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

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Date:	Wed, 6 May 2009 17:36:51 +0100 (BST)
From:	Hugh Dickins <hugh@...itas.com>
To:	Chris Wright <chrisw@...hat.com>
cc:	Izik Eidus <ieidus@...hat.com>, Rik van Riel <riel@...hat.com>,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	aarcange@...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.

On Wed, 6 May 2009, Chris Wright wrote:
> 
> 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.

Good food for thought there, but not on my mind at this moment.

> Another
> question of what to do w/ VM_LOCKED, should that exclude VM_MERGE or
> let user get what asked for?

What's the issue with VM_LOCKED?  We wouldn't want to merge a page
while it was under get_user_pages (unless KSM's own, but ignore that),
but what's the deal with VM_LOCKED?

Is the phrase "covert channel" going to come up somehow?

Hugh
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