From: Baokun Li <libaokun1@huawei.com> mainline inclusion from mainline-v6.17-rc1 commit e9eec6f33971fbfcdd32fd1c7dd515ff4d2954c0 category: feature bugzilla: https://gitee.com/openeuler/kernel/issues/ICN2MB Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i... -------------------------------- When ext4 allocates blocks, we used to just go through the block groups one by one to find a good one. But when there are tons of block groups (like hundreds of thousands or even millions) and not many have free space (meaning they're mostly full), it takes a really long time to check them all, and performance gets bad. So, we added the "mb_optimize_scan" mount option (which is on by default now). It keeps track of some group lists, so when we need a free block, we can just grab a likely group from the right list. This saves time and makes block allocation much faster. But when multiple processes or containers are doing similar things, like constantly allocating 8k blocks, they all try to use the same block group in the same list. Even just two processes doing this can cut the IOPS in half. For example, one container might do 300,000 IOPS, but if you run two at the same time, the total is only 150,000. Since we can already look at block groups in a non-linear way, the first and last groups in the same list are basically the same for finding a block right now. Therefore, add an ext4_try_lock_group() helper function to skip the current group when it is locked by another process, thereby avoiding contention with other processes. This helps ext4 make better use of having multiple block groups. Also, to make sure we don't skip all the groups that have free space when allocating blocks, we won't try to skip busy groups anymore when ac_criteria is CR_ANY_FREE. Performance test data follows: Test: Running will-it-scale/fallocate2 on CPU-bound containers. Observation: Average fallocate operations per container per second. |CPU: Kunpeng 920 | P80 | |Memory: 512GB |-------------------------| |960GB SSD (0.5GB/s)| base | patched | |-------------------|-------|-----------------| |mb_optimize_scan=0 | 2667 | 4821 (+80.7%) | |mb_optimize_scan=1 | 2643 | 4784 (+81.0%) | |CPU: AMD 9654 * 2 | P96 | |Memory: 1536GB |-------------------------| |960GB SSD (1GB/s) | base | patched | |-------------------|-------|-----------------| |mb_optimize_scan=0 | 3450 | 15371 (+345%) | |mb_optimize_scan=1 | 3209 | 6101 (+90.0%) | Signed-off-by: Baokun Li <libaokun1@huawei.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Ojaswin Mujoo <ojaswin@linux.ibm.com> Reviewed-by: Zhang Yi <yi.zhang@huawei.com> Link: https://patch.msgid.link/20250714130327.1830534-2-libaokun1@huawei.com Signed-off-by: Theodore Ts'o <tytso@mit.edu> Conflicts: fs/ext4/mballoc.c [Because of already merged-in hulk commit da6eb19e6550 ("ext4: add ext4_try_lock_group() to skip busy groups").] Signed-off-by: Baokun Li <libaokun1@huawei.com> --- fs/ext4/mballoc.c | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-) diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c index ec2808247f4f..d7a1fcbdcff6 100644 --- a/fs/ext4/mballoc.c +++ b/fs/ext4/mballoc.c @@ -899,8 +899,8 @@ static void ext4_mb_choose_next_group_p2_aligned(struct ext4_allocation_context bb_largest_free_order_node) { if (sbi->s_mb_stats) atomic64_inc(&sbi->s_bal_cX_groups_considered[CR_POWER2_ALIGNED]); - if (likely(ext4_mb_good_group(ac, iter->bb_group, CR_POWER2_ALIGNED)) && - !spin_is_locked(ext4_group_lock_ptr(ac->ac_sb, iter->bb_group))) { + if (!spin_is_locked(ext4_group_lock_ptr(ac->ac_sb, iter->bb_group)) && + likely(ext4_mb_good_group(ac, iter->bb_group, CR_POWER2_ALIGNED))) { *group = iter->bb_group; ac->ac_flags |= EXT4_MB_CR_POWER2_ALIGNED_OPTIMIZED; read_unlock(&sbi->s_mb_largest_free_orders_locks[i]); @@ -936,8 +936,8 @@ ext4_mb_find_good_group_avg_frag_lists(struct ext4_allocation_context *ac, int o list_for_each_entry(iter, frag_list, bb_avg_fragment_size_node) { if (sbi->s_mb_stats) atomic64_inc(&sbi->s_bal_cX_groups_considered[cr]); - if (likely(ext4_mb_good_group(ac, iter->bb_group, cr)) && - !spin_is_locked(ext4_group_lock_ptr(ac->ac_sb, iter->bb_group))) { + if (!spin_is_locked(ext4_group_lock_ptr(ac->ac_sb, iter->bb_group)) && + likely(ext4_mb_good_group(ac, iter->bb_group, cr))) { grp = iter; break; } @@ -2899,6 +2899,11 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac) nr, &prefetch_ios); } + /* prevent unnecessary buddy loading. */ + if (cr < CR_ANY_FREE && + spin_is_locked(ext4_group_lock_ptr(sb, group))) + continue; + /* This now checks without needing the buddy page */ ret = ext4_mb_good_group_nolock(ac, group, cr); if (ret <= 0) { -- 2.39.2