Re: [patch 2/2] xfs: use scalable vmap API

Re: [patch 2/2] xfs: use scalable vmap API

[Christoph Hellwig]

Hi Nick,

I've looked into retesting and re-enabling the swithc to your
scalabale vmap API (original commit 95f8e302c04c0b0c6de35ab399a5551605eeb006).

The good thing is that I can't reproduce the original regressions in
xfstests I've seen.  The bad news is that starting from the second
consequitive xfstests run we're not able to vmalloc the log buffers
anymore.  It seems the use of this API introduces some leak of vmalloc
space.  Any idea how to debug this further?

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Re: [patch 2/2] xfs: use scalable vmap API

[Nick Piggin]

On Tue, Jan 19, 2010 at 07:15:05AM -0500, Christoph Hellwig wrote:
> Hi Nick,
> 
> I've looked into retesting and re-enabling the swithc to your
> scalabale vmap API (original commit 95f8e302c04c0b0c6de35ab399a5551605eeb006).
> 
> The good thing is that I can't reproduce the original regressions in
> xfstests I've seen.  The bad news is that starting from the second
> consequitive xfstests run we're not able to vmalloc the log buffers
> anymore.  It seems the use of this API introduces some leak of vmalloc
> space.  Any idea how to debug this further?

Hi Christoph,

OK, that's worrying. It's silly have all that vmap layer work in the
tree and no users, not surprised to have a bug there.

Is this on a 32-bit system with small vmalloc area?

Basically in the scalable API implementation, we allocate per-CPU vmap
chunks (struct vmap_block) from the normal global allocator, and then
subsequently do allocations from those chunks using the simple bitmap
allocator.

Now there is more room for fragmentation with this approach, and a few
problems that I should really fix: firstly, a chunk with say a 1 page
hole left in it that is never used will never get freed. So it will be
good to free those chunks. Secondly, one CPU should be able to steal
from others if it can't find more memory.

So if you have small vmalloc space, it could be just these issues making
vmalloc consumption worse. Otherwise yes there could be a real leak there
unrelated to fragmentation.

When the vmap allocation fails, it would be good to basically see the
alloc_map and dirty_map for each of the vmap_blocks. This is going to be
a lot of information. Basically for all blocks with
free+dirty == VMAP_BBMAP_BITS are ones that could be released and you
could try the alloc again.

Thanks,
Nick

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Re: [patch 2/2] xfs: use scalable vmap API

[Christoph Hellwig]

On Mon, Jan 25, 2010 at 06:54:45PM +1100, Nick Piggin wrote:
> Is this on a 32-bit system with small vmalloc area?

Yes.

> When the vmap allocation fails, it would be good to basically see the
> alloc_map and dirty_map for each of the vmap_blocks. This is going to be
> a lot of information. Basically for all blocks with
> free+dirty == VMAP_BBMAP_BITS are ones that could be released and you
> could try the alloc again.

Any easy way to get them?  Sorry, not uptodate on your new vmalloc
implementation anymore.

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Re: [patch 2/2] xfs: use scalable vmap API

[Nick Piggin]

On Mon, Jan 25, 2010 at 03:17:50AM -0500, Christoph Hellwig wrote:
> On Mon, Jan 25, 2010 at 06:54:45PM +1100, Nick Piggin wrote:
> > Is this on a 32-bit system with small vmalloc area?
> 
> Yes.

OK, I would say it could easily be just due to fragmentation then.


> > When the vmap allocation fails, it would be good to basically see the
> > alloc_map and dirty_map for each of the vmap_blocks. This is going to be
> > a lot of information. Basically for all blocks with
> > free+dirty == VMAP_BBMAP_BITS are ones that could be released and you
> > could try the alloc again.
> 
> Any easy way to get them?  Sorry, not uptodate on your new vmalloc
> implementation anymore.

Let me try writing a few (tested) patches here first that I can send you.


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Re: [patch 2/2] xfs: use scalable vmap API

[Nick Piggin]

On Mon, Jan 25, 2010 at 07:33:09PM +1100, Nick Piggin wrote:
> > Any easy way to get them?  Sorry, not uptodate on your new vmalloc
> > implementation anymore.
> 
> Let me try writing a few (tested) patches here first that I can send you.

Well is it easy to reproduce the vmap failure? Here is a better tested
patch if you can try it. It fixes a couple of bugs and does some purging
of fragmented blocks.

If it does not help, can you tell me how many CPUs in your system?

