[PATCH] VM bugfix + rebalanced + code beauty

[PATCH] VM bugfix + rebalanced + code beauty

[Rik van Riel]

Hi evil7, Alan,

here is a patch (versus 2.4.0-test1-ac5 and 6) that fixes a number
of things in the VM subsystem.

- since the pagecache can now contain dirty pages, we no
  longer take them out of the pagecache when they get dirtied
- the aging code is beautified and better readable
- don't start IO on a page from the wrong zone (in shrink_mmap),
  this should make the stalls less
- in __alloc_pages(), wake up kswapd when zone->zone_wake_kswapd
  is set for *all* zones, and keep waking it up until it is reset
  for at least one zone   (the rinse, leather, repeat algorithm
  should give us proper balancing between zones here)
- keep a smaller percentage of highmem pages free
- don't give up so early in __alloc_pages ... as long as there is
  still hope, we keep trying; this should make VM more stable too

The biggest impact is the change where we wake up kswapd when
we should ... this makes kswapd do all the hard work in the
background so foreground applications can just continue with
the allocation without stalls. This will make kswapd use a
little bit more CPU, but since this reduces latency for your
applications a lot this is nothing to worry about.

I'm interested in situations where the code still does the
"wrong thing", but of course I'd also like to hear of any
success stories ;)

regards,

Rik
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--- linux-2.4.0-t1-ac5/mm/filemap.c.orig	Tue May 30 12:54:44 2000
+++ linux-2.4.0-t1-ac5/mm/filemap.c	Tue May 30 19:00:43 2000
@@ -56,6 +56,8 @@
 #define CLUSTER_PAGES		(1 << page_cluster)
 #define CLUSTER_OFFSET(x)	(((x) >> page_cluster) << page_cluster)
 
+#define min(a,b)		((a < b) ? a : b)
+
 void __add_page_to_hash_queue(struct page * page, struct page **p)
 {
 	atomic_inc(&page_cache_size);
@@ -265,19 +267,25 @@
 		list_del(page_lru);
 
 		if (PageTestandClearReferenced(page)) {
-			page->age += 3;
-			if (page->age > 10)
-				page->age = 10;
+			page->age += PG_AGE_ADV;
+			if (page->age > PG_AGE_MAX)
+				page->age = PG_AGE_MAX;
 			goto dispose_continue;
 		}
-		if (page->age)
-			page->age--;
+		page->age -= min(PG_AGE_DECL, page->age);
 
 		if (page->age)
 			goto dispose_continue;
 
 		count--;
 		/*
+		 * Page is from a zone we don't care about.
+		 * Don't drop page cache entries in vain.
+		 */
+		if (page->zone->free_pages > page->zone->pages_high)
+			goto dispose_continue;
+
+		/*
 		 * Avoid unscalable SMP locking for pages we can
 		 * immediate tell are untouchable..
 		 */
@@ -326,13 +334,6 @@
 			goto cache_unlock_continue;
 
 		/*
-		 * Page is from a zone we don't care about.
-		 * Don't drop page cache entries in vain.
-		 */
-		if (page->zone->free_pages > page->zone->pages_high)
-			goto cache_unlock_continue;
-
-		/*
 		 * Is it a page swap page? If so, we want to
 		 * drop it if it is no longer used, even if it
 		 * were to be marked referenced..
@@ -345,7 +346,7 @@
 			}
 			/* PageDeferswap -> we swap out the page now. */
 			if (gfp_mask & __GFP_IO)
-				goto async_swap;
+				goto async_swap_continue;
 			goto cache_unlock_continue;
 		}
 
@@ -368,7 +369,7 @@
 		UnlockPage(page);
 		page_cache_release(page);
 		goto dispose_continue;
-async_swap:
+async_swap_continue:
 		spin_unlock(&pagecache_lock);
 		/* Do NOT unlock the page ... that is done after IO. */
 		ClearPageDirty(page);
--- linux-2.4.0-t1-ac5/mm/memory.c.orig	Tue May 30 12:54:44 2000
+++ linux-2.4.0-t1-ac5/mm/memory.c	Tue May 30 18:59:36 2000
@@ -847,7 +847,7 @@
 			UnlockPage(old_page);
 			break;
 		}
-		delete_from_swap_cache_nolock(old_page);
+		SetPageDirty(old_page);
 		UnlockPage(old_page);
 		/* FallThrough */
 	case 1:
@@ -1058,7 +1058,7 @@
 	 */
 	lock_page(page);
 	swap_free(entry);
-	if (write_access && !is_page_shared(page)) {
+	if (write_access && !is_page_shared(page) && nr_free_highpages()) {
 		delete_from_swap_cache_nolock(page);
 		UnlockPage(page);
 		page = replace_with_highmem(page);
--- linux-2.4.0-t1-ac5/mm/page_alloc.c.orig	Tue May 30 12:54:44 2000
+++ linux-2.4.0-t1-ac5/mm/page_alloc.c	Tue May 30 19:26:06 2000
@@ -29,7 +29,7 @@
 pg_data_t *pgdat_list;
 
