On 05.11.2014 21:07, Adam Litke wrote:
On 04/11/14 13:11 +0100, Sven Kieske wrote:
Hi,
currently ksmd is a single process and is thus bound to one core.
This leads to some scaling problems such as:
If you got a lot of vms on one host with huge amounts of ram you can observe that the cpu usage by ksmd goes easily to 100%. I wonder what would be the benefit here... I think spending CPU cycles on something like memory compression is not what (most) users would do. Already I think this is an annoyance; maybe thats why the process is niced to +5. A multi process daemon would require careful confining (with cgroups). To my understanding the for KSM to really work well is to have many (idle / high mem) guests which are quite similar?
I wonder if ksmd could not be split up in child/worker threads, thus enabling higher density of vms on one host.
It's likely going to be trickier than you imagine with the added locking that would be required to synchronize the ksmd threads. Actually I was refraining to answer Svens question since I lack some knowledge here. But I guessed synchronization was the reason for the single threadted design. Some serous work needs to be done on KSM do achieve this goal. I was thinking about some map/reduce aglo to do that... OTOH mangeling with mem pages of guests very requires special care.
or can this just be tweaked by altering values in /etc/ksmtuned.conf ?
I don't think it can.
What do you think?
Interesting idea.
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