[PATCH 0/3] hugetlb: V2 constrain allocation/free based on task mempolicy

[PATCH 0/3] hugetlb: V2 constrain allocation/free based on task mempolicy

[Lee Schermerhorn]

PATCH 0/3 hugetlb: constrain allocation/free based on task mempolicy

Against:  25jun09 mmotm atop the "hugetlb:  balance freeing..."
series

This is V2 of a series of patches to constrain the allocation and
freeing of persistent huge pages using the task NUMA mempolicy of
the task modifying "nr_hugepages".  This series is based on Mel
Gorman's suggestion to use task mempolicy.

V2 addresses review comments from Mel Gorman and Andrew Morton.
See the patch description of patch 2/3.

I have some concerns about a subtle change in behavior [see patch
2/3 and the updated documentation] and the fact that
this mechanism ignores some of the semantics of the mempolicy
mode [again, see the doc].   However, this method seems to work
fairly well.  And, IMO, the resulting code doesn't look all that
bad.

A couple of limitations in this version:

1) I haven't implemented a boot time parameter to constrain the
   boot time allocation of huge pages.  This can be added if
   anyone feels strongly that it is required.

2) I have not implemented a per node nr_overcommit_hugepages as
   David Rientjes and I discussed earlier.  Again, this can be
   added and specific nodes can be addressed using the mempolicy
   as this series does for allocation and free.  However, after
   some experience with the libhugetlbfs test suite, specifically
   attempting to run the test suite constrained by mempolicy and
   a cpuset, I'm thinking that per node overcommit limits might
   not be such a good idea.  This would require an application
   [or the library] to sum the per node limits over the allowed
   nodes and possibly compare to global limits to determine the
   available resources.  Per cpuset limits might work better.
   This are requires more investigation, but this patch series
   doesn't seem to make things worse than they already are in
   this regard.

[PATCH 1/3] hugetlb: add nodemask arg to huge page alloc, free and surplus adjust fcns

[Lee Schermerhorn]

[PATCH 1/3] hugetlb:  add nodemask arg to huge page alloc, free and surplus adjust fcns

Against: 25jun09 mmotm atop the "hugetlb: balance freeing..." series

In preparation for constraining huge page allocation and freeing by the
controlling task's numa mempolicy, add a "nodes_allowed" nodemask pointer
to the allocate, free and surplus adjustment functions.  For now, pass
NULL to indicate default behavior--i.e., use node_online_map.  A
subsqeuent patch will derive a non-default mask from the controlling 
task's numa mempolicy.

Note the "cleanup" in alloc_bootmem_huge_page(): always advance next nid,
even if allocation succeeds.  I believe that this is correct behavior,
and I'll replace it in the next patch which assumes this behavior.
However, perhaps the current code is correct:  we only want to advance
bootmem huge page allocation to the next node when we've exhausted all
huge pages on the current hstate "next_node_to_alloc".  Any who understands
the rationale for this:  please advise.

Signed-off-by: Lee Schermerhorn <lee.schermerhorn@hp.com>

 mm/hugetlb.c |   51 +++++++++++++++++++++++++++++++--------------------
 1 file changed, 31 insertions(+), 20 deletions(-)

Index: linux-2.6.31-rc1-mmotm-090625-1549/mm/hugetlb.c
===================================================================
--- linux-2.6.31-rc1-mmotm-090625-1549.orig/mm/hugetlb.c	2009-07-07 09:58:13.000000000 -0400
+++ linux-2.6.31-rc1-mmotm-090625-1549/mm/hugetlb.c	2009-07-07 09:58:17.000000000 -0400
@@ -631,17 +631,22 @@ static struct page *alloc_fresh_huge_pag
  * if we just successfully allocated a hugepage so that
  * the next caller gets hugepages on the next node.
  */
-static int hstate_next_node_to_alloc(struct hstate *h)
+static int hstate_next_node_to_alloc(struct hstate *h,
+					nodemask_t *nodes_allowed)
 {
 	int next_nid;
-	next_nid = next_node(h->next_nid_to_alloc, node_online_map);
+
+	if (!nodes_allowed)
+		nodes_allowed = &node_online_map;
+
+	next_nid = next_node(h->next_nid_to_alloc, *nodes_allowed);
 	if (next_nid == MAX_NUMNODES)
-		next_nid = first_node(node_online_map);
+		next_nid = first_node(*nodes_allowed);
 	h->next_nid_to_alloc = next_nid;
 	return next_nid;
 }
 
-static int alloc_fresh_huge_page(struct hstate *h)
+static int alloc_fresh_huge_page(struct hstate *h, nodemask_t *nodes_allowed)
 {
 	struct page *page;
 	int start_nid;
@@ -655,7 +660,7 @@ static int alloc_fresh_huge_page(struct 
 		page = alloc_fresh_huge_page_node(h, next_nid);
 		if (page)
 			ret = 1;
-		next_nid = hstate_next_node_to_alloc(h);
+		next_nid = hstate_next_node_to_alloc(h, nodes_allowed);
 	} while (!page && next_nid != start_nid);
 
 	if (ret)
@@ -670,12 +675,16 @@ static int alloc_fresh_huge_page(struct 
  * helper for free_pool_huge_page() - find next node
  * from which to free a huge page
  */
-static int hstate_next_node_to_free(struct hstate *h)
+static int hstate_next_node_to_free(struct hstate *h, nodemask_t *nodes_allowed)
 {
 	int next_nid;
-	next_nid = next_node(h->next_nid_to_free, node_online_map);
+
+	if (!nodes_allowed)
+		nodes_allowed = &node_online_map;
+
+	next_nid = next_node(h->next_nid_to_free, *nodes_allowed);
 	if (next_nid == MAX_NUMNODES)
-		next_nid = first_node(node_online_map);
+		next_nid = first_node(*nodes_allowed);
 	h->next_nid_to_free = next_nid;
 	return next_nid;
 }
@@ -686,7 +695,8 @@ static int hstate_next_node_to_free(stru
  * balanced over allowed nodes.
  * Called with hugetlb_lock locked.
  */
-static int free_pool_huge_page(struct hstate *h, bool acct_surplus)
+static int free_pool_huge_page(struct hstate *h, nodemask_t *nodes_allowed,
+							 bool acct_surplus)
 {
 	int start_nid;
 	int next_nid;
@@ -715,7 +725,7 @@ static int free_pool_huge_page(struct hs
 			update_and_free_page(h, page);
 			ret = 1;
 		}
-		next_nid = hstate_next_node_to_free(h);
+ 		next_nid = hstate_next_node_to_free(h, nodes_allowed);
 	} while (!ret && next_nid != start_nid);
 
 	return ret;
@@ -917,7 +927,7 @@ static void return_unused_surplus_pages(
 	 * on-line nodes for us and will handle the hstate accounting.
 	 */
 	while (nr_pages--) {
-		if (!free_pool_huge_page(h, 1))
+		if (!free_pool_huge_page(h, NULL, 1))
 			break;
 	}
 }
@@ -1030,6 +1040,7 @@ int __weak alloc_bootmem_huge_page(struc
 				NODE_DATA(h->next_nid_to_alloc),
 				huge_page_size(h), huge_page_size(h), 0);
 
+		hstate_next_node_to_alloc(h, NULL); /* always advance nid */
 		if (addr) {
 			/*
 			 * Use the beginning of the huge page to store the
@@ -1039,7 +1050,6 @@ int __weak alloc_bootmem_huge_page(struc
 			m = addr;
 			goto found;
 		}
-		hstate_next_node_to_alloc(h);
 		nr_nodes--;
 	}
 	return 0;
@@ -1083,7 +1093,7 @@ static void __init hugetlb_hstate_alloc_
 		if (h->order >= MAX_ORDER) {
 			if (!alloc_bootmem_huge_page(h))
 				break;
-		} else if (!alloc_fresh_huge_page(h))
+		} else if (!alloc_fresh_huge_page(h, NULL))
 			break;
 	}
 	h->max_huge_pages = i;
@@ -1158,7 +1168,8 @@ static inline void try_to_free_low(struc
  * balanced by operating on them in a round-robin fashion.
  * Returns 1 if an adjustment was made.
  */
-static int adjust_pool_surplus(struct hstate *h, int delta)
+static int adjust_pool_surplus(struct hstate *h, nodemask_t *nodes_allowed,
+				int delta)
 {
 	int start_nid, next_nid;
 	int ret = 0;
@@ -1174,7 +1185,7 @@ static int adjust_pool_surplus(struct hs
 	do {
 		int nid = next_nid;
 		if (delta < 0)  {
-			next_nid = hstate_next_node_to_alloc(h);
+			next_nid = hstate_next_node_to_alloc(h, nodes_allowed);
 			/*
 			 * To shrink on this node, there must be a surplus page
 			 */
@@ -1182,7 +1193,7 @@ static int adjust_pool_surplus(struct hs
 				continue;
 		}
 		if (delta > 0) {
-			next_nid = hstate_next_node_to_free(h);
+			next_nid = hstate_next_node_to_free(h, nodes_allowed);
 			/*
 			 * Surplus cannot exceed the total number of pages
 			 */
@@ -1221,7 +1232,7 @@ static unsigned long set_max_huge_pages(
 	 */
 	spin_lock(&hugetlb_lock);
 	while (h->surplus_huge_pages && count > persistent_huge_pages(h)) {
-		if (!adjust_pool_surplus(h, -1))
+		if (!adjust_pool_surplus(h, NULL, -1))
 			break;
 	}
 
@@ -1232,7 +1243,7 @@ static unsigned long set_max_huge_pages(
 		 * and reducing the surplus.
 		 */
 		spin_unlock(&hugetlb_lock);
-		ret = alloc_fresh_huge_page(h);
+		ret = alloc_fresh_huge_page(h, NULL);
 		spin_lock(&hugetlb_lock);
 		if (!ret)
 			goto out;
@@ -1258,11 +1269,11 @@ static unsigned long set_max_huge_pages(
 	min_count = max(count, min_count);
 	try_to_free_low(h, min_count);
 	while (min_count < persistent_huge_pages(h)) {
-		if (!free_pool_huge_page(h, 0))
+		if (!free_pool_huge_page(h, NULL, 0))
 			break;
 	}
 	while (count < persistent_huge_pages(h)) {
-		if (!adjust_pool_surplus(h, 1))
+		if (!adjust_pool_surplus(h, NULL, 1))
 			break;
 	}
 out:

Re: [PATCH 1/3] hugetlb: add nodemask arg to huge page alloc, free and surplus adjust fcns

[Mel Gorman]

On Wed, Jul 08, 2009 at 03:24:38PM -0400, Lee Schermerhorn wrote:
> [PATCH 1/3] hugetlb:  add nodemask arg to huge page alloc, free and surplus adjust fcns
> 
> Against: 25jun09 mmotm atop the "hugetlb: balance freeing..." series
> 
> In preparation for constraining huge page allocation and freeing by the
> controlling task's numa mempolicy, add a "nodes_allowed" nodemask pointer
> to the allocate, free and surplus adjustment functions.  For now, pass
> NULL to indicate default behavior--i.e., use node_online_map.  A
> subsqeuent patch will derive a non-default mask from the controlling 
> task's numa mempolicy.
> 
> Note the "cleanup" in alloc_bootmem_huge_page(): always advance next nid,
> even if allocation succeeds.  I believe that this is correct behavior,
> and I'll replace it in the next patch which assumes this behavior.
> However, perhaps the current code is correct:  we only want to advance
> bootmem huge page allocation to the next node when we've exhausted all
> huge pages on the current hstate "next_node_to_alloc".  Any who understands
> the rationale for this:  please advise.
> 

I think we covered this up in V1. What I said at the time was

	I strongly suspect that the same node being used until allocation
	failure instead of round-robin is an oversight and not deliberate
	at all. I can't think of a good reason for boot-allocation to behave
	significantly different to runtime-allocation.

