ציטוט Sukanto Ghosh:
Are every guest pages scanned in KVM while using KSM or page-scanning
and sharing is triggered on some event (low memory, etc) ?
no, the scanning run all the time (with number pages to scan and sleep
parameters...)
Does the scanner(s) run as separate kernel threads ?\
it can run as kernel thread / or by ioctl runing from userspace
Is sharing done only between the pages which have been registered via
KSM_REGISTER_MEMORY_REGION ?
yes
What are these for ? KSM_CREATE_SHARED_MEMORY_AREA and KSM_CREATE_SCAN ?
KSM_CREATE_SHARED_MEMORY_AREA - to register memory area to be scanned for
identical pages
KSM_CREATE_SCAN - to create the scanner that scan for this pages
So kvm will create a scanner using KSM_CREATE_SCAN ioctl to /dev/ksm.
kvm sets its parameters which specify the frequency of scan operation.
Then, it tries to determine periodically from the shadow page tables
about the guest memory region, and registers them with the /dev/ksm.
The scanner as configured will scan the registered areas and will
create COW shared pages for identical pages.
Am I right ?
yea
Doesn't KSM notifies KVM about the shared pages so that KVM can update
its sptes accordingly or is it done by KSM itself ?
when using kvm, mmu notifiers is a must for ksm, (mmu notifiers update
kvm about the changes in the host page table)
What about KSM being used by someone other than KVM ? Does KSM updates
the ptes of the shared pages itself ?
it can be used by any application, it update the ptes of the host, what
you mean by the shared pages itself?
Where are the shared pages kept ? In kernel memory ? Aren't the shared
pages always pinned in RAM (due to same reasons for pinned shadowed
pages) ?
in the version that was sent to the list it was kernel memory (meaning
shared pages are not swappable
(just the pages that are shared not the pages that we scan, when they are
split beacuse of copy on write it become swappable again
new version that i will send soon the pages are normal anonymous/userspace
memory that is swappable
What is the strategy/method which you will use to represent the shared
memory as normal anonymous/userspace memory ? Then, these pages must
be staying at one of the guest's address-space (whose pages have been
shared) ?
it possible due to another patch that i need to send, that allow modules
register new reverse mapping call backs...,
How much is the overhead involved due to this ?
depeand on the speed you tell it to scan, but the overhead is about ~5% for
common cases
Can I know the typical values of the parameters : sleep time, no. of
pages to scan, which you used to arrive at the above mentioned
overhead.
i think it is about 256 2000 (256 pages per 2000 usleep)
(note that most of the cpu is acutlay taken by the copying of the pages
when a new shared page is created, i have possible way to change it and
reduce the cpu even more
but i dont know if i want to do it) (it add more IFs to the fast path
inside the mm)
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to [EMAIL PROTECTED]
More majordomo info at http://vger.kernel.org/majordomo-info.html
