linux-kernel - Re: [PATCH 3/6] ksm: change the KSM_REMOVE_MEMORY

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Date:	Wed, 06 May 2009 19:58:21 +0300
From:	Izik Eidus <ieidus@...hat.com>
To:	Hugh Dickins <hugh@...itas.com>
CC:	Rik van Riel <riel@...hat.com>, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, aarcange@...hat.com,
	chrisw@...hat.com, alan@...rguk.ukuu.org.uk, device@...ana.org,
	linux-mm@...ck.org, nickpiggin@...oo.com.au
Subject: Re: [PATCH 3/6] ksm: change the KSM_REMOVE_MEMORY_REGION ioctl.

Hugh Dickins wrote:
> On Wed, 6 May 2009, Izik Eidus wrote:
>   
>> We can first start with this ioctl interface, later when we add swapping to
>> the pages, we can have madvice, and still (probably easily) support the ioctls
>> by just calling from inside ksm the madvice functions for that specific
>> address)
>>
>> I want to see ksm use madvice, but i believe it require some more changes to
>> mm/*.c, so it probably better to start with merging it when it doesnt touch
>> alot of stuff outisde ksm.c, and then to add swapping and after that add
>> madvice support (when the pages are swappable, everyone can use it)
>>
>> What you think about that?
>>     
>
> I think it's the wrong order to follow.
>
> The /dev/ksm interface is fine for your use while it's out of tree,
> but we want to get the user interface right when bringing it into
> mainline.  I recall Chris being very clear on that too.
>
> Changing from /dev/ksm to madvise() is not a lot of work, it's mainly
> a matter of deleting code, and tidying up interfaces which would need
> more work anyway (I haven't commented on your curious -EPERMs yet!).
>
> It doesn't involve whether you've enabled swapping or not - let's
> forget the CAP_IPC_LOCK idea, and delegate that issue to limitation
> via sysfs, along with the ability to limit wild overuse of the feature
> - permissions on a sysfs node or something else?
>
> It does nudge towards making some decisions which need to be made
> anyway - that tends to be what a correct interface forces upon you.
> Like the issue of whether to go on covering unmapped areas or not -
> though possibly we could put off that decision, if it's doc'ed
> for now.
>
> And if it only covers mapped areas, then there will need to be a
> VM_flag for it, mainly so mm can call into ksm.c when it's unmapped;
> but I don't see it sinking hooks deeply into mm/*.c.
>
> Hugh
>   
Ok, i give up, lets move to madvice(), i will write a patch that move 
the whole thing into madvice after i finish here something, but that 
ofcurse only if Andrea agree for the move?
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