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

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Message-ID: <20090506161424.GC15712@x200.localdomain>
Date:	Wed, 6 May 2009 09:14:24 -0700
From:	Chris Wright <chrisw@...hat.com>
To:	Izik Eidus <ieidus@...hat.com>
Cc:	Hugh Dickins <hugh@...itas.com>, 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.

* Izik Eidus (ieidus@...hat.com) wrote:
> But why not go go step by step?
> 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)

Then we have 2 interfaces to maintain.  Makes more sense to try and get
it right the first time.

> 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)

There's already locking issues w/ using madvise and ksm, so yes,
changes would need to be made.  Some question of how (whether) to handle
registration of unmapped ranges, closest to say ->mm->def_flags=VM_MERGE.
My hunch is there's 2 cases users might care about, a specific range
(qemu-kvm, CERN app, etc) or the entire vma space of a process.  Another
question of what to do w/ VM_LOCKED, should that exclude VM_MERGE or
let user get what asked for?

thanks,
-chris
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