mm: lru interface change

Add Wired list to LRU.
Add PG_Wired bit to page.

mm/swap.c +29 -5

+	if(!PageWired(page)){
+		if(PageLRU(page)){
+			del_page_from_lru(zone, page);
+			add_page_to_wired_list(zone,page);
+			SetPageWired(page);
+		}
+	}
+	spin_unlock_irq(&zone->lru_lock);
+}
+
+/* Unwire the page.
+ * If it isnt wired by any process, try move it to active list.
+ */
+void fastcall unwire_page(struct page *page)
+{
+	struct zone *zone = page_zone(page);
+
+	spin_lock_irq(&zone->lru_lock);
+	page->wired_count --;
+	if(!page->wired_count){
+		if(PageLRU(page) && TestClearPageWired(page)){
+			del_page_from_wired_list(zone,page);
+			add_page_to_active_list(zone,page);
+			SetPageActive(page);
+		}
+	}
+	spin_unlock_irq(&zone->lru_lock);
+}
+
 /*
  * Mark a page as having seen activity.
  *

@@ -119,11 +157,13 @@
  */
 void fastcall mark_page_accessed(struct page *page)
 {
-	if (!PageActive(page) && PageReferenced(page) && PageLRU(page)) {
-		activate_page(page);
-		ClearPageReferenced(page);
-	} else if (!PageReferenced(page)) {
-		SetPageReferenced(page);

mm/swap.c +3 -4

@@ -178,13 +218,15 @@
 	struct zone *zone = page_zone(page);
 
 	spin_lock_irqsave(&zone->lru_lock, flags);
-	if (TestClearPageLRU(page))
-		del_page_from_lru(zone, page);
-	if (page_count(page) != 0)
-		page = NULL;
+	if(!PageWired(page)) {
+		if (TestClearPageLRU(page))
+			del_page_from_lru(zone, page);

mm/swap.c line 121

Quoted 1 line

mm/swap.c +1 -0

+	page->wired_count ++;

Oh dear, I missed this change you made to struct page, tucked away in 5/8. This alone pretty much makes it a showstopper, I'm afraid. You'll have to work out some other way to do it so as not to penalise 99.999% of machines which don't need this.

(Oh, and making the field a short usually won't help either, because of alignment constraints).

I may have missed something very trivial, but... why are they on a list at all if they don't get scanned

Quoted 3 lines · Stone Wang

Add Wired list to LRU.
Add PG_Wired bit to page.

I may have missed something very trivial, but... why are they on a list at all if they don't get scanned?

mm/swap.c 2006-03-07 11:45:37.000000000 -0500 line 116

Quoted 11 lines

diff -urN linux-2.6.15.orig/mm/swap.c linux-2.6.15/mm/swap.c

mm/swap.c 2006-03-07 11:45:37.000000000 -0500 renamed from mm/swap.c 2006-01-02 22:21:10.000000000 -0500 +4 -0

@@ -110,6 +110,44 @@
      spin_unlock_irq(&zone->lru_lock);
 }
 
+/* Wire the page; if the page is in LRU,
+ * try move it to Wired list.
+ */
+void fastcall wire_page(struct page *page)

Ahh, here's the elusive beast.

mm/swap.c 2006-03-07 11:45:37.000000000 -0500 line 120

Quoted 4 lines

mm/swap.c 2006-03-07 11:45:37.000000000 -0500 renamed from mm/swap.c 2006-01-02 22:21:10.000000000 -0500 +4 -0

+{
+     struct zone *zone = page_zone(page);
+
+     spin_lock_irq(&zone->lru_lock);

This is a fairly heavy lock for something which is going into page fault fastpaths and such. You might be better off making wired_count atomic and not using a lock in the common case if possible (even if it is only for mlocked pages, I'm sure someone will complain).

mm/swap.c 2006-03-07 11:45:37.000000000 -0500 line 121

Quoted 1 line

mm/swap.c 2006-03-07 11:45:37.000000000 -0500 renamed from mm/swap.c 2006-01-02 22:21:10.000000000 -0500 +1 -0

+     page->wired_count ++;

Oh dear, I missed this change you made to struct page, tucked away in 5/8. This alone pretty much makes it a showstopper, I'm afraid. You'll have to work out some other way to do it so as not to penalise 99.999% of machines which don't need this.

