[PATCH] Page Migration: Make do_swap_page redo the fault

It is better to redo the complete fault if do_swap_page() finds that the
page is not in PageSwapCache() because the page migration code may have
replaced the swap pte already with a pte pointing to valid memory.

do_swap_page() may interpret an invalid swap entry without this patch
because we do not reload the pte if we are looping back.  The page
migration code may already have reused the swap entry referenced by our
local swp_entry.

Signed-off-by: Christoph Lameter <clameter@sgi.com>
Cc: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

mm/memory.c

@@ -1879,7 +1879,6 @@ static int do_swap_page(struct mm_struct *mm, struct vm_area_struct *vma,
 		goto out;
 
 	entry = pte_to_swp_entry(orig_pte);
-again:
 	page = lookup_swap_cache(entry);
 	if (!page) {
  		swapin_readahead(entry, address, vma);
@@ -1903,12 +1902,6 @@ again:
 
 	mark_page_accessed(page);
 	lock_page(page);
-	if (!PageSwapCache(page)) {
-		/* Page migration has occured */
-		unlock_page(page);
-		page_cache_release(page);
-		goto again;
-	}
 
 	/*
 	 * Back out if somebody else already faulted in this pte.