On Fri, 2004-06-18 at 20:15, Ashwin Rao wrote:

The problem is the memory fragmentation. The code i am
writing is for the memory defragmentation as proposed
by Daniel Phillips, my project partner Alok mooley has
given mailed a simple prototype in the mid of feb.

Ahhh....  *That* code :)  Do you have an updated version you'd like to
share?  I'm curious how you integrated the suggestions from February.  

quoted

(*) Yes, I know the BKL isn't something you want to
grab if you can help it.

Isnt it a bad idea to take the BKL, the performance of
SMP systems will drastically be hampered.

Only during a defragment operation.  Are you planning to run the system
under constant defragmentation?

quoted

However, if we're on an unlikely error path or
similar and other options aren't suitable...

Maintaining atomicity in uniprocessor systems is easy
by preempt_enable and preempt_disable during the
operation. This implementation cannot be used for SMP
systems. 
Now during the time a page is copied/updatede if a
page is accessed the copied contents become invalid,
as updation is not done. Also during updation a
similar situation might arise.
The problem we are facing is to maintain the atomicity
of this operation on SMP boxes.

I think what you really want to do is keep anybody else from making a
new pte to the page, once you've invalidated all of the existing ones,
right?

Holding a lock_page() should do the trick.  Anybody that goes any pulls
the page out of the page cache has to do a lock_page() and check
page->mapping before they can establish a pte to it, so you can stop
that.  Since you're invalidating page->mapping before you move the page
(you *are* doing this, right?), it will end up working itself out.  

-- Dave

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