Re: [PATCH 5/5] Swapless V2: Revise main migration logic

[Christoph Lameter <clameter@sgi.com>]

Hmmm... Good ideas. I think it could be much simpler like the following 
patch.

However, the problem here is how to know that we really took the anon_vma 
lock and what to do about a page being unmmapped while migrating. This 
could cause the anon_vma not to be unlocked.

I guess we would need to have try_to_unmap return some state information.
I also toyed around with writing an "install_migration_ptes" function 
which would be called only for anonymous pages and would reduce the 
changes to try_to_unmap(). However, that also got too complicated.

Index: linux-2.6.17-rc1-mm2/mm/migrate.c
===================================================================
--- linux-2.6.17-rc1-mm2.orig/mm/migrate.c	2006-04-17 17:21:08.000000000 -0700
+++ linux-2.6.17-rc1-mm2/mm/migrate.c	2006-04-17 23:53:32.000000000 -0700
@@ -236,7 +233,6 @@ static void remove_migration_ptes(struct
 	 * We hold the mmap_sem lock. So no need to call page_lock_anon_vma.
 	 */
 	anon_vma = (struct anon_vma *) (mapping - PAGE_MAPPING_ANON);
-	spin_lock(&anon_vma->lock);
 
 	list_for_each_entry(vma, &anon_vma->head, anon_vma_node)
 		remove_migration_pte(vma, page_address_in_vma(new, vma),
Index: linux-2.6.17-rc1-mm2/mm/rmap.c
===================================================================
--- linux-2.6.17-rc1-mm2.orig/mm/rmap.c	2006-04-17 17:21:08.000000000 -0700
+++ linux-2.6.17-rc1-mm2/mm/rmap.c	2006-04-17 23:53:39.000000000 -0700
@@ -723,7 +723,8 @@ static int try_to_unmap_anon(struct page
 		if (ret == SWAP_FAIL || !page_mapped(page))
 			break;
 	}
-	spin_unlock(&anon_vma->lock);
+	if (!migration)
+		spin_unlock(&anon_vma->lock);
 	return ret;
 }
 

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