But I looked briefly into it a bit more now. Maybe you could change the
changelog to say the following?

==== CUT HERE ====
Note the "cleanup" in alloc_bootmem_huge_page(): always advance next nid,
even if allocation succeeds.  I believe that this is correct behavior,
and I'll replace it in the next patch which assumes this behavior.
According to Mel Gorman;
	I strongly suspect that the same node being used until allocation
	failure instead of round-robin is an oversight and not deliberate
	at all. It appears to be a side-effect of a fix made way back in
	commit 63b4613c3f0d4b724ba259dc6c201bb68b884e1a ["hugetlb: fix
	hugepage allocation with memoryless nodes"]. Prior to that patch
	it looked like allocations would always round-robin even when
	allocation was successful.
==== CUT HERE ====

> Signed-off-by: Lee Schermerhorn <lee.schermerhorn@hp.com>
> 

Other then the comment "/* always advance nid */" being on the same line
as the code and one minor piece of whitespace damage I point out below,
I can't see any problem with the patch.

Reviewed-by: Mel Gorman <mel@csn.ul.ie>


>  mm/hugetlb.c |   51 +++++++++++++++++++++++++++++++--------------------
>  1 file changed, 31 insertions(+), 20 deletions(-)
> 
> Index: linux-2.6.31-rc1-mmotm-090625-1549/mm/hugetlb.c
> ===================================================================
> --- linux-2.6.31-rc1-mmotm-090625-1549.orig/mm/hugetlb.c	2009-07-07 09:58:13.000000000 -0400
> +++ linux-2.6.31-rc1-mmotm-090625-1549/mm/hugetlb.c	2009-07-07 09:58:17.000000000 -0400
> @@ -631,17 +631,22 @@ static struct page *alloc_fresh_huge_pag
>   * if we just successfully allocated a hugepage so that
>   * the next caller gets hugepages on the next node.
>   */
> -static int hstate_next_node_to_alloc(struct hstate *h)
> +static int hstate_next_node_to_alloc(struct hstate *h,
> +					nodemask_t *nodes_allowed)
>  {
>  	int next_nid;
> -	next_nid = next_node(h->next_nid_to_alloc, node_online_map);
> +
> +	if (!nodes_allowed)
> +		nodes_allowed = &node_online_map;
> +
> +	next_nid = next_node(h->next_nid_to_alloc, *nodes_allowed);
>  	if (next_nid == MAX_NUMNODES)
> -		next_nid = first_node(node_online_map);
> +		next_nid = first_node(*nodes_allowed);
>  	h->next_nid_to_alloc = next_nid;
>  	return next_nid;
>  }
>  
> -static int alloc_fresh_huge_page(struct hstate *h)
> +static int alloc_fresh_huge_page(struct hstate *h, nodemask_t *nodes_allowed)
>  {
>  	struct page *page;
>  	int start_nid;
> @@ -655,7 +660,7 @@ static int alloc_fresh_huge_page(struct 
>  		page = alloc_fresh_huge_page_node(h, next_nid);
>  		if (page)
>  			ret = 1;
> -		next_nid = hstate_next_node_to_alloc(h);
> +		next_nid = hstate_next_node_to_alloc(h, nodes_allowed);
>  	} while (!page && next_nid != start_nid);
>  
>  	if (ret)
> @@ -670,12 +675,16 @@ static int alloc_fresh_huge_page(struct 
>   * helper for free_pool_huge_page() - find next node
>   * from which to free a huge page
>   */
> -static int hstate_next_node_to_free(struct hstate *h)
> +static int hstate_next_node_to_free(struct hstate *h, nodemask_t *nodes_allowed)
>  {
>  	int next_nid;
> -	next_nid = next_node(h->next_nid_to_free, node_online_map);
> +
> +	if (!nodes_allowed)
> +		nodes_allowed = &node_online_map;
> +
> +	next_nid = next_node(h->next_nid_to_free, *nodes_allowed);
>  	if (next_nid == MAX_NUMNODES)
> -		next_nid = first_node(node_online_map);
> +		next_nid = first_node(*nodes_allowed);
>  	h->next_nid_to_free = next_nid;
>  	return next_nid;
>  }
> @@ -686,7 +695,8 @@ static int hstate_next_node_to_free(stru
>   * balanced over allowed nodes.
>   * Called with hugetlb_lock locked.
>   */
> -static int free_pool_huge_page(struct hstate *h, bool acct_surplus)
> +static int free_pool_huge_page(struct hstate *h, nodemask_t *nodes_allowed,
> +							 bool acct_surplus)
>  {
>  	int start_nid;
>  	int next_nid;
> @@ -715,7 +725,7 @@ static int free_pool_huge_page(struct hs
>  			update_and_free_page(h, page);
>  			ret = 1;
>  		}
> -		next_nid = hstate_next_node_to_free(h);
> + 		next_nid = hstate_next_node_to_free(h, nodes_allowed);

There is minor whitespace damage there - specifically space at the
beginning of the line.

>  	} while (!ret && next_nid != start_nid);
>  
>  	return ret;
> @@ -917,7 +927,7 @@ static void return_unused_surplus_pages(
>  	 * on-line nodes for us and will handle the hstate accounting.
>  	 */
>  	while (nr_pages--) {
> -		if (!free_pool_huge_page(h, 1))
> +		if (!free_pool_huge_page(h, NULL, 1))
>  			break;
>  	}
>  }
> @@ -1030,6 +1040,7 @@ int __weak alloc_bootmem_huge_page(struc
>  				NODE_DATA(h->next_nid_to_alloc),
>  				huge_page_size(h), huge_page_size(h), 0);
>  
> +		hstate_next_node_to_alloc(h, NULL); /* always advance nid */
>  		if (addr) {
>  			/*
>  			 * Use the beginning of the huge page to store the
> @@ -1039,7 +1050,6 @@ int __weak alloc_bootmem_huge_page(struc
>  			m = addr;
>  			goto found;
>  		}
> -		hstate_next_node_to_alloc(h);
>  		nr_nodes--;
>  	}
>  	return 0;
> @@ -1083,7 +1093,7 @@ static void __init hugetlb_hstate_alloc_
>  		if (h->order >= MAX_ORDER) {
>  			if (!alloc_bootmem_huge_page(h))
>  				break;
> -		} else if (!alloc_fresh_huge_page(h))
> +		} else if (!alloc_fresh_huge_page(h, NULL))
>  			break;
>  	}
>  	h->max_huge_pages = i;
> @@ -1158,7 +1168,8 @@ static inline void try_to_free_low(struc
>   * balanced by operating on them in a round-robin fashion.
>   * Returns 1 if an adjustment was made.
>   */
> -static int adjust_pool_surplus(struct hstate *h, int delta)
> +static int adjust_pool_surplus(struct hstate *h, nodemask_t *nodes_allowed,
> +				int delta)
>  {
>  	int start_nid, next_nid;
>  	int ret = 0;
> @@ -1174,7 +1185,7 @@ static int adjust_pool_surplus(struct hs
>  	do {
>  		int nid = next_nid;
>  		if (delta < 0)  {
> -			next_nid = hstate_next_node_to_alloc(h);
> +			next_nid = hstate_next_node_to_alloc(h, nodes_allowed);
>  			/*
>  			 * To shrink on this node, there must be a surplus page
>  			 */
> @@ -1182,7 +1193,7 @@ static int adjust_pool_surplus(struct hs
>  				continue;
>  		}
>  		if (delta > 0) {
> -			next_nid = hstate_next_node_to_free(h);
> +			next_nid = hstate_next_node_to_free(h, nodes_allowed);
>  			/*
>  			 * Surplus cannot exceed the total number of pages
>  			 */
> @@ -1221,7 +1232,7 @@ static unsigned long set_max_huge_pages(
>  	 */
>  	spin_lock(&hugetlb_lock);
>  	while (h->surplus_huge_pages && count > persistent_huge_pages(h)) {
> -		if (!adjust_pool_surplus(h, -1))
> +		if (!adjust_pool_surplus(h, NULL, -1))
>  			break;
>  	}
>  
> @@ -1232,7 +1243,7 @@ static unsigned long set_max_huge_pages(
>  		 * and reducing the surplus.
>  		 */
>  		spin_unlock(&hugetlb_lock);
> -		ret = alloc_fresh_huge_page(h);
> +		ret = alloc_fresh_huge_page(h, NULL);
>  		spin_lock(&hugetlb_lock);
>  		if (!ret)
>  			goto out;
> @@ -1258,11 +1269,11 @@ static unsigned long set_max_huge_pages(
>  	min_count = max(count, min_count);
>  	try_to_free_low(h, min_count);
>  	while (min_count < persistent_huge_pages(h)) {
> -		if (!free_pool_huge_page(h, 0))
> +		if (!free_pool_huge_page(h, NULL, 0))
>  			break;
>  	}
>  	while (count < persistent_huge_pages(h)) {
> -		if (!adjust_pool_surplus(h, 1))
> +		if (!adjust_pool_surplus(h, NULL, 1))
>  			break;
>  	}
>  out:
> 

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab

Re: [PATCH 1/3] hugetlb: add nodemask arg to huge page alloc, free and surplus adjust fcns

[Lee Schermerhorn]

On Thu, 2009-07-09 at 09:33 +0100, Mel Gorman wrote:
> On Wed, Jul 08, 2009 at 03:24:38PM -0400, Lee Schermerhorn wrote:
> > [PATCH 1/3] hugetlb:  add nodemask arg to huge page alloc, free and surplus adjust fcns
> > 
> > Against: 25jun09 mmotm atop the "hugetlb: balance freeing..." series
> > 
> > In preparation for constraining huge page allocation and freeing by the
> > controlling task's numa mempolicy, add a "nodes_allowed" nodemask pointer
> > to the allocate, free and surplus adjustment functions.  For now, pass
> > NULL to indicate default behavior--i.e., use node_online_map.  A
> > subsqeuent patch will derive a non-default mask from the controlling 
> > task's numa mempolicy.
> > 
> > Note the "cleanup" in alloc_bootmem_huge_page(): always advance next nid,
> > even if allocation succeeds.  I believe that this is correct behavior,
> > and I'll replace it in the next patch which assumes this behavior.
> > However, perhaps the current code is correct:  we only want to advance
> > bootmem huge page allocation to the next node when we've exhausted all
> > huge pages on the current hstate "next_node_to_alloc".  Any who understands
> > the rationale for this:  please advise.
> > 
> 
> I think we covered this up in V1. What I said at the time was
> 
> 	I strongly suspect that the same node being used until allocation
> 	failure instead of round-robin is an oversight and not deliberate
> 	at all. I can't think of a good reason for boot-allocation to behave
> 	significantly different to runtime-allocation.
> 
> But I looked briefly into it a bit more now. Maybe you could change the
> changelog to say the following?
> 
> ==== CUT HERE ====
> Note the "cleanup" in alloc_bootmem_huge_page(): always advance next nid,
> even if allocation succeeds.  I believe that this is correct behavior,
> and I'll replace it in the next patch which assumes this behavior.
> According to Mel Gorman;
> 	I strongly suspect that the same node being used until allocation
> 	failure instead of round-robin is an oversight and not deliberate
> 	at all. It appears to be a side-effect of a fix made way back in
> 	commit 63b4613c3f0d4b724ba259dc6c201bb68b884e1a ["hugetlb: fix
> 	hugepage allocation with memoryless nodes"]. Prior to that patch
> 	it looked like allocations would always round-robin even when
> 	allocation was successful.
> ==== CUT HERE ====

Yes.  Sorry.  Missed updating the description here.  Will resend.

