Public bug reported:
We are using kernel version 5.15.0-52-lowlatency. We noticed that the
/proc/meminfo shows the dirty bytes value as below.
# cat /proc/meminfo | grep -i dirty
Dirty: 380024 kB
However we have set the dirty_background_bytes value to writeback at
250M. This background flush is not happening. We do know that we havent
set any time based flushing since we want the kernel to only do the
writebacks based on size. This issue happens sporadically and looks like
the kernel lost track of certain dirty pages. To mitigate this issue if
we set writeback_centisecs value to anything other than 0, kernel comes
in and flushes the pages immediately. So based on this observation it
looks like the kernel lost track of its dirty bytes accounting. Please
let us know how to troubleshoot this issue and fix this.
Dirty values configured:
# sysctl -a | grep -i dirty
vm.dirty_background_bytes = 262144000
vm.dirty_background_ratio = 0
vm.dirty_bytes = 0
vm.dirty_expire_centisecs = 0
vm.dirty_ratio = 10
vm.dirty_writeback_centisecs = 0
vm.dirtytime_expire_seconds = 43200
** Affects: lowlatency-kernel (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/2121549
Title:
Dirty pages not flushed to disk on background threshold
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