Izik Eidus wrote:
Ksm is driver that allow merging identical pages between one or more
applications in way unvisible to the application that use it.
Pages that are merged are marked as readonly and are COWed when any
application try to change them.
Ksm is used for cases where using fork() is not suitable,
one of this cases is where the pages of the application keep changing
dynamicly and the application cannot know in advance what pages are
going to be identical.
Ksm works by walking over the memory pages of the applications it
scan in order to find identical pages.
It uses a two sorted data strctures called stable and unstable trees
to find in effective way the identical pages.
When ksm finds two identical pages, it marks them as readonly and merges
them into single one page,
after the pages are marked as readonly and merged into one page, linux
will treat this pages as normal copy_on_write pages and will fork them
when write access will happen to them.
Ksm scan just memory areas that were registred to be scanned by it.
Ksm api:
KSM_GET_API_VERSION:
Give the userspace the api version of the module.
KSM_CREATE_SHARED_MEMORY_AREA:
Create shared memory reagion fd, that latter allow the user to register
the memory region to scan by using:
KSM_REGISTER_MEMORY_REGION and KSM_REMOVE_MEMORY_REGION
KSM_START_STOP_KTHREAD:
Return information about the kernel thread, the inforamtion is returned
using the ksm_kthread_info structure:
ksm_kthread_info:
__u32 sleep:
number of microsecoends to sleep between each iteration of
scanning.
__u32 pages_to_scan:
number of pages to scan for each iteration of scanning.
__u32 max_pages_to_merge:
maximum number of pages to merge in each iteration of scanning
(so even if there are still more pages to scan, we stop this
iteration)
__u32 flags:
flags to control ksmd (right now just ksm_control_flags_run
available)
Wouldn't this make more sense as a sysfs interface? That is, the
KSM_START_STOP_KTHREAD part, not necessarily the rest of the API.
Regards,
Anthony Liguori
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