(Oh, and making the field a short usually won't help either, because of alignment constraints).

Quoted 41 lines

mm/swap.c 2006-03-07 11:45:37.000000000 -0500 renamed from mm/swap.c 2006-01-02 22:21:10.000000000 -0500 +29 -5

+     if(!PageWired(page)){
+             if(PageLRU(page)){
+                     del_page_from_lru(zone, page);
+                     add_page_to_wired_list(zone,page);
+                     SetPageWired(page);
+             }
+     }
+     spin_unlock_irq(&zone->lru_lock);
+}
+
+/* Unwire the page.
+ * If it isnt wired by any process, try move it to active list.
+ */
+void fastcall unwire_page(struct page *page)
+{
+     struct zone *zone = page_zone(page);
+
+     spin_lock_irq(&zone->lru_lock);
+     page->wired_count --;
+     if(!page->wired_count){
+             if(PageLRU(page) && TestClearPageWired(page)){
+                     del_page_from_wired_list(zone,page);
+                     add_page_to_active_list(zone,page);
+                     SetPageActive(page);
+             }
+     }
+     spin_unlock_irq(&zone->lru_lock);
+}
+
 /*
  * Mark a page as having seen activity.
  *

@@ -119,11 +157,13 @@
  */
 void fastcall mark_page_accessed(struct page *page)
 {
-     if (!PageActive(page) && PageReferenced(page) && PageLRU(page)) {
-             activate_page(page);
-             ClearPageReferenced(page);
-     } else if (!PageReferenced(page)) {
-             SetPageReferenced(page);

mm/swap.c 2006-03-07 11:45:37.000000000 -0500 line 169

Quoted 10 lines

mm/swap.c 2006-03-07 11:45:37.000000000 -0500 renamed from mm/swap.c 2006-01-02 22:21:10.000000000 -0500 +7 -0

+     if(!PageWired(page)) {
+             if (!PageActive(page) && PageReferenced(page) && PageLRU(page)) {
+                     activate_page(page);
+                     ClearPageReferenced(page);
+             } else if (!PageReferenced(page)) {
+                     SetPageReferenced(page);
+             }
      }
 }
 

So, umm... what happens when the page gets wired before activate_page()?

Quoted 11 lines

mm/swap.c 2006-03-07 11:45:37.000000000 -0500 renamed from mm/swap.c 2006-01-02 22:21:10.000000000 -0500 +3 -4

@@ -178,13 +218,15 @@
      struct zone *zone = page_zone(page);
 
      spin_lock_irqsave(&zone->lru_lock, flags);
-     if (TestClearPageLRU(page))
-             del_page_from_lru(zone, page);
-     if (page_count(page) != 0)
-             page = NULL;
+     if(!PageWired(page)) {
+             if (TestClearPageLRU(page))
+                     del_page_from_lru(zone, page);

mm/swap.c 2006-03-07 11:45:37.000000000 -0500 line 231

Quoted 10 lines

mm/swap.c 2006-03-07 11:45:37.000000000 -0500 renamed from mm/swap.c 2006-01-02 22:21:10.000000000 -0500 +5 -2

+             if (page_count(page) != 0)
+                     page = NULL;
+             if (page)
+                     free_hot_page(page);
+     }
      spin_unlock_irqrestore(&zone->lru_lock, flags);
-     if (page)
-             free_hot_page(page);
 }
 

Hmm... how do PageWired pages get freed, then?

mm/swap.c 2006-03-07 11:45:37.000000000 -0500 line 263

Quoted 11 lines

mm/swap.c 2006-03-07 11:45:37.000000000 -0500 renamed from mm/swap.c 2006-01-02 22:21:10.000000000 -0500 +2 -1

 EXPORT_SYMBOL(__page_cache_release);

@@ -214,7 +256,8 @@
 
              if (!put_page_testzero(page))
                      continue;
-
+             if(PageWired(page))
+                     continue;
              pagezone = page_zone(page);
              if (pagezone != zone) {
                      if (zone)

Ditto.

--
SUSE Labs, Novell Inc.

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Quoted 2 lines

I may have missed something very trivial, but... why are they on a list at all if they don't get scanned

Get the locked pages on a list is necessary for page management, scatter the locked pages around isnt a good idea.

Also, we could add some kinds of scan to the locked pages, if we find that it's necessary.