Lee
> 
> > Signed-off-by: Lee Schermerhorn <lee.schermerhorn@hp.com>
> > 
> 
> Other then the comment "/* always advance nid */" being on the same line
> as the code and one minor piece of whitespace damage I point out below,
> I can't see any problem with the patch.
> 
> Reviewed-by: Mel Gorman <mel@csn.ul.ie>
> 
> 
> >  mm/hugetlb.c |   51 +++++++++++++++++++++++++++++++--------------------
> >  1 file changed, 31 insertions(+), 20 deletions(-)
> > 
> > Index: linux-2.6.31-rc1-mmotm-090625-1549/mm/hugetlb.c
> > ===================================================================
> > --- linux-2.6.31-rc1-mmotm-090625-1549.orig/mm/hugetlb.c	2009-07-07 09:58:13.000000000 -0400
> > +++ linux-2.6.31-rc1-mmotm-090625-1549/mm/hugetlb.c	2009-07-07 09:58:17.000000000 -0400
> > @@ -631,17 +631,22 @@ static struct page *alloc_fresh_huge_pag
> >   * if we just successfully allocated a hugepage so that
> >   * the next caller gets hugepages on the next node.
> >   */
> > -static int hstate_next_node_to_alloc(struct hstate *h)
> > +static int hstate_next_node_to_alloc(struct hstate *h,
> > +					nodemask_t *nodes_allowed)
> >  {
> >  	int next_nid;
> > -	next_nid = next_node(h->next_nid_to_alloc, node_online_map);
> > +
> > +	if (!nodes_allowed)
> > +		nodes_allowed = &node_online_map;
> > +
> > +	next_nid = next_node(h->next_nid_to_alloc, *nodes_allowed);
> >  	if (next_nid == MAX_NUMNODES)
> > -		next_nid = first_node(node_online_map);
> > +		next_nid = first_node(*nodes_allowed);
> >  	h->next_nid_to_alloc = next_nid;
> >  	return next_nid;
> >  }
> >  
> > -static int alloc_fresh_huge_page(struct hstate *h)
> > +static int alloc_fresh_huge_page(struct hstate *h, nodemask_t *nodes_allowed)
> >  {
> >  	struct page *page;
> >  	int start_nid;
> > @@ -655,7 +660,7 @@ static int alloc_fresh_huge_page(struct 
> >  		page = alloc_fresh_huge_page_node(h, next_nid);
> >  		if (page)
> >  			ret = 1;
> > -		next_nid = hstate_next_node_to_alloc(h);
> > +		next_nid = hstate_next_node_to_alloc(h, nodes_allowed);
> >  	} while (!page && next_nid != start_nid);
> >  
> >  	if (ret)
> > @@ -670,12 +675,16 @@ static int alloc_fresh_huge_page(struct 
> >   * helper for free_pool_huge_page() - find next node
> >   * from which to free a huge page
> >   */
> > -static int hstate_next_node_to_free(struct hstate *h)
> > +static int hstate_next_node_to_free(struct hstate *h, nodemask_t *nodes_allowed)
> >  {
> >  	int next_nid;
> > -	next_nid = next_node(h->next_nid_to_free, node_online_map);
> > +
> > +	if (!nodes_allowed)
> > +		nodes_allowed = &node_online_map;
> > +
> > +	next_nid = next_node(h->next_nid_to_free, *nodes_allowed);
> >  	if (next_nid == MAX_NUMNODES)
> > -		next_nid = first_node(node_online_map);
> > +		next_nid = first_node(*nodes_allowed);
> >  	h->next_nid_to_free = next_nid;
> >  	return next_nid;
> >  }
> > @@ -686,7 +695,8 @@ static int hstate_next_node_to_free(stru
> >   * balanced over allowed nodes.
> >   * Called with hugetlb_lock locked.
> >   */
> > -static int free_pool_huge_page(struct hstate *h, bool acct_surplus)
> > +static int free_pool_huge_page(struct hstate *h, nodemask_t *nodes_allowed,
> > +							 bool acct_surplus)
> >  {
> >  	int start_nid;
> >  	int next_nid;
> > @@ -715,7 +725,7 @@ static int free_pool_huge_page(struct hs
> >  			update_and_free_page(h, page);
> >  			ret = 1;
> >  		}
> > -		next_nid = hstate_next_node_to_free(h);
> > + 		next_nid = hstate_next_node_to_free(h, nodes_allowed);
> 
> There is minor whitespace damage there - specifically space at the
> beginning of the line.

Hmmm, I probably botched a patch rejection fix up...

Thanks.

> 
> >  	} while (!ret && next_nid != start_nid);
> >  
> >  	return ret;
> > @@ -917,7 +927,7 @@ static void return_unused_surplus_pages(
> >  	 * on-line nodes for us and will handle the hstate accounting.
> >  	 */
> >  	while (nr_pages--) {
> > -		if (!free_pool_huge_page(h, 1))
> > +		if (!free_pool_huge_page(h, NULL, 1))
> >  			break;
> >  	}
> >  }
> > @@ -1030,6 +1040,7 @@ int __weak alloc_bootmem_huge_page(struc
> >  				NODE_DATA(h->next_nid_to_alloc),
> >  				huge_page_size(h), huge_page_size(h), 0);
> >  
> > +		hstate_next_node_to_alloc(h, NULL); /* always advance nid */
> >  		if (addr) {
> >  			/*
> >  			 * Use the beginning of the huge page to store the
> > @@ -1039,7 +1050,6 @@ int __weak alloc_bootmem_huge_page(struc
> >  			m = addr;
> >  			goto found;
> >  		}
> > -		hstate_next_node_to_alloc(h);
> >  		nr_nodes--;
> >  	}
> >  	return 0;
> > @@ -1083,7 +1093,7 @@ static void __init hugetlb_hstate_alloc_
> >  		if (h->order >= MAX_ORDER) {
> >  			if (!alloc_bootmem_huge_page(h))
> >  				break;
> > -		} else if (!alloc_fresh_huge_page(h))
> > +		} else if (!alloc_fresh_huge_page(h, NULL))
> >  			break;
> >  	}
> >  	h->max_huge_pages = i;
> > @@ -1158,7 +1168,8 @@ static inline void try_to_free_low(struc
> >   * balanced by operating on them in a round-robin fashion.
> >   * Returns 1 if an adjustment was made.
> >   */
> > -static int adjust_pool_surplus(struct hstate *h, int delta)
> > +static int adjust_pool_surplus(struct hstate *h, nodemask_t *nodes_allowed,
> > +				int delta)
> >  {
> >  	int start_nid, next_nid;
> >  	int ret = 0;
> > @@ -1174,7 +1185,7 @@ static int adjust_pool_surplus(struct hs
> >  	do {
> >  		int nid = next_nid;
> >  		if (delta < 0)  {
> > -			next_nid = hstate_next_node_to_alloc(h);
> > +			next_nid = hstate_next_node_to_alloc(h, nodes_allowed);
> >  			/*
> >  			 * To shrink on this node, there must be a surplus page
> >  			 */
> > @@ -1182,7 +1193,7 @@ static int adjust_pool_surplus(struct hs
> >  				continue;
> >  		}
> >  		if (delta > 0) {
> > -			next_nid = hstate_next_node_to_free(h);
> > +			next_nid = hstate_next_node_to_free(h, nodes_allowed);
> >  			/*
> >  			 * Surplus cannot exceed the total number of pages
> >  			 */
> > @@ -1221,7 +1232,7 @@ static unsigned long set_max_huge_pages(
> >  	 */
> >  	spin_lock(&hugetlb_lock);
> >  	while (h->surplus_huge_pages && count > persistent_huge_pages(h)) {
> > -		if (!adjust_pool_surplus(h, -1))
> > +		if (!adjust_pool_surplus(h, NULL, -1))
> >  			break;
> >  	}
> >  
> > @@ -1232,7 +1243,7 @@ static unsigned long set_max_huge_pages(
> >  		 * and reducing the surplus.
> >  		 */
> >  		spin_unlock(&hugetlb_lock);
> > -		ret = alloc_fresh_huge_page(h);
> > +		ret = alloc_fresh_huge_page(h, NULL);
> >  		spin_lock(&hugetlb_lock);
> >  		if (!ret)
> >  			goto out;
> > @@ -1258,11 +1269,11 @@ static unsigned long set_max_huge_pages(
> >  	min_count = max(count, min_count);
> >  	try_to_free_low(h, min_count);
> >  	while (min_count < persistent_huge_pages(h)) {
> > -		if (!free_pool_huge_page(h, 0))
> > +		if (!free_pool_huge_page(h, NULL, 0))
> >  			break;
> >  	}
> >  	while (count < persistent_huge_pages(h)) {
> > -		if (!adjust_pool_surplus(h, 1))
> > +		if (!adjust_pool_surplus(h, NULL, 1))
> >  			break;
> >  	}
> >  out:
> > 
> 

[PATCH 2/3] hugetlb: derive huge pages nodes allowed from task mempolicy

[Lee Schermerhorn]

[PATCH 2/3] hugetlb:  derive huge pages nodes allowed from task mempolicy

Against: 25jun09 mmotm atop the "hugetlb: balance freeing..." series

V2:
+ cleaned up comments, removed some deemed unnecessary,
  add some suggested by review
+ removed check for !current in huge_mpol_nodes_allowed().
+ added 'current->comm' to warning message in huge_mpol_nodes_allowed().
+ added VM_BUG_ON() assertion in hugetlb.c next_node_allowed() to
  catch out of range node id.
+ add examples to patch description

This patch derives a "nodes_allowed" node mask from the numa
mempolicy of the task modifying the number of persistent huge
pages to control the allocation, freeing and adjusting of surplus
huge pages.  This mask is derived as follows:

* For "default" [NULL] task mempolicy, a NULL nodemask_t pointer
  is produced.  This will cause the hugetlb subsystem to use
  node_online_map as the "nodes_allowed".  This preserves the
  behavior before this patch.
* For "preferred" mempolicy, including explicit local allocation,
  a nodemask with the single preferred node will be produced. 
  "local" policy will NOT track any internode migrations of the
  task adjusting nr_hugepages.
* For "bind" and "interleave" policy, the mempolicy's nodemask
  will be used.
* Other than to inform the construction of the nodes_allowed node
  mask, the actual mempolicy mode is ignored.  That is, all modes
  behave like interleave over the resulting nodes_allowed mask
  with no "fallback".

