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ext4: Don't avoid using BLOCK_UNINIT block groups in mballoc
By avoiding the use of not-yet-used block groups (i.e., block groups with the BLOCK_UNINIT flag), mballoc had a tendency to create large files with large non-contiguous gaps. In addition avoiding the use of new block groups had a tendency to push regular file data into the first block group in a flex_bg group, which slows down the speed of e2fsck pass 2, since it has a tendency to seek much more. For example: Before Patch After Patch Time in seconds Time in seconds Real / User/ Sys MB/s Real / User/ Sys MB/s Pass 1 8.52 / 2.21 / 0.46 20.43 8.84 / 4.97 / 1.11 19.68 Pass 2 21.16 / 1.02 / 1.86 11.30 6.54 / 1.77 / 1.78 36.39 Pass 3 0.01 / 0.00 / 0.00 139.00 0.01 / 0.01 / 0.00 128.90 Pass 4 0.16 / 0.15 / 0.00 0.00 0.17 / 0.17 / 0.00 0.00 Pass 5 2.52 / 1.99 / 0.09 0.79 2.31 / 1.78 / 0.06 0.86 Total 32.40 / 5.11 / 2.49 12.81 17.99 / 8.75 / 2.98 23.01 This was on a sample 80 gig root filesystem which was approximately 50% full. Note the improved e2fsck pass 2 performance, by over a factor of 3, due to a decreased number of seeks. (The total amount of I/O in pass 2 was unchanged; the layout of the directory blocks was simply much better from e2fsck's's perspective.) Other changes as a result of this patch on this sample filesystem: Before Patch After Patch # of non-contig files 762 779 # of non-contig directories 571 570 # of BLOCK_UNINIT bg's 307 293 # of INODE_UNINIT bg's 503 503 Out of 640 block groups, of which 333 were in use, this patch caused an extra 14 block groups to be utilized. The number of non-contiguous files did go up slightly, but when measured against the 99.9% of the files (603,154) which were contiguously allocated, this is pretty insignificant. Signed-off-by: "Theodore Ts'o" <tytso@mit.edu> Signed-off-by: Andreas Dilger <adilger@sun.com>
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1 changed files with 1 additions and 8 deletions
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@ -1728,7 +1728,6 @@ static int ext4_mb_good_group(struct ext4_allocation_context *ac,
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unsigned free, fragments;
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unsigned i, bits;
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int flex_size = ext4_flex_bg_size(EXT4_SB(ac->ac_sb));
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struct ext4_group_desc *desc;
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struct ext4_group_info *grp = ext4_get_group_info(ac->ac_sb, group);
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BUG_ON(cr < 0 || cr >= 4);
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@ -1744,10 +1743,6 @@ static int ext4_mb_good_group(struct ext4_allocation_context *ac,
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switch (cr) {
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case 0:
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BUG_ON(ac->ac_2order == 0);
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/* If this group is uninitialized, skip it initially */
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desc = ext4_get_group_desc(ac->ac_sb, group, NULL);
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if (desc->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT))
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return 0;
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/* Avoid using the first bg of a flexgroup for data files */
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if ((ac->ac_flags & EXT4_MB_HINT_DATA) &&
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@ -2067,9 +2062,7 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
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ac->ac_groups_scanned++;
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desc = ext4_get_group_desc(sb, group, NULL);
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if (cr == 0 || (desc->bg_flags &
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cpu_to_le16(EXT4_BG_BLOCK_UNINIT) &&
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ac->ac_2order != 0))
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if (cr == 0)
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ext4_mb_simple_scan_group(ac, &e4b);
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else if (cr == 1 &&
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ac->ac_g_ex.fe_len == sbi->s_stripe)
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