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

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Date:	Thu, 02 Apr 2009 16:32:20 +0300
From:	Izik Eidus <ieidus@...hat.com>
To:	Chris Wright <chrisw@...hat.com>
CC:	Anthony Liguori <anthony@...emonkey.ws>,
	Andrea Arcangeli <aarcange@...hat.com>,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	linux-mm@...ck.org, avi@...hat.com, riel@...hat.com,
	jeremy@...p.org, mtosatti@...hat.com, hugh@...itas.com,
	corbet@....net, yaniv@...hat.com, dmonakhov@...nvz.org
Subject: Re: [PATCH 5/4] update ksm userspace interfaces

Chris Wright wrote:
> * Anthony Liguori (anthony@...emonkey.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?
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