Because we may have allocated or freed a huge page with a 
different policy/nodes_allowed previously, we always need to
check that the next_node_to_{alloc|free} exists in the current
nodes_allowed mask.  To avoid duplication of code, this is done
in the hstate_next_node_to_{alloc|free}() functions.  So,
these functions have been modified to allow them to be called
to obtain the "start_nid".  Then, whereas prior to this patch
we unconditionally called hstate_next_node_to_{alloc|free}(),
whether or not we successfully allocated/freed a huge page on
the node, now we only call these functions on failure to alloc/free.

Notes:

1) This patch introduces a subtle change in behavior:  huge page
   allocation and freeing will be constrained by any mempolicy
   that the task adjusting the huge page pool inherits from its
   parent.  This policy could come from a distant ancestor.  The
   adminstrator adjusting the huge page pool without explicitly
   specifying a mempolicy via numactl might be surprised by this.
   Additionaly, any mempolicy specified by numactl will be
   constrained by the cpuset in which numactl is invoked.

2) Hugepages allocated at boot time use the node_online_map.
   An additional patch could implement a temporary boot time
   huge pages nodes_allowed command line parameter.

3) Using mempolicy to control persistent huge page allocation
   and freeing requires no change to hugeadm when invoking
   it via numactl, as shown in the examples below.  However,
   hugeadm could be enhanced to take the allowed nodes as an
   argument and set its task mempolicy itself.  This would allow
   it to detect and warn about any non-default mempolicy that it
   inherited from its parent, thus alleviating the issue described
   in Note 1 above.

See the updated documentation [next patch] for more information
about the implications of this patch.

Examples:

Starting with:

	Node 0 HugePages_Total:     0
	Node 1 HugePages_Total:     0
	Node 2 HugePages_Total:     0
	Node 3 HugePages_Total:     0

Default behavior [with or without this patch] balances persistent
hugepage allocation across nodes [with sufficient contiguous memory]:

	hugeadm --pool-pages-min=2048Kb:32

yields:

	Node 0 HugePages_Total:     8
	Node 1 HugePages_Total:     8
	Node 2 HugePages_Total:     8
	Node 3 HugePages_Total:     8

Applying mempolicy--e.g., with numactl [using '-m' a.k.a.
'--membind' because it allows multiple nodes to be specified
and it's easy to type]--we can allocate huge pages on
individual nodes or sets of nodes.  So, starting from the 
condition above, with 8 huge pages per node:

	numactl -m 2 hugeadm --pool-pages-min=2048Kb:+8

yields:

	Node 0 HugePages_Total:     8
	Node 1 HugePages_Total:     8
	Node 2 HugePages_Total:    16
	Node 3 HugePages_Total:     8

The incremental 8 huge pages were restricted to node 2 by the
specified mempolicy.

Similarly, we can use mempolicy to free persistent huge pages
from specified nodes:

	numactl -m 0,1 hugeadm --pool-pages-min=2048Kb:-8

yields:

	Node 0 HugePages_Total:     4
	Node 1 HugePages_Total:     4
	Node 2 HugePages_Total:    16
	Node 3 HugePages_Total:     8

The 8 huge pages freed were balanced over nodes 0 and 1.

Signed-off-by: Lee Schermerhorn <lee.schermerhorn@hp.com>

 include/linux/mempolicy.h |    3 +
 mm/hugetlb.c              |  101 +++++++++++++++++++++++++++++++---------------
 mm/mempolicy.c            |   61 +++++++++++++++++++++++++++
 3 files changed, 133 insertions(+), 32 deletions(-)

Index: linux-2.6.31-rc1-mmotm-090625-1549/mm/hugetlb.c
===================================================================
--- linux-2.6.31-rc1-mmotm-090625-1549.orig/mm/hugetlb.c	2009-07-07 09:58:17.000000000 -0400
+++ linux-2.6.31-rc1-mmotm-090625-1549/mm/hugetlb.c	2009-07-07 13:25:41.000000000 -0400
@@ -621,29 +621,54 @@ static struct page *alloc_fresh_huge_pag
 }
 
 /*
+ * common helper functions for hstate_next_node_to_{alloc|free}.
+ * We may have allocated or freed a huge pages based on a different
+ * nodes_allowed, previously, so h->next_node_to_{alloc|free} might
+ * be outside of *nodes_allowed.  Ensure that we use the next
+ * allowed node for alloc or free.
+ */
+static int next_node_allowed(int nid, nodemask_t *nodes_allowed)
+{
+	nid = next_node(nid, *nodes_allowed);
+	if (nid == MAX_NUMNODES)
+		nid = first_node(*nodes_allowed);
+	VM_BUG_ON(nid >= MAX_NUMNODES);
+
+	return nid;
+}
+
+static int this_node_allowed(int nid, nodemask_t *nodes_allowed)
+{
+	if (!node_isset(nid, *nodes_allowed))
+		nid = next_node_allowed(nid, nodes_allowed);
+	return nid;
+}
+
+/*
  * Use a helper variable to find the next node and then
  * copy it back to next_nid_to_alloc afterwards:
  * otherwise there's a window in which a racer might
  * pass invalid nid MAX_NUMNODES to alloc_pages_exact_node.
  * But we don't need to use a spin_lock here: it really
  * doesn't matter if occasionally a racer chooses the
- * same nid as we do.  Move nid forward in the mask even
- * if we just successfully allocated a hugepage so that
- * the next caller gets hugepages on the next node.
+ * same nid as we do.  Move nid forward in the mask whether
+ * or not we just successfully allocated a hugepage so that
+ * the next allocation addresses the next node.
  */
 static int hstate_next_node_to_alloc(struct hstate *h,
 					nodemask_t *nodes_allowed)
 {
-	int next_nid;
+	int nid, next_nid;
 
 	if (!nodes_allowed)
 		nodes_allowed = &node_online_map;
 
-	next_nid = next_node(h->next_nid_to_alloc, *nodes_allowed);
-	if (next_nid == MAX_NUMNODES)
-		next_nid = first_node(*nodes_allowed);
+	nid = this_node_allowed(h->next_nid_to_alloc, nodes_allowed);
+
+	next_nid = next_node_allowed(nid, nodes_allowed);
 	h->next_nid_to_alloc = next_nid;
-	return next_nid;
+
+	return nid;
 }
 
 static int alloc_fresh_huge_page(struct hstate *h, nodemask_t *nodes_allowed)
@@ -653,15 +678,17 @@ static int alloc_fresh_huge_page(struct 
 	int next_nid;
 	int ret = 0;
 
-	start_nid = h->next_nid_to_alloc;
+	start_nid = hstate_next_node_to_alloc(h, nodes_allowed);
 	next_nid = start_nid;
 
 	do {
 		page = alloc_fresh_huge_page_node(h, next_nid);
-		if (page)
+		if (page) {
 			ret = 1;
+			break;
+		}
 		next_nid = hstate_next_node_to_alloc(h, nodes_allowed);
-	} while (!page && next_nid != start_nid);
+	} while (next_nid != start_nid);
 
 	if (ret)
 		count_vm_event(HTLB_BUDDY_PGALLOC);
@@ -672,21 +699,23 @@ static int alloc_fresh_huge_page(struct 
 }
 
 /*
- * helper for free_pool_huge_page() - find next node
- * from which to free a huge page
+ * helper for free_pool_huge_page() - return the next node
+ * from which to free a huge page.  Advance the next node id
+ * whether or not we find a free huge page to free so that the
+ * next attempt to free addresses the next node.
  */
 static int hstate_next_node_to_free(struct hstate *h, nodemask_t *nodes_allowed)
 {
-	int next_nid;
+	int nid, next_nid;
 
 	if (!nodes_allowed)
 		nodes_allowed = &node_online_map;
 
-	next_nid = next_node(h->next_nid_to_free, *nodes_allowed);
-	if (next_nid == MAX_NUMNODES)
-		next_nid = first_node(*nodes_allowed);
+	nid = this_node_allowed(h->next_nid_to_free, nodes_allowed);
+	next_nid = next_node_allowed(nid, nodes_allowed);
 	h->next_nid_to_free = next_nid;
-	return next_nid;
+
+	return nid;
 }
 
 /*
@@ -702,7 +731,7 @@ static int free_pool_huge_page(struct hs
 	int next_nid;
 	int ret = 0;
 
-	start_nid = h->next_nid_to_free;
+	start_nid = hstate_next_node_to_free(h, nodes_allowed);
 	next_nid = start_nid;
 
 	do {
@@ -724,9 +753,10 @@ static int free_pool_huge_page(struct hs
 			}
 			update_and_free_page(h, page);
 			ret = 1;
+			break;
 		}
  		next_nid = hstate_next_node_to_free(h, nodes_allowed);
-	} while (!ret && next_nid != start_nid);
+	} while (next_nid != start_nid);
 
 	return ret;
 }
@@ -1037,10 +1067,9 @@ int __weak alloc_bootmem_huge_page(struc
 		void *addr;
 
 		addr = __alloc_bootmem_node_nopanic(
-				NODE_DATA(h->next_nid_to_alloc),
+				NODE_DATA(hstate_next_node_to_alloc(h, NULL)),
 				huge_page_size(h), huge_page_size(h), 0);
 
-		hstate_next_node_to_alloc(h, NULL); /* always advance nid */
 		if (addr) {
 			/*
 			 * Use the beginning of the huge page to store the
@@ -1177,29 +1206,33 @@ static int adjust_pool_surplus(struct hs
 	VM_BUG_ON(delta != -1 && delta != 1);
 
 	if (delta < 0)
-		start_nid = h->next_nid_to_alloc;
+		start_nid = hstate_next_node_to_alloc(h, nodes_allowed);
 	else
-		start_nid = h->next_nid_to_free;
+		start_nid = hstate_next_node_to_free(h, nodes_allowed);
 	next_nid = start_nid;
 
 	do {
 		int nid = next_nid;
 		if (delta < 0)  {
-			next_nid = hstate_next_node_to_alloc(h, nodes_allowed);
 			/*
 			 * To shrink on this node, there must be a surplus page
 			 */
-			if (!h->surplus_huge_pages_node[nid])
+			if (!h->surplus_huge_pages_node[nid]) {
+				next_nid = hstate_next_node_to_alloc(h,
+								nodes_allowed);
 				continue;
+			}
 		}
 		if (delta > 0) {
-			next_nid = hstate_next_node_to_free(h, nodes_allowed);
 			/*
 			 * Surplus cannot exceed the total number of pages
 			 */
 			if (h->surplus_huge_pages_node[nid] >=
-						h->nr_huge_pages_node[nid])
+						h->nr_huge_pages_node[nid]) {
+				next_nid = hstate_next_node_to_free(h,
+								nodes_allowed);
 				continue;
+			}
 		}
 
 		h->surplus_huge_pages += delta;
@@ -1215,10 +1248,13 @@ static int adjust_pool_surplus(struct hs
 static unsigned long set_max_huge_pages(struct hstate *h, unsigned long count)
 {
 	unsigned long min_count, ret;
+	nodemask_t *nodes_allowed;
 
 	if (h->order >= MAX_ORDER)
 		return h->max_huge_pages;
 
