From 026d0d27c4882303e4b071ca6d996640cc2932c3 Mon Sep 17 00:00:00 2001 From: "Kiselev, Oleg" Date: Wed, 20 Jul 2022 04:26:22 +0000 Subject: [PATCH] ext4: reduce computation of overhead during resize This patch avoids doing an O(n**2)-complexity walk through every flex group. Instead, it uses the already computed overhead information for the newly allocated space, and simply adds it to the previously calculated overhead stored in the superblock. This drastically reduces the time taken to resize very large bigalloc filesystems (from 3+ hours for a 64TB fs down to milliseconds). Signed-off-by: Oleg Kiselev Link: https://lore.kernel.org/r/CE4F359F-4779-45E6-B6A9-8D67FDFF5AE2@amazon.com Signed-off-by: Theodore Ts'o --- fs/ext4/resize.c | 23 +++++++++++++++++++++-- 1 file changed, 21 insertions(+), 2 deletions(-) diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c index e4e89ca82f8c..5e3a893e600e 100644 --- a/fs/ext4/resize.c +++ b/fs/ext4/resize.c @@ -1383,6 +1383,17 @@ static int ext4_setup_new_descs(handle_t *handle, struct super_block *sb, return err; } +static void ext4_add_overhead(struct super_block *sb, + const ext4_fsblk_t overhead) +{ + struct ext4_sb_info *sbi = EXT4_SB(sb); + struct ext4_super_block *es = sbi->s_es; + + sbi->s_overhead += overhead; + es->s_overhead_clusters = cpu_to_le32(sbi->s_overhead); + smp_wmb(); +} + /* * ext4_update_super() updates the super block so that the newly added * groups can be seen by the filesystem. @@ -1484,9 +1495,17 @@ static void ext4_update_super(struct super_block *sb, } /* - * Update the fs overhead information + * Update the fs overhead information. + * + * For bigalloc, if the superblock already has a properly calculated + * overhead, update it with a value based on numbers already computed + * above for the newly allocated capacity. */ - ext4_calculate_overhead(sb); + if (ext4_has_feature_bigalloc(sb) && (sbi->s_overhead != 0)) + ext4_add_overhead(sb, + EXT4_NUM_B2C(sbi, blocks_count - free_blocks)); + else + ext4_calculate_overhead(sb); es->s_overhead_clusters = cpu_to_le32(sbi->s_overhead); if (test_opt(sb, DEBUG))