Thanks,
Nick

--

Index: linux-2.6/mm/vmalloc.c
===================================================================
--- linux-2.6.orig/mm/vmalloc.c	2010-01-25 23:35:03.000000000 +1100
+++ linux-2.6/mm/vmalloc.c	2010-01-25 23:35:15.000000000 +1100
@@ -509,6 +509,9 @@ static unsigned long lazy_max_pages(void
 
 static atomic_t vmap_lazy_nr = ATOMIC_INIT(0);
 
+/* for per-CPU blocks */
+static void purge_fragmented_blocks_allcpus(void);
+
 /*
  * Purges all lazily-freed vmap areas.
  *
@@ -539,6 +542,9 @@ static void __purge_vmap_area_lazy(unsig
 	} else
 		spin_lock(&purge_lock);
 
+	if (sync)
+		purge_fragmented_blocks_allcpus();
+
 	rcu_read_lock();
 	list_for_each_entry_rcu(va, &vmap_area_list, list) {
 		if (va->flags & VM_LAZY_FREE) {
@@ -667,8 +673,6 @@ static bool vmap_initialized __read_most
 struct vmap_block_queue {
 	spinlock_t lock;
 	struct list_head free;
-	struct list_head dirty;
-	unsigned int nr_dirty;
 };
 
 struct vmap_block {
@@ -678,10 +682,9 @@ struct vmap_block {
 	unsigned long free, dirty;
 	DECLARE_BITMAP(alloc_map, VMAP_BBMAP_BITS);
 	DECLARE_BITMAP(dirty_map, VMAP_BBMAP_BITS);
-	union {
-		struct list_head free_list;
-		struct rcu_head rcu_head;
-	};
+	struct list_head free_list;
+	struct rcu_head rcu_head;
+	struct list_head purge;
 };
 
 /* Queue of free and dirty vmap blocks, for allocation and flushing purposes */
@@ -757,7 +760,7 @@ static struct vmap_block *new_vmap_block
 	vbq = &get_cpu_var(vmap_block_queue);
 	vb->vbq = vbq;
 	spin_lock(&vbq->lock);
-	list_add(&vb->free_list, &vbq->free);
+	list_add_rcu(&vb->free_list, &vbq->free);
 	spin_unlock(&vbq->lock);
 	put_cpu_var(vmap_block_queue);
 
@@ -776,8 +779,6 @@ static void free_vmap_block(struct vmap_
 	struct vmap_block *tmp;
 	unsigned long vb_idx;
 
-	BUG_ON(!list_empty(&vb->free_list));
-
 	vb_idx = addr_to_vb_idx(vb->va->va_start);
 	spin_lock(&vmap_block_tree_lock);
 	tmp = radix_tree_delete(&vmap_block_tree, vb_idx);
@@ -788,12 +789,61 @@ static void free_vmap_block(struct vmap_
 	call_rcu(&vb->rcu_head, rcu_free_vb);
 }
 
+static void purge_fragmented_blocks(int cpu)
+{
+	LIST_HEAD(purge);
+	struct vmap_block *vb;
+	struct vmap_block *n_vb;
+	struct vmap_block_queue *vbq = &per_cpu(vmap_block_queue, cpu);
+
+	rcu_read_lock();
+	list_for_each_entry_rcu(vb, &vbq->free, free_list) {
+
+		if (!(vb->free + vb->dirty == VMAP_BBMAP_BITS && vb->dirty != VMAP_BBMAP_BITS))
+			continue;
+
+		spin_lock(&vb->lock);
+		if (vb->free + vb->dirty == VMAP_BBMAP_BITS && vb->dirty != VMAP_BBMAP_BITS) {
+			vb->free = 0; /* prevent further allocs after releasing lock */
+			vb->dirty = VMAP_BBMAP_BITS; /* prevent purging it again */
+			bitmap_fill(vb->alloc_map, VMAP_BBMAP_BITS);
+			bitmap_fill(vb->dirty_map, VMAP_BBMAP_BITS);
+			spin_lock(&vbq->lock);
+			list_del_rcu(&vb->free_list);
+			spin_unlock(&vbq->lock);
+			spin_unlock(&vb->lock);
+			list_add_tail(&vb->purge, &purge);
+		} else
+			spin_unlock(&vb->lock);
+	}
+	rcu_read_unlock();
+
+	list_for_each_entry_safe(vb, n_vb, &purge, purge) {
+		list_del(&vb->purge);
+		free_vmap_block(vb);
+	}
+}
+
+static void purge_fragmented_blocks_thiscpu(void)
+{
+	purge_fragmented_blocks(smp_processor_id());
+}
+
+static void purge_fragmented_blocks_allcpus(void)
+{
+	int cpu;
+
+	for_each_possible_cpu(cpu)
+		purge_fragmented_blocks(cpu);
+}
+
 static void *vb_alloc(unsigned long size, gfp_t gfp_mask)
 {
 	struct vmap_block_queue *vbq;
 	struct vmap_block *vb;
 	unsigned long addr = 0;
 	unsigned int order;
+	int purge = 0;
 
