[PATCH 6/6] Direct Migration V3: SWAP_REFERENCE for try_to_unmap()

[Christoph Lameter]

Distinguish in try_to_umap_one between the case when the page is truly
unswappable from the case when the page was recently referenced.

The page migration code uses try_to_unmap_one and can avoid calling
try_to_unmap again if there was a persistent failure.

Signed-off-by: Christoph Lameter <clameter@xxxxxxx>

Index: linux-2.6.15-rc1-mm2/include/linux/rmap.h
===================================================================
--- linux-2.6.15-rc1-mm2.orig/include/linux/rmap.h	2005-11-18 12:28:37.000000000 -0800
+++ linux-2.6.15-rc1-mm2/include/linux/rmap.h	2005-11-18 12:28:44.000000000 -0800
@@ -122,6 +122,7 @@ unsigned long page_address_in_vma(struct
  */
 #define SWAP_SUCCESS	0
 #define SWAP_AGAIN	1
-#define SWAP_FAIL	2
+#define SWAP_REFERENCE	2
+#define SWAP_FAIL	3
 
 #endif	/* _LINUX_RMAP_H */
Index: linux-2.6.15-rc1-mm2/mm/rmap.c
===================================================================
--- linux-2.6.15-rc1-mm2.orig/mm/rmap.c	2005-11-18 12:28:37.000000000 -0800
+++ linux-2.6.15-rc1-mm2/mm/rmap.c	2005-11-18 12:28:44.000000000 -0800
@@ -552,15 +552,20 @@ static int try_to_unmap_one(struct page 
 
 	/*
 	 * If the page is mlock()d, we cannot swap it out.
-	 * If it's recently referenced (perhaps page_referenced
-	 * skipped over this mm) then we should reactivate it.
 	 */
-	if ((vma->vm_flags & VM_LOCKED) ||
-			ptep_clear_flush_young(vma, address, pte)) {
+	if (vma->vm_flags & VM_LOCKED) {
 		ret = SWAP_FAIL;
 		goto out_unmap;
 	}
 
+	/* If the page is recently referenced (perhaps page_referenced
+	 * skipped over this mm) then we should reactivate it.
+ 	 */
+	if (ptep_clear_flush_young(vma, address, pte)) {
+		ret = SWAP_REFERENCE;
+		goto out_unmap;
+	}
+
 	/* Nuke the page table entry. */
 	flush_cache_page(vma, address, page_to_pfn(page));
 	pteval = ptep_clear_flush(vma, address, pte);
@@ -710,7 +715,9 @@ static int try_to_unmap_anon(struct page
 
 	list_for_each_entry(vma, &anon_vma->head, anon_vma_node) {
 		ret = try_to_unmap_one(page, vma);
-		if (ret == SWAP_FAIL || !page_mapped(page))
+		if (ret == SWAP_FAIL ||
+		    ret == SWAP_REFERENCE ||
+		    !page_mapped(page))
 			break;
 	}
 	spin_unlock(&anon_vma->lock);
@@ -741,7 +748,9 @@ static int try_to_unmap_file(struct page
 	spin_lock(&mapping->i_mmap_lock);
 	vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
 		ret = try_to_unmap_one(page, vma);
-		if (ret == SWAP_FAIL || !page_mapped(page))
+		if (ret == SWAP_FAIL ||
+		    ret == SWAP_REFERENCE ||
+		    !page_mapped(page))
 			goto out;
 	}
 
@@ -823,7 +832,9 @@ out:
  *
  * SWAP_SUCCESS	- we succeeded in removing all mappings
  * SWAP_AGAIN	- we missed a mapping, try again later
+ * SWAP_REFERENCE - the page was recently referenced
  * SWAP_FAIL	- the page is unswappable
+ *
  */
 int try_to_unmap(struct page *page)
 {
Index: linux-2.6.15-rc1-mm2/mm/vmscan.c
===================================================================
--- linux-2.6.15-rc1-mm2.orig/mm/vmscan.c	2005-11-18 12:28:41.000000000 -0800
+++ linux-2.6.15-rc1-mm2/mm/vmscan.c	2005-11-18 12:28:44.000000000 -0800
@@ -470,6 +470,7 @@ static int shrink_list(struct list_head 
 		 */
 		if (page_mapped(page) && mapping) {
 			switch (try_to_unmap(page)) {
+			case SWAP_REFERENCE:
 			case SWAP_FAIL:
 				goto activate_locked;
 			case SWAP_AGAIN:
@@ -709,8 +710,9 @@ int migrate_page_remove_references(struc
 	for(i = 0; i < 10 && page_mapped(page); i++) {
 		int rc = try_to_unmap(page);
 
-		if (rc == SWAP_SUCCESS)
+		if (rc == SWAP_SUCCESS || rc == SWAP_FAIL)
 			break;
+
 		/*
 		 * If there are other runnable processes then running
 		 * them may make it possible to unmap the page
-
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