+	nodes_allowed = huge_mpol_nodes_allowed();
+
 	/*
 	 * Increase the pool size
 	 * First take pages out of surplus state.  Then make up the
@@ -1232,7 +1268,7 @@ static unsigned long set_max_huge_pages(
 	 */
 	spin_lock(&hugetlb_lock);
 	while (h->surplus_huge_pages && count > persistent_huge_pages(h)) {
-		if (!adjust_pool_surplus(h, NULL, -1))
+		if (!adjust_pool_surplus(h, nodes_allowed, -1))
 			break;
 	}
 
@@ -1243,7 +1279,7 @@ static unsigned long set_max_huge_pages(
 		 * and reducing the surplus.
 		 */
 		spin_unlock(&hugetlb_lock);
-		ret = alloc_fresh_huge_page(h, NULL);
+		ret = alloc_fresh_huge_page(h, nodes_allowed);
 		spin_lock(&hugetlb_lock);
 		if (!ret)
 			goto out;
@@ -1269,16 +1305,17 @@ static unsigned long set_max_huge_pages(
 	min_count = max(count, min_count);
 	try_to_free_low(h, min_count);
 	while (min_count < persistent_huge_pages(h)) {
-		if (!free_pool_huge_page(h, NULL, 0))
+		if (!free_pool_huge_page(h, nodes_allowed, 0))
 			break;
 	}
 	while (count < persistent_huge_pages(h)) {
-		if (!adjust_pool_surplus(h, NULL, 1))
+		if (!adjust_pool_surplus(h, nodes_allowed, 1))
 			break;
 	}
 out:
 	ret = persistent_huge_pages(h);
 	spin_unlock(&hugetlb_lock);
+	kfree(nodes_allowed);
 	return ret;
 }
 
Index: linux-2.6.31-rc1-mmotm-090625-1549/mm/mempolicy.c
===================================================================
--- linux-2.6.31-rc1-mmotm-090625-1549.orig/mm/mempolicy.c	2009-07-07 09:46:48.000000000 -0400
+++ linux-2.6.31-rc1-mmotm-090625-1549/mm/mempolicy.c	2009-07-07 13:48:06.000000000 -0400
@@ -1544,6 +1544,67 @@ struct zonelist *huge_zonelist(struct vm
 	}
 	return zl;
 }
+
+/*
+ * huge_mpol_nodes_allowed -- mempolicy extension for huge pages.
+ *
+ * Returns a [pointer to a] nodelist based on the current task's mempolicy
+ * to constraing the allocation and freeing of persistent huge pages
+ * 'Preferred', 'local' and 'interleave' mempolicy will behave more like
+ * 'bind' policy in this context.  An attempt to allocate a persistent huge
+ * page will never "fallback" to another node inside the buddy system
+ * allocator.
+ *
+ * If the task's mempolicy is "default" [NULL], just return NULL for
+ * default behavior.  Otherwise, extract the policy nodemask for 'bind'
+ * or 'interleave' policy or construct a nodemask for 'preferred' or
+ * 'local' policy and return a pointer to a kmalloc()ed nodemask_t.
+ *
+ * N.B., it is the caller's responsibility to free a returned nodemask.
+ */
+nodemask_t *huge_mpol_nodes_allowed(void)
+{
+	nodemask_t *nodes_allowed = NULL;
+	struct mempolicy *mempolicy;
+	int nid;
+
+	if (!current->mempolicy)
+		return NULL;
+
+	mpol_get(current->mempolicy);
+	nodes_allowed = kmalloc(sizeof(*nodes_allowed), GFP_KERNEL);
+	if (!nodes_allowed) {
+		printk(KERN_WARNING "%s unable to allocate nodes allowed mask "
+			"for huge page allocation.\nFalling back to default.\n",
+			current->comm);
+		goto out;
+	}
+	nodes_clear(*nodes_allowed);
+
+	mempolicy = current->mempolicy;
+	switch(mempolicy->mode) {
+	case MPOL_PREFERRED:
+		if (mempolicy->flags & MPOL_F_LOCAL)
+			nid = numa_node_id();
+		else
+			nid = mempolicy->v.preferred_node;
+		node_set(nid, *nodes_allowed);
+		break;
+
+	case MPOL_BIND:
+		/* Fall through */
+	case MPOL_INTERLEAVE:
+		*nodes_allowed =  mempolicy->v.nodes;
+		break;
+
+	default:
+		BUG();
+	}
+
+out:
+	mpol_put(current->mempolicy);
+	return nodes_allowed;
+}
 #endif
 
 /* Allocate a page in interleaved policy.
Index: linux-2.6.31-rc1-mmotm-090625-1549/include/linux/mempolicy.h
===================================================================
--- linux-2.6.31-rc1-mmotm-090625-1549.orig/include/linux/mempolicy.h	2009-07-06 13:05:23.000000000 -0400
+++ linux-2.6.31-rc1-mmotm-090625-1549/include/linux/mempolicy.h	2009-07-07 09:58:32.000000000 -0400
@@ -201,6 +201,7 @@ extern void mpol_fix_fork_child_flag(str
 extern struct zonelist *huge_zonelist(struct vm_area_struct *vma,
 				unsigned long addr, gfp_t gfp_flags,
 				struct mempolicy **mpol, nodemask_t **nodemask);
+extern nodemask_t *huge_mpol_nodes_allowed(void);
 extern unsigned slab_node(struct mempolicy *policy);
 
 extern enum zone_type policy_zone;
@@ -328,6 +329,8 @@ static inline struct zonelist *huge_zone
 	return node_zonelist(0, gfp_flags);
 }
 
+static inline nodemask_t *huge_mpol_nodes_allowed(void) { return NULL; }
+
 static inline int do_migrate_pages(struct mm_struct *mm,
 			const nodemask_t *from_nodes,
 			const nodemask_t *to_nodes, int flags)

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Re: [PATCH 2/3] hugetlb: derive huge pages nodes allowed from task mempolicy

[Mel Gorman]

On Wed, Jul 08, 2009 at 03:24:46PM -0400, Lee Schermerhorn wrote:
> [PATCH 2/3] hugetlb:  derive huge pages nodes allowed from task mempolicy
> 
> Against: 25jun09 mmotm atop the "hugetlb: balance freeing..." series
> 
> V2:
> + cleaned up comments, removed some deemed unnecessary,
>   add some suggested by review
> + removed check for !current in huge_mpol_nodes_allowed().
> + added 'current->comm' to warning message in huge_mpol_nodes_allowed().
> + added VM_BUG_ON() assertion in hugetlb.c next_node_allowed() to
>   catch out of range node id.
> + add examples to patch description
> 
> This patch derives a "nodes_allowed" node mask from the numa
> mempolicy of the task modifying the number of persistent huge
> pages to control the allocation, freeing and adjusting of surplus
> huge pages.  This mask is derived as follows:
> 
> * For "default" [NULL] task mempolicy, a NULL nodemask_t pointer
>   is produced.  This will cause the hugetlb subsystem to use
>   node_online_map as the "nodes_allowed".  This preserves the
>   behavior before this patch.
> * For "preferred" mempolicy, including explicit local allocation,
>   a nodemask with the single preferred node will be produced. 
>   "local" policy will NOT track any internode migrations of the
>   task adjusting nr_hugepages.
> * For "bind" and "interleave" policy, the mempolicy's nodemask
>   will be used.
> * Other than to inform the construction of the nodes_allowed node
>   mask, the actual mempolicy mode is ignored.  That is, all modes
>   behave like interleave over the resulting nodes_allowed mask
>   with no "fallback".
> 
> Because we may have allocated or freed a huge page with a 
> different policy/nodes_allowed previously, we always need to
> check that the next_node_to_{alloc|free} exists in the current
> nodes_allowed mask.  To avoid duplication of code, this is done
> in the hstate_next_node_to_{alloc|free}() functions.  So,
> these functions have been modified to allow them to be called
> to obtain the "start_nid".  Then, whereas prior to this patch
> we unconditionally called hstate_next_node_to_{alloc|free}(),
> whether or not we successfully allocated/freed a huge page on
> the node, now we only call these functions on failure to alloc/free.
> 
> Notes:
> 
> 1) This patch introduces a subtle change in behavior:  huge page
>    allocation and freeing will be constrained by any mempolicy
>    that the task adjusting the huge page pool inherits from its
>    parent.  This policy could come from a distant ancestor.  The
>    adminstrator adjusting the huge page pool without explicitly
>    specifying a mempolicy via numactl might be surprised by this.
>    Additionaly, any mempolicy specified by numactl will be
>    constrained by the cpuset in which numactl is invoked.
> 
> 2) Hugepages allocated at boot time use the node_online_map.
>    An additional patch could implement a temporary boot time
>    huge pages nodes_allowed command line parameter.
> 
> 3) Using mempolicy to control persistent huge page allocation
>    and freeing requires no change to hugeadm when invoking
>    it via numactl, as shown in the examples below.  However,
>    hugeadm could be enhanced to take the allowed nodes as an
>    argument and set its task mempolicy itself.  This would allow
>    it to detect and warn about any non-default mempolicy that it
>    inherited from its parent, thus alleviating the issue described
>    in Note 1 above.
> 
> See the updated documentation [next patch] for more information
> about the implications of this patch.
> 
> Examples:
> 
> Starting with:
> 
> 	Node 0 HugePages_Total:     0
> 	Node 1 HugePages_Total:     0
> 	Node 2 HugePages_Total:     0
> 	Node 3 HugePages_Total:     0
> 
> Default behavior [with or without this patch] balances persistent
> hugepage allocation across nodes [with sufficient contiguous memory]:
> 
> 	hugeadm --pool-pages-min=2048Kb:32
> 
> yields:
> 
> 	Node 0 HugePages_Total:     8
> 	Node 1 HugePages_Total:     8
> 	Node 2 HugePages_Total:     8
> 	Node 3 HugePages_Total:     8
> 
> Applying mempolicy--e.g., with numactl [using '-m' a.k.a.
> '--membind' because it allows multiple nodes to be specified
> and it's easy to type]--we can allocate huge pages on
> individual nodes or sets of nodes.  So, starting from the 
> condition above, with 8 huge pages per node:
> 
> 	numactl -m 2 hugeadm --pool-pages-min=2048Kb:+8
> 
> yields:
> 
> 	Node 0 HugePages_Total:     8
> 	Node 1 HugePages_Total:     8
> 	Node 2 HugePages_Total:    16
> 	Node 3 HugePages_Total:     8
> 
> The incremental 8 huge pages were restricted to node 2 by the
> specified mempolicy.
> 
> Similarly, we can use mempolicy to free persistent huge pages
> from specified nodes:
> 
> 	numactl -m 0,1 hugeadm --pool-pages-min=2048Kb:-8
> 
> yields:
> 
> 	Node 0 HugePages_Total:     4
> 	Node 1 HugePages_Total:     4
> 	Node 2 HugePages_Total:    16
> 	Node 3 HugePages_Total:     8
> 
> The 8 huge pages freed were balanced over nodes 0 and 1.
> 
> Signed-off-by: Lee Schermerhorn <lee.schermerhorn@hp.com>
> 

Much better changelog.

