[PATCH] VM fix + performance boost

[Rik van Riel <riel@nl.linux.org>]

Hi Alan,

here's the latest version of my VM improvement patch.
I suspect this will be the final version since I have
not been able to crash a machine with this patch and
neither have a bunch of other people. If nobody manages
to crash it, could you please include it in 2.2.15?

Other people:  this thing might get included in 2.2.15,
could you please please test it and try if you can break
it? If it still is breakable, I'll fix the bug before
2.2.15 is shipped...

The patch is against 2.2.15-pre3.

regards,

Rik
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--- linux-2.2.15-pre3/mm/vmscan.c.orig	Wed Jan 19 21:18:54 2000
+++ linux-2.2.15-pre3/mm/vmscan.c	Fri Jan 21 16:30:55 2000
@@ -64,6 +64,14 @@
 		return 0;
 
 	/*
+	 * By setting this bit shrink_mmap() will do
+	 * second-chance page replacement, only do this
+	 * when we are the only (non-pagecache) user.
+	 */
+	if (atomic_read(&page_map->count) <= 2)
+		set_bit(PG_referenced, &page_map->flags);
+
+	/*
 	 * Is the page already in the swap cache? If so, then
 	 * we can just drop our reference to it without doing
 	 * any IO - it's already up-to-date on disk.
@@ -437,7 +445,7 @@
        printk ("Starting kswapd v%.*s\n", i, s);
 }
 
-static struct wait_queue * kswapd_wait = NULL;
+struct wait_queue * kswapd_wait = NULL;
 
 /*
  * The background pageout daemon, started as a kernel thread
@@ -485,41 +493,26 @@
 		 * the processes needing more memory will wake us
 		 * up on a more timely basis.
 		 */
-		interruptible_sleep_on_timeout(&kswapd_wait, HZ);
 		while (nr_free_pages < freepages.high)
 		{
-			if (do_try_to_free_pages(GFP_KSWAPD))
-			{
-				if (tsk->need_resched)
-					schedule();
-				continue;
-			}
-			tsk->state = TASK_INTERRUPTIBLE;
-			schedule_timeout(10*HZ);
+			if (!do_try_to_free_pages(GFP_KSWAPD))
+				break;
+			if (tsk->need_resched)
+				schedule();
 		}
+		run_task_queue(&tq_disk);
+		interruptible_sleep_on_timeout(&kswapd_wait, HZ);
 	}
 }
 
 /*
- * Called by non-kswapd processes when they want more
- * memory.
- *
- * In a perfect world, this should just wake up kswapd
- * and return. We don't actually want to swap stuff out
- * from user processes, because the locking issues are
- * nasty to the extreme (file write locks, and MM locking)
- *
- * One option might be to let kswapd do all the page-out
- * and VM page table scanning that needs locking, and this
- * process thread could do just the mmap shrink stage that
- * can be done by just dropping cached pages without having
- * any deadlock issues.
+ * Called by non-kswapd processes when kswapd really cannot
+ * keep up with the demand for free memory.
  */
 int try_to_free_pages(unsigned int gfp_mask)
 {
 	int retval = 1;
 
-	wake_up_interruptible(&kswapd_wait);
 	if (gfp_mask & __GFP_WAIT)
 		retval = do_try_to_free_pages(gfp_mask);
 	return retval;
--- linux-2.2.15-pre3/mm/page_alloc.c.orig	Wed Jan 19 21:32:05 2000
+++ linux-2.2.15-pre3/mm/page_alloc.c	Fri Jan 21 05:02:13 2000
@@ -20,6 +20,7 @@
 
 int nr_swap_pages = 0;
 int nr_free_pages = 0;
+extern struct wait_queue * kswapd_wait;
 
 /*
  * Free area management
@@ -184,8 +185,6 @@
 	atomic_set(&map->count, 1); \
 } while (0)
 
-int low_on_memory = 0;
-
 unsigned long __get_free_pages(int gfp_mask, unsigned long order)
 {
 	unsigned long flags;
@@ -212,21 +211,21 @@
 	if (!(current->flags & PF_MEMALLOC)) {
 		int freed;
 
-		if (nr_free_pages > freepages.min) {
-			if (!low_on_memory)
-				goto ok_to_allocate;
-			if (nr_free_pages >= freepages.high) {
-				low_on_memory = 0;
-				goto ok_to_allocate;
-			}
+		if (nr_free_pages <= freepages.low) {
+			wake_up_interruptible(&kswapd_wait);
+			/* a bit of defensive programming */
+			if (gfp_mask & __GFP_WAIT)
+				schedule();
 		}
+		if (nr_free_pages > freepages.min)
+			goto ok_to_allocate;
 
-		low_on_memory = 1;
+		/* Danger, danger! Do something or fail */
 		current->flags |= PF_MEMALLOC;
 		freed = try_to_free_pages(gfp_mask);
 		current->flags &= ~PF_MEMALLOC;
 
-		if (!freed && !(gfp_mask & (__GFP_MED | __GFP_HIGH)))
+		if (!freed && !(gfp_mask & __GFP_HIGH))
 			goto nopage;
 	}
 ok_to_allocate:

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