Hi Stefan! On Tue 06-09-22 22:38:10, Stefan Wahren wrote: > Am 06.09.22 um 17:29 schrieb Jan Kara: > > Hello, > > > > Here is a second version of my mballoc improvements to avoid spreading > > allocations with mb_optimize_scan=1. The patches fix the performance > > regression I was able to reproduce with reaim on my test machine: > > > > mb_optimize_scan=0 mb_optimize_scan=1 patched > > Hmean disk-1 2076.12 ( 0.00%) 2099.37 ( 1.12%) 2032.52 ( -2.10%) > > Hmean disk-41 92481.20 ( 0.00%) 83787.47 * -9.40%* 90308.37 ( -2.35%) > > Hmean disk-81 155073.39 ( 0.00%) 135527.05 * -12.60%* 154285.71 ( -0.51%) > > Hmean disk-121 185109.64 ( 0.00%) 166284.93 * -10.17%* 185298.62 ( 0.10%) > > Hmean disk-161 229890.53 ( 0.00%) 207563.39 * -9.71%* 232883.32 * 1.30%* > > Hmean disk-201 223333.33 ( 0.00%) 203235.59 * -9.00%* 221446.93 ( -0.84%) > > Hmean disk-241 235735.25 ( 0.00%) 217705.51 * -7.65%* 239483.27 * 1.59%* > > Hmean disk-281 266772.15 ( 0.00%) 241132.72 * -9.61%* 263108.62 ( -1.37%) > > Hmean disk-321 265435.50 ( 0.00%) 245412.84 * -7.54%* 267277.27 ( 0.69%) > > > > The changes also significanly reduce spreading of allocations for small / > > moderately sized files. I'm not able to measure a performance difference > > resulting from this but on eMMC storage this seems to be the main culprit > > of reduced performance. Untarring of raspberry-pi archive touches following > > numbers of groups: > > > > mb_optimize_scan=0 mb_optimize_scan=1 patched > > groups 4 22 7 > > > > To achieve this I have added two more changes on top of v1 - patches 4 and 5. > > Patch 4 makes sure we use locality group preallocation even for files that are > > not likely to grow anymore (previously we have disabled all preallocations for > > such files, however locality group preallocation still makes a lot of sense for > > such files). This patch reduced spread of a small file allocations but larger > > file allocations were still spread significantly because they avoid locality > > group preallocation and as they are not power-of-two in size, they also > > immediately start with cr=1 scan. To address that I've changed the data > > structure for looking up the best block group to allocate from (see patch 5 > > for details). > > > > Stefan, can you please test whether these patches fix the problem for you as > > well? Comments & review welcome. > > this looks amazing \o/ > > With this patch v2 applied the untar with mb_optimize_scan=1 is now faster > than mb_optimize_scan=0. > > mb_optimize_scan=0 -> almost 5 minutes > > mb_optimize_scan=1 -> almost 1 minute > > The original scenario (firmware download) with mb_optimize_scan=1 is now > fast as mb_optimize_scan=0. Glad to hear that! > Here the iostat as usual: > > https://github.com/lategoodbye/mb_optimize_scan_regress/commit/f4ad188e0feee60bffa23a8e1ad254544768c3bd > > There is just one thing, but not sure this if this comes from these patches. > If i call > > cat /proc/fs/ext4/mmcblk1p2/mb_structs_summary > > The kernel throw a NULL pointer derefence in > ext4_mb_seq_structs_summary_show Yeah, likely a bug in my last patch. I didn't test my changes to the sysfs interface. Thanks for testing this, I'll have a look. Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
