; + free_blocks += group_free; + i += fs->super->s_clusters_per_group - 1; + goto next_group; + no_optimize: + if (skip_group) { - if ((B2C(i) - B2C(fs->super->s_first_data_block)) % - fs->super->s_clusters_per_group == 0) { + if (first_block_in_bg) { super_blk = 0; old_desc_blk = 0; new_desc_blk = 0; @@ -401,6 +449,7 @@ redo_counts: if (!bitmap && i >= first_free) e2fsck_discard_blocks(ctx, first_free, (i - first_free) + 1); + next_group: first_free = ext2fs_blocks_count(fs->super); free_array[group] = group_free; @@ -475,6 +524,8 @@ redo_counts: } errout: ext2fs_free_mem(&free_array); + ext2fs_free_mem(&actual_buf); + ext2fs_free_mem(&bitmap_buf); } static void check_inode_bitmaps(e2fsck_t ctx)