Re: [RFC 2.6.11-rc2-mm2 7/7] mm: manual page migration -- sys_page_migrate

[Ray Bryant <raybry@sgi.com>]

Dave Hansen wrote:
> On Tue, 2005-02-15 at 04:50 -0600, Robin Holt wrote:
> 
>>What is the fundamental opposition to an array from from-to node mappings?
>>They are not that difficult to follow.  They make the expensive traversal
>>of ptes the single pass operation.  The time to scan the list of from nodes
>>to locate the node this page belongs to is relatively quick when compared
>>to the time to scan ptes and will result in probably no cache trashing
>>like the long traversal of all ptes in the system required for multiple
>>system calls.  I can not see the node array as anything but the right way
>>when compared to multiple system calls.  What am I missing?
> 
> 
> I don't really have any fundamental opposition.  I'm just trying to make
> sure that there's not a simpler (better) way of doing it.  You've
> obviously thought about it a lot more than I have, and I'm trying to
> understand your process.
> 
> As far as the execution speed with a simpler system call.  Yes, it will
> likely be slower.  However, I'm not sure that the increase in scan time
> is all that significant compared to the migration code (it's pretty
> slow).
> 
> -- Dave
> 
> 
I'm worried about doing all of those find_get_page() things over and over
when the mapped file we are migrating is large.  I suppose one can argue
that that is never going to be the case (e. g. no one in their right mind
would migrate a job with a 300 GB mapped file).  So we are back to the
overlapping set of nodes issue.  Let me look into this some more.

-- 
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Ray Bryant
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