Reading through, the main problem I can see is that the reservation
calculations are still not nodemask aware. This means that mmap() can return
successfully and the process that called mmap() get unexpectedly killed
because while there were enough hugepages overall, there were not enough in
the pools allowed by the nodemask. This is a stability problem for those that
create hugepage pools on one set of nodes and run applications on a subset.
Minimally, can this situation be warned about and a note in the documentation
about it?

Testing with it, I couldn't break it as such but libhugetlbfs is showing up
an anomaly with the counters tests. Some investigation showed that it was
because when it shrinks the pool, one page gets accounted for as a surplus
page which was unexpected.

I only got as far as determining the problem was in the patches that free
pages in a round-robin fashion but then ran out of time on the machine. I'll
see can I reproduce using fake-numa on a normal x86-64 instead of a real
NUMA machine but maybe you have a fix for this problem already?

>  include/linux/mempolicy.h |    3 +
>  mm/hugetlb.c              |  101 +++++++++++++++++++++++++++++++---------------
>  mm/mempolicy.c            |   61 +++++++++++++++++++++++++++
>  3 files changed, 133 insertions(+), 32 deletions(-)
> 
> Index: linux-2.6.31-rc1-mmotm-090625-1549/mm/hugetlb.c
> ===================================================================
> --- linux-2.6.31-rc1-mmotm-090625-1549.orig/mm/hugetlb.c	2009-07-07 09:58:17.000000000 -0400
> +++ linux-2.6.31-rc1-mmotm-090625-1549/mm/hugetlb.c	2009-07-07 13:25:41.000000000 -0400
> @@ -621,29 +621,54 @@ static struct page *alloc_fresh_huge_pag
>  }
>  
>  /*
> + * common helper functions for hstate_next_node_to_{alloc|free}.
> + * We may have allocated or freed a huge pages based on a different
> + * nodes_allowed, previously, so h->next_node_to_{alloc|free} might
> + * be outside of *nodes_allowed.  Ensure that we use the next
> + * allowed node for alloc or free.
> + */
> +static int next_node_allowed(int nid, nodemask_t *nodes_allowed)
> +{
> +	nid = next_node(nid, *nodes_allowed);
> +	if (nid == MAX_NUMNODES)
> +		nid = first_node(*nodes_allowed);
> +	VM_BUG_ON(nid >= MAX_NUMNODES);
> +
> +	return nid;
> +}
> +
> +static int this_node_allowed(int nid, nodemask_t *nodes_allowed)
> +{
> +	if (!node_isset(nid, *nodes_allowed))
> +		nid = next_node_allowed(nid, nodes_allowed);
> +	return nid;
> +}
> +
> +/*
>   * Use a helper variable to find the next node and then
>   * copy it back to next_nid_to_alloc afterwards:
>   * otherwise there's a window in which a racer might
>   * pass invalid nid MAX_NUMNODES to alloc_pages_exact_node.
>   * But we don't need to use a spin_lock here: it really
>   * doesn't matter if occasionally a racer chooses the
> - * same nid as we do.  Move nid forward in the mask even
> - * if we just successfully allocated a hugepage so that
> - * the next caller gets hugepages on the next node.
> + * same nid as we do.  Move nid forward in the mask whether
> + * or not we just successfully allocated a hugepage so that
> + * the next allocation addresses the next node.
>   */
>  static int hstate_next_node_to_alloc(struct hstate *h,
>  					nodemask_t *nodes_allowed)
>  {
> -	int next_nid;
> +	int nid, next_nid;
>  
>  	if (!nodes_allowed)
>  		nodes_allowed = &node_online_map;
>  
> -	next_nid = next_node(h->next_nid_to_alloc, *nodes_allowed);
> -	if (next_nid == MAX_NUMNODES)
> -		next_nid = first_node(*nodes_allowed);
> +	nid = this_node_allowed(h->next_nid_to_alloc, nodes_allowed);
> +
> +	next_nid = next_node_allowed(nid, nodes_allowed);
>  	h->next_nid_to_alloc = next_nid;
> -	return next_nid;
> +
> +	return nid;
>  }
>  
>  static int alloc_fresh_huge_page(struct hstate *h, nodemask_t *nodes_allowed)
> @@ -653,15 +678,17 @@ static int alloc_fresh_huge_page(struct 
>  	int next_nid;
>  	int ret = 0;
>  
> -	start_nid = h->next_nid_to_alloc;
> +	start_nid = hstate_next_node_to_alloc(h, nodes_allowed);
>  	next_nid = start_nid;
>  
>  	do {
>  		page = alloc_fresh_huge_page_node(h, next_nid);
> -		if (page)
> +		if (page) {
>  			ret = 1;
> +			break;
> +		}
>  		next_nid = hstate_next_node_to_alloc(h, nodes_allowed);
> -	} while (!page && next_nid != start_nid);
> +	} while (next_nid != start_nid);
>  
>  	if (ret)
>  		count_vm_event(HTLB_BUDDY_PGALLOC);
> @@ -672,21 +699,23 @@ static int alloc_fresh_huge_page(struct 
>  }
>  
>  /*
> - * helper for free_pool_huge_page() - find next node
> - * from which to free a huge page
> + * helper for free_pool_huge_page() - return the next node
> + * from which to free a huge page.  Advance the next node id
> + * whether or not we find a free huge page to free so that the
> + * next attempt to free addresses the next node.
>   */
>  static int hstate_next_node_to_free(struct hstate *h, nodemask_t *nodes_allowed)
>  {
> -	int next_nid;
> +	int nid, next_nid;
>  
>  	if (!nodes_allowed)
>  		nodes_allowed = &node_online_map;
>  
> -	next_nid = next_node(h->next_nid_to_free, *nodes_allowed);
> -	if (next_nid == MAX_NUMNODES)
> -		next_nid = first_node(*nodes_allowed);
> +	nid = this_node_allowed(h->next_nid_to_free, nodes_allowed);
> +	next_nid = next_node_allowed(nid, nodes_allowed);
>  	h->next_nid_to_free = next_nid;
> -	return next_nid;
> +
> +	return nid;
>  }
>  
>  /*
> @@ -702,7 +731,7 @@ static int free_pool_huge_page(struct hs
>  	int next_nid;
>  	int ret = 0;
>  
> -	start_nid = h->next_nid_to_free;
> +	start_nid = hstate_next_node_to_free(h, nodes_allowed);
>  	next_nid = start_nid;
>  
>  	do {
> @@ -724,9 +753,10 @@ static int free_pool_huge_page(struct hs
>  			}
>  			update_and_free_page(h, page);
>  			ret = 1;
> +			break;
>  		}
>   		next_nid = hstate_next_node_to_free(h, nodes_allowed);
> -	} while (!ret && next_nid != start_nid);
> +	} while (next_nid != start_nid);
>  
>  	return ret;
>  }
> @@ -1037,10 +1067,9 @@ int __weak alloc_bootmem_huge_page(struc
>  		void *addr;
>  
>  		addr = __alloc_bootmem_node_nopanic(
> -				NODE_DATA(h->next_nid_to_alloc),
> +				NODE_DATA(hstate_next_node_to_alloc(h, NULL)),
>  				huge_page_size(h), huge_page_size(h), 0);
>  
> -		hstate_next_node_to_alloc(h, NULL); /* always advance nid */
>  		if (addr) {
>  			/*
>  			 * Use the beginning of the huge page to store the
> @@ -1177,29 +1206,33 @@ static int adjust_pool_surplus(struct hs
>  	VM_BUG_ON(delta != -1 && delta != 1);
>  
>  	if (delta < 0)
> -		start_nid = h->next_nid_to_alloc;
> +		start_nid = hstate_next_node_to_alloc(h, nodes_allowed);
>  	else
> -		start_nid = h->next_nid_to_free;
> +		start_nid = hstate_next_node_to_free(h, nodes_allowed);
>  	next_nid = start_nid;
>  
>  	do {
>  		int nid = next_nid;
>  		if (delta < 0)  {
> -			next_nid = hstate_next_node_to_alloc(h, nodes_allowed);
>  			/*
>  			 * To shrink on this node, there must be a surplus page
>  			 */
> -			if (!h->surplus_huge_pages_node[nid])
> +			if (!h->surplus_huge_pages_node[nid]) {
> +				next_nid = hstate_next_node_to_alloc(h,
> +								nodes_allowed);
>  				continue;
> +			}
>  		}
>  		if (delta > 0) {
> -			next_nid = hstate_next_node_to_free(h, nodes_allowed);
>  			/*
>  			 * Surplus cannot exceed the total number of pages
>  			 */
>  			if (h->surplus_huge_pages_node[nid] >=
> -						h->nr_huge_pages_node[nid])
> +						h->nr_huge_pages_node[nid]) {
> +				next_nid = hstate_next_node_to_free(h,
> +								nodes_allowed);
>  				continue;
> +			}
>  		}
>  
>  		h->surplus_huge_pages += delta;
> @@ -1215,10 +1248,13 @@ static int adjust_pool_surplus(struct hs
>  static unsigned long set_max_huge_pages(struct hstate *h, unsigned long count)
>  {
>  	unsigned long min_count, ret;
> +	nodemask_t *nodes_allowed;
>  
>  	if (h->order >= MAX_ORDER)
>  		return h->max_huge_pages;
>  
> +	nodes_allowed = huge_mpol_nodes_allowed();
> +
>  	/*
>  	 * Increase the pool size
>  	 * First take pages out of surplus state.  Then make up the
> @@ -1232,7 +1268,7 @@ static unsigned long set_max_huge_pages(
>  	 */
>  	spin_lock(&hugetlb_lock);
>  	while (h->surplus_huge_pages && count > persistent_huge_pages(h)) {
> -		if (!adjust_pool_surplus(h, NULL, -1))
> +		if (!adjust_pool_surplus(h, nodes_allowed, -1))
>  			break;
>  	}
>  
> @@ -1243,7 +1279,7 @@ static unsigned long set_max_huge_pages(
>  		 * and reducing the surplus.
>  		 */
>  		spin_unlock(&hugetlb_lock);
> -		ret = alloc_fresh_huge_page(h, NULL);
> +		ret = alloc_fresh_huge_page(h, nodes_allowed);
>  		spin_lock(&hugetlb_lock);
>  		if (!ret)
>  			goto out;
> @@ -1269,16 +1305,17 @@ static unsigned long set_max_huge_pages(
>  	min_count = max(count, min_count);
>  	try_to_free_low(h, min_count);
>  	while (min_count < persistent_huge_pages(h)) {
> -		if (!free_pool_huge_page(h, NULL, 0))
> +		if (!free_pool_huge_page(h, nodes_allowed, 0))
>  			break;
>  	}
>  	while (count < persistent_huge_pages(h)) {
> -		if (!adjust_pool_surplus(h, NULL, 1))
> +		if (!adjust_pool_surplus(h, nodes_allowed, 1))
>  			break;
>  	}
>  out:
>  	ret = persistent_huge_pages(h);
>  	spin_unlock(&hugetlb_lock);
> +	kfree(nodes_allowed);
>  	return ret;
>  }
>  
> Index: linux-2.6.31-rc1-mmotm-090625-1549/mm/mempolicy.c
> ===================================================================
> --- linux-2.6.31-rc1-mmotm-090625-1549.orig/mm/mempolicy.c	2009-07-07 09:46:48.000000000 -0400
> +++ linux-2.6.31-rc1-mmotm-090625-1549/mm/mempolicy.c	2009-07-07 13:48:06.000000000 -0400
> @@ -1544,6 +1544,67 @@ struct zonelist *huge_zonelist(struct vm
>  	}
>  	return zl;
>  }
> +
> +/*
> + * huge_mpol_nodes_allowed -- mempolicy extension for huge pages.
> + *
> + * Returns a [pointer to a] nodelist based on the current task's mempolicy
> + * to constraing the allocation and freeing of persistent huge pages
> + * 'Preferred', 'local' and 'interleave' mempolicy will behave more like
> + * 'bind' policy in this context.  An attempt to allocate a persistent huge
> + * page will never "fallback" to another node inside the buddy system
> + * allocator.
> + *
> + * If the task's mempolicy is "default" [NULL], just return NULL for
> + * default behavior.  Otherwise, extract the policy nodemask for 'bind'
> + * or 'interleave' policy or construct a nodemask for 'preferred' or
> + * 'local' policy and return a pointer to a kmalloc()ed nodemask_t.
> + *
> + * N.B., it is the caller's responsibility to free a returned nodemask.
> + */
> +nodemask_t *huge_mpol_nodes_allowed(void)
> +{
> +	nodemask_t *nodes_allowed = NULL;
> +	struct mempolicy *mempolicy;
> +	int nid;
> +
> +	if (!current->mempolicy)
> +		return NULL;
> +
> +	mpol_get(current->mempolicy);
> +	nodes_allowed = kmalloc(sizeof(*nodes_allowed), GFP_KERNEL);
> +	if (!nodes_allowed) {
> +		printk(KERN_WARNING "%s unable to allocate nodes allowed mask "
> +			"for huge page allocation.\nFalling back to default.\n",
> +			current->comm);
> +		goto out;
> +	}
> +	nodes_clear(*nodes_allowed);
> +
> +	mempolicy = current->mempolicy;
> +	switch(mempolicy->mode) {
> +	case MPOL_PREFERRED:
> +		if (mempolicy->flags & MPOL_F_LOCAL)
> +			nid = numa_node_id();
> +		else
> +			nid = mempolicy->v.preferred_node;
> +		node_set(nid, *nodes_allowed);
> +		break;
> +
> +	case MPOL_BIND:
> +		/* Fall through */
> +	case MPOL_INTERLEAVE:
> +		*nodes_allowed =  mempolicy->v.nodes;
> +		break;
> +
> +	default:
> +		BUG();
> +	}
> +
> +out:
> +	mpol_put(current->mempolicy);
> +	return nodes_allowed;
> +}
>  #endif
>  
>  /* Allocate a page in interleaved policy.
> Index: linux-2.6.31-rc1-mmotm-090625-1549/include/linux/mempolicy.h
> ===================================================================
> --- linux-2.6.31-rc1-mmotm-090625-1549.orig/include/linux/mempolicy.h	2009-07-06 13:05:23.000000000 -0400
> +++ linux-2.6.31-rc1-mmotm-090625-1549/include/linux/mempolicy.h	2009-07-07 09:58:32.000000000 -0400
> @@ -201,6 +201,7 @@ extern void mpol_fix_fork_child_flag(str
>  extern struct zonelist *huge_zonelist(struct vm_area_struct *vma,
>  				unsigned long addr, gfp_t gfp_flags,
>  				struct mempolicy **mpol, nodemask_t **nodemask);
> +extern nodemask_t *huge_mpol_nodes_allowed(void);
>  extern unsigned slab_node(struct mempolicy *policy);
>  
>  extern enum zone_type policy_zone;
> @@ -328,6 +329,8 @@ static inline struct zonelist *huge_zone
>  	return node_zonelist(0, gfp_flags);
>  }
>  
> +static inline nodemask_t *huge_mpol_nodes_allowed(void) { return NULL; }
> +
>  static inline int do_migrate_pages(struct mm_struct *mm,
>  			const nodemask_t *from_nodes,
>  			const nodemask_t *to_nodes, int flags)
> 