 	BUG_ON(size & ~PAGE_MASK);
 	BUG_ON(size > PAGE_SIZE*VMAP_MAX_ALLOC);
@@ -806,24 +856,38 @@ again:
 		int i;
 
 		spin_lock(&vb->lock);
+		if (vb->free < 1UL << order)
+			goto next;
+
 		i = bitmap_find_free_region(vb->alloc_map,
 						VMAP_BBMAP_BITS, order);
 
-		if (i >= 0) {
-			addr = vb->va->va_start + (i << PAGE_SHIFT);
-			BUG_ON(addr_to_vb_idx(addr) !=
-					addr_to_vb_idx(vb->va->va_start));
-			vb->free -= 1UL << order;
-			if (vb->free == 0) {
-				spin_lock(&vbq->lock);
-				list_del_init(&vb->free_list);
-				spin_unlock(&vbq->lock);
+		if (i < 0) {
+			if (vb->free + vb->dirty == VMAP_BBMAP_BITS) {
+				/* fragmented and no outstanding allocations */
+				BUG_ON(vb->dirty != VMAP_BBMAP_BITS);
+				purge = 1;
 			}
-			spin_unlock(&vb->lock);
-			break;
+			goto next;
 		}
+		addr = vb->va->va_start + (i << PAGE_SHIFT);
+		BUG_ON(addr_to_vb_idx(addr) !=
+				addr_to_vb_idx(vb->va->va_start));
+		vb->free -= 1UL << order;
+		if (vb->free == 0) {
+			spin_lock(&vbq->lock);
+			list_del_rcu(&vb->free_list);
+			spin_unlock(&vbq->lock);
+		}
+		spin_unlock(&vb->lock);
+		break;
+next:
 		spin_unlock(&vb->lock);
 	}
+
+	if (purge)
+		purge_fragmented_blocks_thiscpu();
+
 	put_cpu_var(vmap_block_queue);
 	rcu_read_unlock();
 
@@ -860,11 +924,11 @@ static void vb_free(const void *addr, un
 	BUG_ON(!vb);
 
 	spin_lock(&vb->lock);
-	bitmap_allocate_region(vb->dirty_map, offset >> PAGE_SHIFT, order);
+	BUG_ON(bitmap_allocate_region(vb->dirty_map, offset >> PAGE_SHIFT, order));
 
 	vb->dirty += 1UL << order;
 	if (vb->dirty == VMAP_BBMAP_BITS) {
-		BUG_ON(vb->free || !list_empty(&vb->free_list));
+		BUG_ON(vb->free);
 		spin_unlock(&vb->lock);
 		free_vmap_block(vb);
 	} else
@@ -1033,8 +1097,6 @@ void __init vmalloc_init(void)
 		vbq = &per_cpu(vmap_block_queue, i);
 		spin_lock_init(&vbq->lock);
 		INIT_LIST_HEAD(&vbq->free);
-		INIT_LIST_HEAD(&vbq->dirty);
-		vbq->nr_dirty = 0;
 	}
 
 	/* Import existing vmlist entries. */

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Re: [patch 2/2] xfs: use scalable vmap API

[Christoph Hellwig]

On Mon, Jan 25, 2010 at 11:37:46PM +1100, Nick Piggin wrote:
> On Mon, Jan 25, 2010 at 07:33:09PM +1100, Nick Piggin wrote:
> > > Any easy way to get them?  Sorry, not uptodate on your new vmalloc
> > > implementation anymore.
> > 
> > Let me try writing a few (tested) patches here first that I can send you.
> 
> Well is it easy to reproduce the vmap failure? Here is a better tested
> patch if you can try it. It fixes a couple of bugs and does some purging
> of fragmented blocks.
> 
> If it does not help, can you tell me how many CPUs in your system?

The simplest one to reproduce it is a 1 cpu kvm virtual machine.  Will
give your patch a try ASAP - while it's easy to reproduce it takes some
time as I appears only when doing a second xfstests run after a first
finished fine, which makes it look like a leak to me.

