linux-kernel - Re: [patch 0/6] MMU Notifiers V6

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Message-ID: <20080208233636.GG26564@sgi.com>
Date:	Fri, 8 Feb 2008 17:36:37 -0600
From:	Robin Holt <holt@....com>
To:	Christoph Lameter <clameter@....com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, andrea@...ranet.com,
	holt@....com, avi@...ranet.com, izike@...ranet.com,
	kvm-devel@...ts.sourceforge.net, a.p.zijlstra@...llo.nl,
	steiner@....com, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	daniel.blueman@...drics.com, general@...ts.openfabrics.org
Subject: Re: [patch 0/6] MMU Notifiers V6

On Fri, Feb 08, 2008 at 03:32:19PM -0800, Christoph Lameter wrote:
> On Fri, 8 Feb 2008, Andrew Morton wrote:
> 
> > What about ib_umem_get()?
> 
> Ok. It pins using an elevated refcount. Same as XPmem right now. With that 
> we effectively pin a page (page migration will fail) but we will 
> continually be reclaiming the page and may repeatedly try to move it. We 
> have issues with XPmem causing too many pages to be pinned and thus the 
> OOM getting into weird behavior modes (OOM or stop lru scanning due to 
> all_reclaimable set).
> 
> An elevated refcount will also not be noticed by any of the schemes under 
> consideration to improve LRU scanning performance.

Christoph, I am not sure what you are saying here.  With v4 and later,
I thought we were able to use the rmap invalidation to remove the ref
count that XPMEM was holding and therefore be able to swapout.  Did I miss
something?  I agree the existing XPMEM does pin.  I hope we are not saying
the XPMEM based upon these patches will not be able to swap/migrate.

Thanks,
Robin
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