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab

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Re: [PATCH 2/3] hugetlb: derive huge pages nodes allowed from task mempolicy

[Mel Gorman]

On Thu, Jul 09, 2009 at 02:30:20PM +0100, Mel Gorman wrote:
> On Wed, Jul 08, 2009 at 03:24:46PM -0400, Lee Schermerhorn wrote:
> > [PATCH 2/3] hugetlb:  derive huge pages nodes allowed from task mempolicy
> > 
> > Against: 25jun09 mmotm atop the "hugetlb: balance freeing..." series
> > 
> > V2:
> > + cleaned up comments, removed some deemed unnecessary,
> >   add some suggested by review
> > + removed check for !current in huge_mpol_nodes_allowed().
> > + added 'current->comm' to warning message in huge_mpol_nodes_allowed().
> > + added VM_BUG_ON() assertion in hugetlb.c next_node_allowed() to
> >   catch out of range node id.
> > + add examples to patch description
> > 
> > This patch derives a "nodes_allowed" node mask from the numa
> > mempolicy of the task modifying the number of persistent huge
> > pages to control the allocation, freeing and adjusting of surplus
> > huge pages.  This mask is derived as follows:
> > 
> > * For "default" [NULL] task mempolicy, a NULL nodemask_t pointer
> >   is produced.  This will cause the hugetlb subsystem to use
> >   node_online_map as the "nodes_allowed".  This preserves the
> >   behavior before this patch.
> > * For "preferred" mempolicy, including explicit local allocation,
> >   a nodemask with the single preferred node will be produced. 
> >   "local" policy will NOT track any internode migrations of the
> >   task adjusting nr_hugepages.
> > * For "bind" and "interleave" policy, the mempolicy's nodemask
> >   will be used.
> > * Other than to inform the construction of the nodes_allowed node
> >   mask, the actual mempolicy mode is ignored.  That is, all modes
> >   behave like interleave over the resulting nodes_allowed mask
> >   with no "fallback".
> > 
> > Because we may have allocated or freed a huge page with a 
> > different policy/nodes_allowed previously, we always need to
> > check that the next_node_to_{alloc|free} exists in the current
> > nodes_allowed mask.  To avoid duplication of code, this is done
> > in the hstate_next_node_to_{alloc|free}() functions.  So,
> > these functions have been modified to allow them to be called
> > to obtain the "start_nid".  Then, whereas prior to this patch
> > we unconditionally called hstate_next_node_to_{alloc|free}(),
> > whether or not we successfully allocated/freed a huge page on
> > the node, now we only call these functions on failure to alloc/free.
> > 
> > Notes:
> > 
> > 1) This patch introduces a subtle change in behavior:  huge page
> >    allocation and freeing will be constrained by any mempolicy
> >    that the task adjusting the huge page pool inherits from its
> >    parent.  This policy could come from a distant ancestor.  The
> >    adminstrator adjusting the huge page pool without explicitly
> >    specifying a mempolicy via numactl might be surprised by this.
> >    Additionaly, any mempolicy specified by numactl will be
> >    constrained by the cpuset in which numactl is invoked.
> > 
> > 2) Hugepages allocated at boot time use the node_online_map.
> >    An additional patch could implement a temporary boot time
> >    huge pages nodes_allowed command line parameter.
> > 
> > 3) Using mempolicy to control persistent huge page allocation
> >    and freeing requires no change to hugeadm when invoking
> >    it via numactl, as shown in the examples below.  However,
> >    hugeadm could be enhanced to take the allowed nodes as an
> >    argument and set its task mempolicy itself.  This would allow
> >    it to detect and warn about any non-default mempolicy that it
> >    inherited from its parent, thus alleviating the issue described
> >    in Note 1 above.
> > 
> > See the updated documentation [next patch] for more information
> > about the implications of this patch.
> > 
> > Examples:
> > 
> > Starting with:
> > 
> > 	Node 0 HugePages_Total:     0
> > 	Node 1 HugePages_Total:     0
> > 	Node 2 HugePages_Total:     0
> > 	Node 3 HugePages_Total:     0
> > 
> > Default behavior [with or without this patch] balances persistent
> > hugepage allocation across nodes [with sufficient contiguous memory]:
> > 
> > 	hugeadm --pool-pages-min=2048Kb:32
> > 
> > yields:
> > 
> > 	Node 0 HugePages_Total:     8
> > 	Node 1 HugePages_Total:     8
> > 	Node 2 HugePages_Total:     8
> > 	Node 3 HugePages_Total:     8
> > 
> > Applying mempolicy--e.g., with numactl [using '-m' a.k.a.
> > '--membind' because it allows multiple nodes to be specified
> > and it's easy to type]--we can allocate huge pages on
> > individual nodes or sets of nodes.  So, starting from the 
> > condition above, with 8 huge pages per node:
> > 
> > 	numactl -m 2 hugeadm --pool-pages-min=2048Kb:+8
> > 
> > yields:
> > 
> > 	Node 0 HugePages_Total:     8
> > 	Node 1 HugePages_Total:     8
> > 	Node 2 HugePages_Total:    16
> > 	Node 3 HugePages_Total:     8
> > 
> > The incremental 8 huge pages were restricted to node 2 by the
> > specified mempolicy.
> > 
> > Similarly, we can use mempolicy to free persistent huge pages
> > from specified nodes:
> > 
> > 	numactl -m 0,1 hugeadm --pool-pages-min=2048Kb:-8
> > 
> > yields:
> > 
> > 	Node 0 HugePages_Total:     4
> > 	Node 1 HugePages_Total:     4
> > 	Node 2 HugePages_Total:    16
> > 	Node 3 HugePages_Total:     8
> > 
> > The 8 huge pages freed were balanced over nodes 0 and 1.
> > 
> > Signed-off-by: Lee Schermerhorn <lee.schermerhorn@hp.com>
> > 
> 
> Much better changelog.
> 
> Reading through, the main problem I can see is that the reservation
> calculations are still not nodemask aware. This means that mmap() can return
> successfully and the process that called mmap() get unexpectedly killed
> because while there were enough hugepages overall, there were not enough in
> the pools allowed by the nodemask. This is a stability problem for those that
> create hugepage pools on one set of nodes and run applications on a subset.
> Minimally, can this situation be warned about and a note in the documentation
> about it?
> 
> Testing with it, I couldn't break it as such but libhugetlbfs is showing up
> an anomaly with the counters tests. Some investigation showed that it was
> because when it shrinks the pool, one page gets accounted for as a surplus
> page which was unexpected.
> 
> I only got as far as determining the problem was in the patches that free
> pages in a round-robin fashion but then ran out of time on the machine. I'll
> see can I reproduce using fake-numa on a normal x86-64 instead of a real
> NUMA machine but maybe you have a fix for this problem already?
> 

Bah, you did. After I hit send, I remembered you sent one out and I didn't
pick it up properly. The counters tests works as expected now. I'll keep
testing but other than the stability problem when running on a subset of
nodes with hugepages, this looks good to me.

