Re: Selective swap out of processes

[Dave Hansen <haveblue@us.ibm.com>]

I need the same basic thing for process checkpoint/restart.  I just have
a syscall to which I give a virtual address, and then have the kernel
try to swap it out.  It uses follow_page(FOLL_GET) and find_vma() in the
higher-level function, but this appears to work just fine.

I meant this as a horrible hack to play with a couple of months ago, but
it hasn't quite broken on me, yet.  


diff -puN mm/vmscan.c~ptrace-force-swap1 mm/vmscan.c
--- lxc/mm/vmscan.c~ptrace-force-swap1  2007-03-15 11:21:06.000000000 -0700
+++ lxc-dave/mm/vmscan.c        2007-03-15 13:03:57.000000000 -0700
@@ -614,6 +614,23 @@ static unsigned long shrink_page_list(st        return nr_reclaimed;    
 } 
 
+int try_to_put_page_in_swap(struct page *page)
+{
+
+       get_page(page);
+       if (page_count(page) == 1)
+                /* page was freed from under us. So we are done. */
+                return -EAGAIN;
+       lock_page(page);
+       if (PageWriteback(page))
+               wait_on_page_writeback(page);
+       try_to_unmap(page, 0);
+       //printk("page mapped: %d\n", page_mapped(page));
+       unlock_page(page);
+       put_page(page);
+       return 0;
+}      
+
 /*     
  * zone->lru_lock is heavily contended.  Some of the functions that
  * shrink the lists perform better by taking out a batch of pages

-- Dave

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