linux-kernel - Re: [PATCH] ummunotify: Userspace support for MMU notifications

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Message-ID: <20100414085228.GL23554@redhat.com>
Date:	Wed, 14 Apr 2010 11:52:28 +0300
From:	Gleb Natapov <gleb@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Roland Dreier <rdreier@...co.com>,
	Håkon Bugge <Haakon.Bugge@....COM>,
	Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Eric B Munson <ebmunson@...ibm.com>,
	linux-kernel@...r.kernel.org, linux-rdma@...r.kernel.org,
	rolandd@...co.com, pavel@....cz, mingo@...e.hu, jsquyres@...co.com
Subject: Re: [PATCH] ummunotify: Userspace support for MMU notifications

On Tue, Apr 13, 2010 at 08:02:54PM +0200, Peter Zijlstra wrote:
> On Tue, 2010-04-13 at 10:57 -0700, Roland Dreier wrote:
> > Are those system calls the only possible way that virtual to physical
> > mappings can change?  Can't page migration or something like that
> > potentially affect things?  And even if you did have hooks into every
> > system call that mattered (keep in mind that relying on glibc is not
> > enough, since an MPI application may not use glibc) would decoding them
> > and figuring out what happened really be preferable to a single event
> > type that tells you exactly what address range was affected? 
> 
> Yeah, virtual<->physical maps can change through swapping, page
> migration, memory compaction, huge-page aggregation (the latter two not
> yet being upstream).
> 
> Even mlock() doesn't pin virtual<->physical maps.
Pages registered for RDMA are GUPed so no method above should touch
them. Fork+cow or unmap/map on the other hand can change
virtual<->physical maps. GUPed pages are still GUPed, but they are no
longer mapped into process' virtual address space. MPI copes with
Fork+cow by marking registered memory as MADV_DONTFORK.

--
			Gleb.
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