On 21/03/2017 22:16, Kai Krakow wrote:
Test one by one... Either disable all, then enable one by one, or
vice-versa.
Chances are that your FS may be blocking on sync. Do you maybe have a
very high value in /proc/sys/vm/dirty_background_{ratio,bytes}?
If ratio is 0, then bytes is used. Ratio is a percent of your physical
RAM. With the default kernel value in modern systems, this is
ridiculously high for desktop systems. Maybe put a fixed value, like
128MB. The dirty background value is the amount of outstanding writes
before a foreground process blocks on further writes. If this value is
high, a sync may cause processes to freeze for a long time. Setting
this to a lower value forces single processes to block early and give
the kernel a chance to write back dirty data.
The next value to check is dirty_{ratio,bytes}. That is the combined
maximum of outstanding data before the cache must be flushed. If this
is hit, all writing processes freeze. So, having the background value
high gives a greater chance of hitting this early.
The default values are 10% and 20% (ratio). I've made the 20% ratio
into 10% and put 128MB for background which works quite well:
Foreground processes are blocked for shorter times (because writing
128MB can be a few seconds or less, where 1.6GB can be minutes in a
worse case, so if overall limit is hit, I'm screwed). The overall
dirty buffer is still big enough to let the system buffer writes of
multiple processes. My system has 16GB RAM, you may want to adjust it
or try different values.
$ cat /etc/sysctl.d/98-caching.conf
vm.dirty_background_bytes = 134217728
vm.dirty_ratio = 10
Maybe point your Firefox cache to a tmpfs. If you're using tmpfs, don't
put swappiness to low, otherwise data sitting in tmpfs cannot be
swapped out and will cause filesystem caches to be discarded to early.
I'm working with a 32GB tmpfs and standard swappiness for emerge, and I
see no problems although multiple gigabytes of emerge build data may be
swapped out. Still, emerge is so much faster now. But then, my swaps
are on different disks (and I have multiple for getting some RAID-like
striping of swap space).
Also, depending on which FS you're using, trying deadline instead of
CFQ may greatly improve your desktop experience (browsers should
benefit most from this).
You may be onto something here:
This is an 8-core i7 latop, 16G RAM
$ sudo cat /proc/sys/vm/dirty_background_bytes
0
$ sudo cat /proc/sys/vm/dirty_background_ratio
5
$ sudo cat /proc/sys/vm/dirty_bytes
0
$ sudo cat /proc/sys/vm/dirty_ratio
10
browser cache is on a regular laptop spinning-rust 500G disk
IO scheduler is BFQ, I use it for ages now.
I did tests some years back and found it overall the best for an
interactive desktop with a DE. I haven't repeated those tests since, has
there been significant changes in this are last year or three?
--
Alan McKinnon
alan.mckin...@gmail.com
