Date: Wed, 27 Feb 2008 14:43:41 -0800 (PST)
From: Christoph Lameter <clameter@sgi.com>
To: Nick Piggin <nickpiggin@yahoo.com.au>
cc: akpm@linux-foundation.org, Andrea Arcangeli <andrea@qumranet.com>,
       Robin Holt <holt@sgi.com>, Avi Kivity <avi@qumranet.com>,
       Izik Eidus <izike@qumranet.com>, kvm-devel@lists.sourceforge.net,
       Peter Zijlstra <a.p.zijlstra@chello.nl>, general@lists.openfabrics.org,
       Steve Wise <swise@opengridcomputing.com>,
       Roland Dreier <rdreier@cisco.com>, Kanoj Sarcar <kanojsarcar@yahoo.com>,
       steiner@sgi.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org,
       daniel.blueman@quadrics.com
Subject: Re: [patch 5/6] mmu_notifier: Support for drivers with revers maps
 (f.e. for XPmem)
In-Reply-To: <200802201055.21343.nickpiggin@yahoo.com.au>
Message-ID: <Pine.LNX.4.64.0802271440530.13186@schroedinger.engr.sgi.com>
References: <20080215064859.384203497@sgi.com> <20080215064933.376635032@sgi.com>
 <200802201055.21343.nickpiggin@yahoo.com.au>
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On Wed, 20 Feb 2008, Nick Piggin wrote:

> I don't know how this is supposed to solve anything. The sleeping
> problem happens I guess mostly in truncate. And all you are doing
> is putting these rmap callbacks in page_mkclean and try_to_unmap.

truncate is handled by the range invalidates. This is special code to deal 
with the unnap/clean of an individual page.

> That doesn't seem right. To start with, the new callbacks aren't
> even called in the places where invalidate_page isn't allowed to
> sleep.
> 
> The problem is unmap_mapping_range, right? And unmap_mapping_range
> must walk the rmaps with the mmap lock held, which is why it can't
> sleep. And it can't hold any mmap_sem so it cannot prevent address

Nope. unmap_mapping_range is already handled by the range callbacks.

> So in the meantime, you could have eg. a fault come in and set up a
> new page for one of the processes, and that page might even get
> exported via the same external driver. And now you have a totally
> inconsistent view.

The situation that you are imagining has already been dealt with by the 
earlier patches. This is only to allow sleeping while unmapping individual 
pages.
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