Re: [PATCH 5/4] update ksm userspace interfaces

Izik Eidus
2009-04-02T13:37:30Z

Chris Wright wrote:
> * Anthony Liguori (anthony@codemonkey.ws) wrote:
>
>> Using an interface like madvise() would force the issue to be dealt with
>> properly from the start :-)
>>
>
> Yeah, I'm not at all opposed to it.
>
> This updates to madvise for register and sysfs for control.
>
> madvise issues:
> - MADV_SHAREABLE
> - register only ATM, can add MADV_UNSHAREABLE to allow an app to proactively
> unregister, but need a cleanup when ->mm goes away via exit/exec
> - will register a region per vma, should probably push the whole thing
> into vma rather than keep [mm,addr,len] tuple in ksm
>
>
The main problem that ksm will face when removing the fd interface is:
right now when you register memory into ksm, you open fd, and then ksm
do get_task_mm(), we will do mmput when the file will be closed
(note that this doesnt mean that if you fork and not close the fd the
memory wont go away...., get_task_mm() doesnt protect the vmas inside
the mm strcture and therefore they will be able to get removed)

So if we move into madvice and we remove the get_task_mm() usage, we
will have to add notification to exit_mm() so ksm will know it should
stop using this mm strcture, and drop it from all the trees data...

Is this what we want?