 static char *zone_names[MAX_NR_ZONES] = { "DMA", "Normal", "HighMem" };
-static int zone_balance_ratio[MAX_NR_ZONES] = { 128, 128, 128, };
+static int zone_balance_ratio[MAX_NR_ZONES] = { 128, 128, 512, };
 static int zone_balance_min[MAX_NR_ZONES] = { 10 , 10, 10, };
 static int zone_balance_max[MAX_NR_ZONES] = { 255 , 255, 255, };
 
@@ -141,10 +141,13 @@
 
 	spin_unlock_irqrestore(&zone->lock, flags);
 
-	if (zone->free_pages > zone->pages_high) {
-		zone->zone_wake_kswapd = 0;
+	if (zone->free_pages >= zone->pages_low) {
 		zone->low_on_memory = 0;
 	}
+
+	if (zone->free_pages >= zone->pages_high) {
+		zone->zone_wake_kswapd = 0;
+	}
 }
 
 #define MARK_USED(index, order, area) \
@@ -239,14 +242,16 @@
 			struct page *page = rmqueue(z, order);
 			if (z->free_pages < z->pages_low) {
 				z->zone_wake_kswapd = 1;
-				if (waitqueue_active(&kswapd_wait))
-					wake_up_interruptible(&kswapd_wait);
 			}
 			if (page)
 				return page;
 		}
 	}
 
+	/* All zones are in need of kswapd. */
+	if (waitqueue_active(&kswapd_wait))
+		wake_up_interruptible(&kswapd_wait);
+
 	/*
 	 * Ok, we don't have any zones that don't need some
 	 * balancing.. See if we have any that aren't critical..
@@ -258,7 +263,7 @@
 			break;
 		if (!z->low_on_memory) {
 			struct page *page = rmqueue(z, order);
-			if (z->free_pages < z->pages_min)
+			if (z->free_pages < (z->pages_min + z->pages_low) / 2)
 				z->low_on_memory = 1;
 			if (page)
 				return page;
@@ -279,7 +284,7 @@
 	}
 
 	/*
-	 * Final phase: allocate anything we can!
+	 * We freed something, so we're allowed to allocate anything we can!
 	 */
 	zone = zonelist->zones;
 	for (;;) {
@@ -294,6 +299,19 @@
 	}
 
 fail:
+	/* Last try, zone->low_on_memory isn't reset until we hit pages_low */
+	zone = zonelist->zones;
+	for (;;) {
+		zone_t *z = *(zone++);
+		int gfp_mask = zonelist->gfp_mask;
+		if (!z)
+			break;
+		if (z->free_pages > z->pages_min) {
+			struct page *page = rmqueue(z, order);
+			if (page)
+				return page;
+		}
+	}
 	/* No luck.. */
 	return NULL;
 }
--- linux-2.4.0-t1-ac5/include/linux/swap.h.orig	Tue May 30 14:29:42 2000
+++ linux-2.4.0-t1-ac5/include/linux/swap.h	Tue May 30 14:36:53 2000
@@ -161,6 +161,16 @@
 extern spinlock_t pagemap_lru_lock;
 
 /*
+ * Magic constants for page aging. If the system is programmed
+ * right, tweaking these should have almost no effect...
+ * The 2.4 code, however, is mostly simple and stable ;)
+ */
+#define PG_AGE_MAX	64
+#define PG_AGE_START	5
+#define PG_AGE_ADV	3
+#define PG_AGE_DECL	1
+
+/*
  * Helper macros for lru_pages handling.
  */
 #define	lru_cache_add(page)			\
@@ -168,7 +178,7 @@
 	spin_lock(&pagemap_lru_lock);		\
 	list_add(&(page)->lru, &lru_cache);	\
 	nr_lru_pages++;				\
-	page->age = 2;				\
+	page->age = PG_AGE_START;		\
 	SetPageActive(page);			\
 	spin_unlock(&pagemap_lru_lock);		\
 } while (0)

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Re: [PATCH] VM bugfix + rebalanced + code beauty

[Christoph Rohland]

Rik van Riel <riel@conectiva.com.br> writes:
> here is a patch (versus 2.4.0-test1-ac5 and 6) that fixes a number
> of things in the VM subsystem.
> 
> - since the pagecache can now contain dirty pages, we no
>   longer take them out of the pagecache when they get dirtied

Does this mean, that we can do anonymous shared maps in the page
cache?

