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

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Date:	Thu, 2 Apr 2009 16:41:18 +0200
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Chris Wright <chrisw@...hat.com>
Cc:	Anthony Liguori <anthony@...emonkey.ws>,
	Izik Eidus <ieidus@...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

On Wed, Apr 01, 2009 at 10:31:14PM -0700, Chris Wright wrote:
>   - 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

The unregister cleanup must happen at the vma level (with unregister
when vma goes away or is overwritten) for this to provide sane madvise
semantics (not just in exit/exec, but in unmap/mmap too). Otherwise
this is all but madvise. Basically we need a chunk of code in core VM
when KSM=y/m, even if we keep returning -EINVAL when KSM=n (for
backwards compatibility, -ENOSYS not). Example, vma must be split in
two if you MAP_SHARABLE only part of it etc...
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