On 3/31/20 5:00 PM, Roger Heflin wrote:
These are what I set:
vm.dirty_background_bytes = 3000000
vm.dirty_bytes = 5000000
I think you're missing a zero. If those are your actual numbers, you
have a very small buffer. Even with your numbers that seems a little small.
I have noticed that copy big files especially over USB bogs the system
pretty badly. I'll try modifying my settings to see if it helps.
That limits the to-be-written bytes to 50Mb, and when it hits 50MB it
will clear the write cache down to 30MB and let writes happen again.
Since 20MB of writes happens pretty fast on modern HD's this makes
response reasonable. If these 2 values are 0 then these 2 rule:
vm.dirty_background_ratio = 0
vm.dirty_ratio = 0
You can only set one or the other. Setting the bytes resets the ratio
and vice versa.
You might note what the default is, all my system have it overridden.
/proc/sys/vm/dirty_background_ratio: 10
/proc/sys/vm/dirty_ratio: 20
Here's the info on those settings from the kernel doc:
https://www.kernel.org/doc/Documentation/sysctl/vm.txt
==============================================================
dirty_background_bytes
Contains the amount of dirty memory at which the background kernel
flusher threads will start writeback.
Note: dirty_background_bytes is the counterpart of
dirty_background_ratio. Only
one of them may be specified at a time. When one sysctl is written it is
immediately taken into account to evaluate the dirty memory limits and the
other appears as 0 when read.
==============================================================
dirty_background_ratio
Contains, as a percentage of total available memory that contains free pages
and reclaimable pages, the number of pages at which the background kernel
flusher threads will start writing out dirty data.
The total available memory is not equal to total system memory.
==============================================================
dirty_bytes
Contains the amount of dirty memory at which a process generating disk
writes
will itself start writeback.
Note: dirty_bytes is the counterpart of dirty_ratio. Only one of them may be
specified at a time. When one sysctl is written it is immediately taken into
account to evaluate the dirty memory limits and the other appears as 0 when
read.
Note: the minimum value allowed for dirty_bytes is two pages (in bytes); any
value lower than this limit will be ignored and the old configuration
will be
retained.
==============================================================
dirty_ratio
Contains, as a percentage of total available memory that contains free pages
and reclaimable pages, the number of pages at which a process which is
generating disk writes will itself start writing out dirty data.
The total available memory is not equal to total system memory.
==============================================================
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