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Re: [patch 2/2] xfs: use scalable vmap API

[Christoph Hellwig]

On Mon, Jan 25, 2010 at 11:37:46PM +1100, Nick Piggin wrote:
> On Mon, Jan 25, 2010 at 07:33:09PM +1100, Nick Piggin wrote:
> > > Any easy way to get them?  Sorry, not uptodate on your new vmalloc
> > > implementation anymore.
> > 
> > Let me try writing a few (tested) patches here first that I can send you.
> 
> Well is it easy to reproduce the vmap failure? Here is a better tested
> patch if you can try it. It fixes a couple of bugs and does some purging
> of fragmented blocks.

So far I've not run out of vmalloc space yet with quite a few xfstests
iterations and not encountered any other problems either.

Thanks for looking into this!

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Re: [patch 2/2] xfs: use scalable vmap API

[Nick Piggin]

On Mon, Jan 25, 2010 at 04:34:03PM -0500, Christoph Hellwig wrote:
> On Mon, Jan 25, 2010 at 11:37:46PM +1100, Nick Piggin wrote:
> > On Mon, Jan 25, 2010 at 07:33:09PM +1100, Nick Piggin wrote:
> > > > Any easy way to get them?  Sorry, not uptodate on your new vmalloc
> > > > implementation anymore.
> > > 
> > > Let me try writing a few (tested) patches here first that I can send you.
> > 
> > Well is it easy to reproduce the vmap failure? Here is a better tested
> > patch if you can try it. It fixes a couple of bugs and does some purging
> > of fragmented blocks.
> 
> So far I've not run out of vmalloc space yet with quite a few xfstests
> iterations and not encountered any other problems either.
> 
> Thanks for looking into this!

OK thanks for testing. I'll send it upstream if you haven't had any
problems so far.

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Re: [patch 2/2] xfs: use scalable vmap API

[Christoph Hellwig]

On Wed, Jan 27, 2010 at 07:38:19PM +1100, Nick Piggin wrote:
> > So far I've not run out of vmalloc space yet with quite a few xfstests
> > iterations and not encountered any other problems either.
> > 
> > Thanks for looking into this!
> 
> OK thanks for testing. I'll send it upstream if you haven't had any
> problems so far.

Still working fine, so please send it upstream ASAP.  That'll make
re-eabling the scalable vmap API in XFS much more easier for 2.6.34.

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Re: [patch 2/2] xfs: use scalable vmap API

[Nick Piggin]

On Mon, Feb 01, 2010 at 06:01:54AM -0500, Christoph Hellwig wrote:
> On Wed, Jan 27, 2010 at 07:38:19PM +1100, Nick Piggin wrote:
> > > So far I've not run out of vmalloc space yet with quite a few xfstests
> > > iterations and not encountered any other problems either.
> > > 
> > > Thanks for looking into this!
> > 
> > OK thanks for testing. I'll send it upstream if you haven't had any
> > problems so far.
> 
> Still working fine, so please send it upstream ASAP.  That'll make
> re-eabling the scalable vmap API in XFS much more easier for 2.6.34.

Done. Thanks for testing this.

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Re: [patch 2/2] xfs: use scalable vmap API

[Nick Piggin]

On Mon, Jan 25, 2010 at 06:54:45PM +1100, Nick Piggin wrote:
> When the vmap allocation fails, it would be good to basically see the
> alloc_map and dirty_map for each of the vmap_blocks. This is going to be
> a lot of information. Basically for all blocks with
> free+dirty == VMAP_BBMAP_BITS are ones that could be released and you
> could try the alloc again.

Something like this (untested) is what I'm thinking of. I'll try the XFS
patch again and get something testable over here.

There are RCU bugs in the vmap block list I noticed too which I will
split out and submit seperately.
--
Index: linux-2.6/mm/vmalloc.c
===================================================================
--- linux-2.6.orig/mm/vmalloc.c
+++ linux-2.6/mm/vmalloc.c
@@ -509,6 +509,9 @@ static unsigned long lazy_max_pages(void
 
 static atomic_t vmap_lazy_nr = ATOMIC_INIT(0);
 
+/* for per-CPU blocks */
+static void purge_fragmented_blocks(void);
+
 /*
  * Purges all lazily-freed vmap areas.
  *
@@ -539,6 +542,8 @@ static void __purge_vmap_area_lazy(unsig
 	} else
 		spin_lock(&purge_lock);
 
