On Tuesday 2023-05-23 06:35, Andrei Borzenkov wrote:
Date: Tue, 23 May 2023 06:35:45 From: Andrei Borzenkov <arvidjaar@gmail.com> To: users@lists.opensuse.org Subject: Re: "background idle" syncing of filesystems
On 23.05.2023 07:02, Paul Neuwirth via openSUSE Users wrote:
and I could recreate the issue, after 6 days uptime with high I/O.
from /proc/vmstat: nr_dirty 571064
That is about 22GiB (4K pages)
nr_dirty_threshold 24894434 nr_dirty_background_threshold 12432019
from top: MiB Mem : 515896.2+total, 6047.250 free, 15834.02+used, 501647.4+buff/cache
and finally: # date; sync; date Tue May 23 05:49:06 AM CEST 2023 Tue May 23 05:59:44 AM CEST 2023
-> syncing took > 10 minutes.
This is appr. 32MiB/s. Assuming small random IO (which is also duplicated due to mirroring) I would not call it something extraordinary with two SATA disks. If this data is on btrfs, you have additional metadata which adds to IO randomness (and the amount of metadata could be quite large as well).
So it is quite normal for your workload. The only way to mitigate it is to lower thresholds to force syncing of dirty pages earlier.
What you observe is the typical buffer bloat. If you let data to accumulate you need to wait for data to drain.
thanks for figuring this out. As part of my original post, would lowering /proc/sys/vm/dirty_background_bytes or /proc/sys/vm/dirty_background_ratio affect system performance noticeably? Paul Neuwirth