Date: Mon, 14 Feb 2005 16:01:49 -0600
From: Robin Holt <holt@sgi.com>
To: Dave Hansen <haveblue@us.ibm.com>
Cc: Robin Holt <holt@sgi.com>, Ray Bryant <raybry@sgi.com>,
       Hirokazu Takahashi <taka@valinux.co.jp>,
       Hugh DIckins <hugh@veritas.com>, Andrew Morton <akpm@osdl.org>,
       Marcello Tosatti <marcello@cyclades.com>,
       Ray Bryant <raybry@austin.rr.com>, linux-mm <linux-mm@kvack.org>,
       linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [RFC 2.6.11-rc2-mm2 7/7] mm: manual page migration -- sys_page_migrate
Message-ID: <20050214220148.GA11832@lnx-holt.americas.sgi.com>
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On Mon, Feb 14, 2005 at 10:50:42AM -0800, Dave Hansen wrote:
> On Mon, 2005-02-14 at 07:52 -0600, Robin Holt wrote:
> > The node mask is a list of allowed.  This is intended to be as near
> > to a one-to-one migration path as possible.
> 
> If that's the case, it would make the kernel internals a bit simpler to
> only take a "from" and "to" node, instead of those maps.  You'll end up
> making multiple syscalls, but that shouldn't be a problem.  

Then how do you handle overlapping nodes.  If I am doing a 5->4, 4->3,
3->2, 2->1 shift in the memory placement and had only a from and to node,
I would end up calling multiple times.  This would end up in memory shifting
from 5->4 on the first, 4->3 on the second, ... with the end result of
all memory shifting to a single node.

With the array-of-node maps, you make a single pass across the address
space.  This results in a clean mapping without the userspace needing to
know which nodes the pages are on.

On a seperate topic, I would guess the syscall time is trivial compared
to the time to walk the page tables.

Thanks,
Robin
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