Hey Marcus,
The first thing I would try is:
https://www.kernel.org/doc/Documentation/sysctl/vm.txt
It's the basic docs that describes the function by itself and it's
technical idea.
Once you know the function idea you might understand a bit more about
why to choose one value over the other.
For example "vm.swapiness" as "0" is nice but there is a reason that the
swap actually happen.
The main issue with it is that there was a usage for above a specific
amount of memory on the system.
You would feel the "slow" speed of the service and then understand that
it is using more swap that it needs and understand that the service
works utilizing lots of ram which the system was designed to not use always.
A really good design should results in a system that is not utilizing
100% of it's RAM by default.
When the ram is used by 100% and you need to check your options you
cannot even consider running a simple "ls" since this will cause the
system to get stuck if the DISK has high I/O rate.
You can say that all the defaults are kind of designed to let the system
to stay stable enough to allow Start it UP.
On cases you do know the size of the system I would tune them if I
understand the meaning of them to prevent real damage and to first allow
me breath some air before diving into any decision regarding a big system.
All The Bests,
Eliezer
On 03/12/13 13:04, Marcus Bointon wrote:
On 3 Dec 2013, at 06:13, Robert Hajime Lanning <lanning@xxxxxxxxxx> wrote:
I have these tuned for my system:
vm.swappiness
vm.vfs_cache_pressure
vm.dirty_background_ratio
vm.dirty_ratio
vm.dirty_writeback_centisecs
vm.dirty_expire_centisecs
This pretty much goes for any storage server that is filesystem based (ext2/3/4,xfs,btrfs,zfs...)
Very important to tune these values when you have large amounts of RAM.
Do you happen to have any good guides on tuning those? I've only encountered swappiness before.
Marcus
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