From mboxrd@z Thu Jan 1 00:00:00 1970 From: Theodore Ts'o Subject: [PATCH 6/6 -v2] e2fsck: optimize pass 5 for CPU utilization Date: Mon, 26 Nov 2012 11:39:40 -0500 Message-ID: <1353947981-15219-7-git-send-email-tytso@mit.edu> References: <1353947981-15219-1-git-send-email-tytso@mit.edu> Cc: Theodore Ts'o To: Ext4 Developers List Return-path: Received: from li9-11.members.linode.com ([67.18.176.11]:34893 "EHLO imap.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755184Ab2KZQp4 (ORCPT ); Mon, 26 Nov 2012 11:45:56 -0500 In-Reply-To: <1353947981-15219-1-git-send-email-tytso@mit.edu> Sender: linux-ext4-owner@vger.kernel.org List-ID: Add a fast past 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 8312fe0..5aff55c 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) -- 1.7.12.rc0.22.gcdd159b