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Date: Mon, 14 Apr 2003 18:43:21 +0200
From: Antonio Vargas <wind@cocodriloo.com>
To: "Martin J. Bligh" <mbligh@aracnet.com>
Cc: Antonio Vargas <wind@cocodriloo.com>,
       Timothy Miller <tmiller10@cfl.rr.com>, linux-kernel@vger.kernel.org,
       nicoya@apia.dhs.org
Subject: Re: Quick question about hyper-threading (also some NUMA stuff)
Message-ID: <20030414164321.GE14552@wind.cocodriloo.com>
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On Mon, Apr 14, 2003 at 09:24:45AM -0700, Martin J. Bligh wrote:
> >> > Perhaps it would be good to un-COW pages:
> >> > 
> >> > 1. fork process
> >> > 2. if current node is not loaded, continue as usual
> >> > 3. if current node is loaded:
> >> > 3a. pick unloaded node
> >> > 4b. don't do COW for data pages, but simply copy them to node-local memory
> >> > 
> >> > This way, read-write sharings would be replicated for each node.
> >> 
> >> Sharing read-write stuff is a total nightmare - you have to deal with
> >> all the sync stuff, and invalidation. In real-life scenarios, I really
> >> doubt the complexity is worth it - read-only is quite complex enough,
> >> thanks ;-) 
> > 
> > I mean MAP_PRIVATE stuff, not MAP_SHARED.
> 
> OK, unless I misunderstand you, I think that happens naturally for that
> kind of thing - when we do the COW split, we'll get a node-local page
> by default (unless the local node is out of memory).
> 
> M.
�
IYes, it happens naturaly, but it's done when we try to write to it.
What I meant was, at fork time, it we are forking to a different node,
instead of COW-marking, do the COW-mark and the immediately do a sort-of
for_each_page(touch_as_if_written(page)), so that nodes would not have to
reference the memory from others.

I don't know if it's really usefull, and anyways I could not try to code it
unless there is a sort of NUMA simulator for "normal" machines.

Greets, Antonio.