[PATCH 5.17 0136/1126] ext4: make mb_optimize_scan performance mount option work with extents

Greg Kroah-Hartman
2022-04-05T07:46:48Z

From: Ojaswin Mujoo <ojaswin@linux.ibm.com>

commit 077d0c2c78df6f7260cdd015a991327efa44d8ad upstream.

Currently mb_optimize_scan scan feature which improves filesystem
performance heavily (when FS is fragmented), seems to be not working
with files with extents (ext4 by default has files with extents).

This patch fixes that and makes mb_optimize_scan feature work
for files with extents.

Below are some performance numbers obtained when allocating a 10M and 100M
file with and w/o this patch on a filesytem with no 1M contiguous block.

<perf numbers>
===============
Workload: dd if=/dev/urandom of=test conv=fsync bs=1M count=10/100

Time taken
=====================================================
no. Size without-patch with-patch Diff(%)
1 10M 0m8.401s 0m5.623s 33.06%
2 100M 1m40.465s 1m14.737s 25.6%

<debug stats>
=============
w/o patch:
mballoc:
reqs: 17056
success: 11407
groups_scanned: 13643
cr0_stats:
hits: 37
groups_considered: 9472
useless_loops: 36
bad_suggestions: 0
cr1_stats:
hits: 11418
groups_considered: 908560
useless_loops: 1894
bad_suggestions: 0
cr2_stats:
hits: 1873
groups_considered: 6913
useless_loops: 21
cr3_stats:
hits: 21
groups_considered: 5040
useless_loops: 21
extents_scanned: 417364
goal_hits: 3707
2^n_hits: 37
breaks: 1873
lost: 0
buddies_generated: 239/240
buddies_time_used: 651080
preallocated: 705
discarded: 478

with patch:
mballoc:
reqs: 12768
success: 11305
groups_scanned: 12768
cr0_stats:
hits: 1
groups_considered: 18
useless_loops: 0
bad_suggestions: 0
cr1_stats:
hits: 5829
groups_considered: 50626
useless_loops: 0
bad_suggestions: 0
cr2_stats:
hits: 6938
groups_considered: 580363
useless_loops: 0
cr3_stats:
hits: 0
groups_considered: 0
useless_loops: 0
extents_scanned: 309059
goal_hits: 0
2^n_hits: 1
breaks: 1463
lost: 0
buddies_generated: 239/240
buddies_time_used: 791392
preallocated: 673
discarded: 446

Fixes: 196e402 (ext4: improve cr 0 / cr 1 group scanning)
Cc: stable@kernel.org
Reported-by: Geetika Moolchandani <Geetika.Moolchandani1@ibm.com>
Reported-by: Nageswara R Sastry <rnsastry@linux.ibm.com>
Suggested-by: Ritesh Harjani <riteshh@linux.ibm.com>
Signed-off-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Link: https://lore.kernel.org/r/fc9a48f7f8dcfc83891a8b21f6dd8cdf056ed810.1646732698.git.ojaswin@linux.ibm.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/ext4/mballoc.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -1000,7 +1000,7 @@ static inline int should_optimize_scan(s
return 0;
if (ac->ac_criteria >= 2)
return 0;
- if (ext4_test_inode_flag(ac->ac_inode, EXT4_INODE_EXTENTS))
+ if (!ext4_test_inode_flag(ac->ac_inode, EXT4_INODE_EXTENTS))
return 0;
return 1;
}