Greetings
		Christoph
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Re: [PATCH] VM bugfix + rebalanced + code beauty

[Rik van Riel]

On 31 May 2000, Christoph Rohland wrote:
> Rik van Riel <riel@conectiva.com.br> writes:
> > here is a patch (versus 2.4.0-test1-ac5 and 6) that fixes a number
> > of things in the VM subsystem.
> > 
> > - since the pagecache can now contain dirty pages, we no
> >   longer take them out of the pagecache when they get dirtied
> 
> Does this mean, that we can do anonymous shared maps in the page
> cache?

Ermmm, %s/pagecache/swapcache/g in my email. My mistake...

regards,

Rik
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Re: [PATCH] VM bugfix + rebalanced + code beauty

[Rik van Riel]

On 31 May 2000, Christoph Rohland wrote:
> Rik van Riel <riel@conectiva.com.br> writes:
> > here is a patch (versus 2.4.0-test1-ac5 and 6) that fixes a number
> > of things in the VM subsystem.
> > 
> > - since the pagecache can now contain dirty pages, we no
> >   longer take them out of the pagecache when they get dirtied
> 
> Does this mean, that we can do anonymous shared maps in the page
> cache?

I'm testing stuff now, but seem unable to reproduce your
observation. However, I *am* seeing high cpu usage by
kswapd ;)

I guess we really want to integrate the SHM swapout routine
with shrink_mmap...

regards,

Rik
--
The Internet is not a network of computers. It is a network
of people. That is its real strength.

Wanna talk about the kernel?  irc.openprojects.net / #kernelnewbies
http://www.conectiva.com/		http://www.surriel.com/

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Re: [PATCH] VM bugfix + rebalanced + code beauty

[Christoph Rohland]

Rik van Riel <riel@conectiva.com.br> writes:

> I'm testing stuff now, but seem unable to reproduce your
> observation. However, I *am* seeing high cpu usage by
> kswapd ;)

I do these tests regularly 8way/8GB and the latest kernel is
definitely a step back.

> I guess we really want to integrate the SHM swapout routine
> with shrink_mmap...

I would love to integrate the whole shm page handling into the page
cache.

Greetings
		Christoph
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Re: [PATCH] VM bugfix + rebalanced + code beauty

[Rik van Riel]

On 31 May 2000, Christoph Rohland wrote:
> Rik van Riel <riel@conectiva.com.br> writes:
> 
> > I'm testing stuff now, but seem unable to reproduce your
> > observation. However, I *am* seeing high cpu usage by
> > kswapd ;)
> 
> I do these tests regularly 8way/8GB and the latest kernel is
> definitely a step back.

I have tracked down why. Shrink_mmap uses a bit more CPU
due to the page aging, but because we really want to free
an SHM page, shrink_mmap won't find anything suitable (yes,
aging works) and just waste some CPU before falling through
to shm_swap.

> > I guess we really want to integrate the SHM swapout routine
> > with shrink_mmap...
> 
> I would love to integrate the whole shm page handling into the
> page cache.

That would be great. If we have this we can weigh page cache,
swap cache and shm pages equally. Not only will this result in
better page replacement, but it will also save on kswapd cpu
usage.

Even better, having this will allow us to (trivially) insert
the active/inactive queue idea into the kernel, fixing the
"write stall" problems for a lot of situations.

regards,

Rik
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Re: [PATCH] VM bugfix + rebalanced + code beauty

[Christoph Rohland]

Rik van Riel <riel@conectiva.com.br> writes:

> > I would love to integrate the whole shm page handling into the
> > page cache.
> 
> That would be great. If we have this we can weigh page cache,
> swap cache and shm pages equally. Not only will this result in
> better page replacement, but it will also save on kswapd cpu
> usage.
> 
> Even better, having this will allow us to (trivially) insert
> the active/inactive queue idea into the kernel, fixing the
> "write stall" problems for a lot of situations.

And it will make shm trivial with respect to page handling. We will be
able to make the shm fs a real in memory fs which would be used
occasionally by SYSV shm.

Greetings
		Christoph
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