From: Christopher Yeoh <cyeoh@au1.ibm.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mm@kvack.org, Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [Resend] Cross Memory Attach v3 [PATCH]
Date: Mon, 21 Mar 2011 12:20:18 +1030 [thread overview]
Message-ID: <20110321122018.6306d067@lilo> (raw)
In-Reply-To: <20110317125427.eebbfb51.akpm@linux-foundation.org>
On Thu, 17 Mar 2011 12:54:27 -0700
Andrew Morton <akpm@linux-foundation.org> wrote:
> On Thu, 17 Mar 2011 15:40:26 +1030
> Christopher Yeoh <cyeoh@au1.ibm.com> wrote:
>
> > > Thinking out loud: if we had a way in which a process can add and
> > > remove a local anonymous page into pagecache then other processes
> > > could access that page via mmap. If both processes map the file
> > > with a nonlinear vma they they can happily sit there flipping
> > > pages into and out of the shared mmap at arbitrary file offsets.
> > > The details might get hairy ;) We wouldn't want all the regular
> > > mmap semantics of
> >
> > Yea, its the complexity of trying to do it that way that eventually
> > lead me to implementing it via a syscall and get_user_pages
> > instead, trying to keep things as simple as possible.
>
> The pagecache trick potentially gives zero-copy access, whereas the
> proposed code is single-copy. Although the expected benefits of that
> may not be so great due to TLB manipulation overheads.
>
> I worry that one day someone will come along and implement the
> pagecache trick, then we're stuck with obsolete code which we have to
> maintain for ever.
Perhaps I don't understand what you're saying correctly but I think that
one problem with the zero copy page flipping approach is that there
is no guarantee with the data that the MPI apps want to send
resides in a page or pages all by itself.
Regards,
Chris
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next prev parent reply other threads:[~2011-03-21 1:50 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-03-15 4:05 [Resend] Cross Memory Attach v3 [PATCH] Christopher Yeoh
2011-03-15 23:16 ` Andrew Morton
2011-03-17 5:10 ` Christopher Yeoh
2011-03-17 19:54 ` Andrew Morton
2011-03-21 1:50 ` Christopher Yeoh [this message]
2011-03-21 1:55 ` Andrew Morton
2011-03-21 2:15 ` Christopher Yeoh
2011-03-23 2:22 ` Christopher Yeoh
2011-03-23 22:50 ` Rusty Russell
2011-03-25 13:22 ` Christopher Yeoh
2011-04-12 0:48 ` Christopher Yeoh
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