Re: KSM Algorithm

[Izik Eidus <izik@qumranet.com>]

ציטוט Sukanto Ghosh:
> Can anyone answer these queries regarding KSM ?
>
> How does KSM offers its services through the  /dev/ksm device ?
>   
ioctls

> 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...)

> 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

> 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

> 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

> --
> Regards,
> Sukanto Ghosh
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