+	purge_fragmented_blocks();
+
 	rcu_read_lock();
 	list_for_each_entry_rcu(va, &vmap_area_list, list) {
 		if (va->flags & VM_LAZY_FREE) {
@@ -669,8 +674,6 @@ static bool vmap_initialized __read_most
 struct vmap_block_queue {
 	spinlock_t lock;
 	struct list_head free;
-	struct list_head dirty;
-	unsigned int nr_dirty;
 };
 
 struct vmap_block {
@@ -680,10 +683,9 @@ struct vmap_block {
 	unsigned long free, dirty;
 	DECLARE_BITMAP(alloc_map, VMAP_BBMAP_BITS);
 	DECLARE_BITMAP(dirty_map, VMAP_BBMAP_BITS);
-	union {
-		struct list_head free_list;
-		struct rcu_head rcu_head;
-	};
+	struct list_head free_list;
+	struct rcu_head rcu_head;
+	struct list_head purge;
 };
 
 /* Queue of free and dirty vmap blocks, for allocation and flushing purposes */
@@ -759,7 +761,7 @@ static struct vmap_block *new_vmap_block
 	vbq = &get_cpu_var(vmap_block_queue);
 	vb->vbq = vbq;
 	spin_lock(&vbq->lock);
-	list_add(&vb->free_list, &vbq->free);
+	list_add_rcu(&vb->free_list, &vbq->free);
 	spin_unlock(&vbq->lock);
 	put_cpu_var(vmap_block_queue);
 
@@ -808,23 +810,27 @@ again:
 		int i;
 
 		spin_lock(&vb->lock);
+		if (vb->free < 1UL << order)
+			goto next;
+
 		i = bitmap_find_free_region(vb->alloc_map,
 						VMAP_BBMAP_BITS, order);
 
-		if (i >= 0) {
-			addr = vb->va->va_start + (i << PAGE_SHIFT);
-			BUG_ON(addr_to_vb_idx(addr) !=
-					addr_to_vb_idx(vb->va->va_start));
-			vb->free -= 1UL << order;
-			if (vb->free == 0) {
-				spin_lock(&vbq->lock);
-				list_del_init(&vb->free_list);
-				spin_unlock(&vbq->lock);
-			}
-			spin_unlock(&vb->lock);
-			break;
+		if (i < 0)
+			goto next;
+		addr = vb->va->va_start + (i << PAGE_SHIFT);
+		BUG_ON(addr_to_vb_idx(addr) !=
+				addr_to_vb_idx(vb->va->va_start));
+		vb->free -= 1UL << order;
+		if (vb->free == 0) {
+			spin_lock(&vbq->lock);
+			list_del_rcu(&vb->free_list);
+			spin_unlock(&vbq->lock);
 		}
 		spin_unlock(&vb->lock);
+		break;
+next:
+		spin_unlock(&vb->lock);
 	}
 	put_cpu_var(vmap_block_queue);
 	rcu_read_unlock();
@@ -873,6 +879,43 @@ static void vb_free(const void *addr, un
 		spin_unlock(&vb->lock);
 }
 
+static void purge_fragmented_blocks(void)
+{
+	LIST_HEAD(purge);
+	int cpu;
+	struct vmap_block *vb;
+	struct vmap_block *n_vb;
+
+	for_each_possible_cpu(cpu) {
+		struct vmap_block_queue *vbq = &per_cpu(vmap_block_queue, cpu);
+
+		rcu_read_lock();
+		list_for_each_entry_rcu(vb, &vbq->free, free_list) {
+
+			if (vb->free + vb->dirty != VMAP_BBMAP_BITS && vb->dirty != VMAP_BBMAP_BITS)
+				continue;
+
+			spin_lock(&vb->lock);
+			if (vb->free + vb->dirty == VMAP_BBMAP_BITS && vb->dirty != VMAP_BBMAP_BITS) {
+				vb->free = 0; /* prevent further allocs after releasing lock */
+				vb->dirty = VMAP_BBMAP_BITS; /* prevent purging it again */
+				spin_lock(&vbq->lock);
+				list_del_rcu(&vb->free_list);
+				spin_unlock(&vbq->lock);
+				spin_unlock(&vb->lock);
+				list_add_tail(&vb->purge, &purge);
+			} else
+				spin_unlock(&vb->lock);
+		}
+		rcu_read_unlock();
+	}
+
+	list_for_each_entry_safe(vb, n_vb, &purge, purge) {
+		list_del(&vb->purge);
+		free_vmap_block(vb);
+	}
+}
+
 /**
  * vm_unmap_aliases - unmap outstanding lazy aliases in the vmap layer
  *
@@ -1035,8 +1078,6 @@ void __init vmalloc_init(void)
 		vbq = &per_cpu(vmap_block_queue, i);
 		spin_lock_init(&vbq->lock);
 		INIT_LIST_HEAD(&vbq->free);
-		INIT_LIST_HEAD(&vbq->dirty);
-		vbq->nr_dirty = 0;
 	}
 
 	/* Import existing vmlist entries. */

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