Mine aren't missing a 0, I divided wrong and added a 0, so I am using
5MB and 3MB, which would leave my spread at 2MB or at say 100MB/sec
1/50sec. It has been a long time since I set them and my system works
decent during copying.
On Tue, Mar 31, 2020 at 7:22 PM Samuel Sieb <samuel(a)sieb.net> wrote:
>
> 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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