Reviewed-by: Mel Gorman <mel@csn.ul.ie>

> >  include/linux/mempolicy.h |    3 +
> >  mm/hugetlb.c              |  101 +++++++++++++++++++++++++++++++---------------
> >  mm/mempolicy.c            |   61 +++++++++++++++++++++++++++
> >  3 files changed, 133 insertions(+), 32 deletions(-)
> > 
> > Index: linux-2.6.31-rc1-mmotm-090625-1549/mm/hugetlb.c
> > ===================================================================
> > --- linux-2.6.31-rc1-mmotm-090625-1549.orig/mm/hugetlb.c	2009-07-07 09:58:17.000000000 -0400
> > +++ linux-2.6.31-rc1-mmotm-090625-1549/mm/hugetlb.c	2009-07-07 13:25:41.000000000 -0400
> > @@ -621,29 +621,54 @@ static struct page *alloc_fresh_huge_pag
> >  }
> >  
> >  /*
> > + * common helper functions for hstate_next_node_to_{alloc|free}.
> > + * We may have allocated or freed a huge pages based on a different
> > + * nodes_allowed, previously, so h->next_node_to_{alloc|free} might
> > + * be outside of *nodes_allowed.  Ensure that we use the next
> > + * allowed node for alloc or free.
> > + */
> > +static int next_node_allowed(int nid, nodemask_t *nodes_allowed)
> > +{
> > +	nid = next_node(nid, *nodes_allowed);
> > +	if (nid == MAX_NUMNODES)
> > +		nid = first_node(*nodes_allowed);
> > +	VM_BUG_ON(nid >= MAX_NUMNODES);
> > +
> > +	return nid;
> > +}
> > +
> > +static int this_node_allowed(int nid, nodemask_t *nodes_allowed)
> > +{
> > +	if (!node_isset(nid, *nodes_allowed))
> > +		nid = next_node_allowed(nid, nodes_allowed);
> > +	return nid;
> > +}
> > +
> > +/*
> >   * Use a helper variable to find the next node and then
> >   * copy it back to next_nid_to_alloc afterwards:
> >   * otherwise there's a window in which a racer might
> >   * pass invalid nid MAX_NUMNODES to alloc_pages_exact_node.
> >   * But we don't need to use a spin_lock here: it really
> >   * doesn't matter if occasionally a racer chooses the
> > - * same nid as we do.  Move nid forward in the mask even
> > - * if we just successfully allocated a hugepage so that
> > - * the next caller gets hugepages on the next node.
> > + * same nid as we do.  Move nid forward in the mask whether
> > + * or not we just successfully allocated a hugepage so that
> > + * the next allocation addresses the next node.
> >   */
> >  static int hstate_next_node_to_alloc(struct hstate *h,
> >  					nodemask_t *nodes_allowed)
> >  {
> > -	int next_nid;
> > +	int nid, next_nid;
> >  
> >  	if (!nodes_allowed)
> >  		nodes_allowed = &node_online_map;
> >  
> > -	next_nid = next_node(h->next_nid_to_alloc, *nodes_allowed);
> > -	if (next_nid == MAX_NUMNODES)
> > -		next_nid = first_node(*nodes_allowed);
> > +	nid = this_node_allowed(h->next_nid_to_alloc, nodes_allowed);
> > +
> > +	next_nid = next_node_allowed(nid, nodes_allowed);
> >  	h->next_nid_to_alloc = next_nid;
> > -	return next_nid;
> > +
> > +	return nid;
> >  }
> >  
> >  static int alloc_fresh_huge_page(struct hstate *h, nodemask_t *nodes_allowed)
> > @@ -653,15 +678,17 @@ static int alloc_fresh_huge_page(struct 
> >  	int next_nid;
> >  	int ret = 0;
> >  
> > -	start_nid = h->next_nid_to_alloc;
> > +	start_nid = hstate_next_node_to_alloc(h, nodes_allowed);
> >  	next_nid = start_nid;
> >  
> >  	do {
> >  		page = alloc_fresh_huge_page_node(h, next_nid);
> > -		if (page)
> > +		if (page) {
> >  			ret = 1;
> > +			break;
> > +		}
> >  		next_nid = hstate_next_node_to_alloc(h, nodes_allowed);
> > -	} while (!page && next_nid != start_nid);
> > +	} while (next_nid != start_nid);
> >  
> >  	if (ret)
> >  		count_vm_event(HTLB_BUDDY_PGALLOC);
> > @@ -672,21 +699,23 @@ static int alloc_fresh_huge_page(struct 
> >  }
> >  
> >  /*
> > - * helper for free_pool_huge_page() - find next node
> > - * from which to free a huge page
> > + * helper for free_pool_huge_page() - return the next node
> > + * from which to free a huge page.  Advance the next node id
> > + * whether or not we find a free huge page to free so that the
> > + * next attempt to free addresses the next node.
> >   */
> >  static int hstate_next_node_to_free(struct hstate *h, nodemask_t *nodes_allowed)
> >  {
> > -	int next_nid;
> > +	int nid, next_nid;
> >  
> >  	if (!nodes_allowed)
> >  		nodes_allowed = &node_online_map;
> >  
> > -	next_nid = next_node(h->next_nid_to_free, *nodes_allowed);
> > -	if (next_nid == MAX_NUMNODES)
> > -		next_nid = first_node(*nodes_allowed);
> > +	nid = this_node_allowed(h->next_nid_to_free, nodes_allowed);
> > +	next_nid = next_node_allowed(nid, nodes_allowed);
> >  	h->next_nid_to_free = next_nid;
> > -	return next_nid;
> > +
> > +	return nid;
> >  }
> >  
> >  /*
> > @@ -702,7 +731,7 @@ static int free_pool_huge_page(struct hs
> >  	int next_nid;
> >  	int ret = 0;
> >  
> > -	start_nid = h->next_nid_to_free;
> > +	start_nid = hstate_next_node_to_free(h, nodes_allowed);
> >  	next_nid = start_nid;
> >  
> >  	do {
> > @@ -724,9 +753,10 @@ static int free_pool_huge_page(struct hs
> >  			}
> >  			update_and_free_page(h, page);
> >  			ret = 1;
> > +			break;
> >  		}
> >   		next_nid = hstate_next_node_to_free(h, nodes_allowed);
> > -	} while (!ret && next_nid != start_nid);
> > +	} while (next_nid != start_nid);
> >  
> >  	return ret;
> >  }
> > @@ -1037,10 +1067,9 @@ int __weak alloc_bootmem_huge_page(struc
> >  		void *addr;
> >  
> >  		addr = __alloc_bootmem_node_nopanic(
> > -				NODE_DATA(h->next_nid_to_alloc),
> > +				NODE_DATA(hstate_next_node_to_alloc(h, NULL)),
> >  				huge_page_size(h), huge_page_size(h), 0);
> >  
> > -		hstate_next_node_to_alloc(h, NULL); /* always advance nid */
> >  		if (addr) {
> >  			/*
> >  			 * Use the beginning of the huge page to store the
> > @@ -1177,29 +1206,33 @@ static int adjust_pool_surplus(struct hs
> >  	VM_BUG_ON(delta != -1 && delta != 1);
> >  
> >  	if (delta < 0)
> > -		start_nid = h->next_nid_to_alloc;
> > +		start_nid = hstate_next_node_to_alloc(h, nodes_allowed);
> >  	else
> > -		start_nid = h->next_nid_to_free;
> > +		start_nid = hstate_next_node_to_free(h, nodes_allowed);
> >  	next_nid = start_nid;
> >  
> >  	do {
> >  		int nid = next_nid;
> >  		if (delta < 0)  {
> > -			next_nid = hstate_next_node_to_alloc(h, nodes_allowed);
> >  			/*
> >  			 * To shrink on this node, there must be a surplus page
> >  			 */
> > -			if (!h->surplus_huge_pages_node[nid])
> > +			if (!h->surplus_huge_pages_node[nid]) {
> > +				next_nid = hstate_next_node_to_alloc(h,
> > +								nodes_allowed);
> >  				continue;
> > +			}
> >  		}
> >  		if (delta > 0) {
> > -			next_nid = hstate_next_node_to_free(h, nodes_allowed);
> >  			/*
> >  			 * Surplus cannot exceed the total number of pages
> >  			 */
> >  			if (h->surplus_huge_pages_node[nid] >=
> > -						h->nr_huge_pages_node[nid])
> > +						h->nr_huge_pages_node[nid]) {
> > +				next_nid = hstate_next_node_to_free(h,
> > +								nodes_allowed);
> >  				continue;
> > +			}
> >  		}
> >  
> >  		h->surplus_huge_pages += delta;
> > @@ -1215,10 +1248,13 @@ static int adjust_pool_surplus(struct hs
> >  static unsigned long set_max_huge_pages(struct hstate *h, unsigned long count)
> >  {
> >  	unsigned long min_count, ret;
> > +	nodemask_t *nodes_allowed;
> >  
> >  	if (h->order >= MAX_ORDER)
> >  		return h->max_huge_pages;
> >  
> > +	nodes_allowed = huge_mpol_nodes_allowed();
> > +
> >  	/*
> >  	 * Increase the pool size
> >  	 * First take pages out of surplus state.  Then make up the
> > @@ -1232,7 +1268,7 @@ static unsigned long set_max_huge_pages(
> >  	 */
> >  	spin_lock(&hugetlb_lock);
> >  	while (h->surplus_huge_pages && count > persistent_huge_pages(h)) {
> > -		if (!adjust_pool_surplus(h, NULL, -1))
> > +		if (!adjust_pool_surplus(h, nodes_allowed, -1))
> >  			break;
> >  	}
> >  
> > @@ -1243,7 +1279,7 @@ static unsigned long set_max_huge_pages(
> >  		 * and reducing the surplus.
> >  		 */
> >  		spin_unlock(&hugetlb_lock);
> > -		ret = alloc_fresh_huge_page(h, NULL);
> > +		ret = alloc_fresh_huge_page(h, nodes_allowed);
> >  		spin_lock(&hugetlb_lock);
> >  		if (!ret)
> >  			goto out;
> > @@ -1269,16 +1305,17 @@ static unsigned long set_max_huge_pages(
> >  	min_count = max(count, min_count);
> >  	try_to_free_low(h, min_count);
> >  	while (min_count < persistent_huge_pages(h)) {
> > -		if (!free_pool_huge_page(h, NULL, 0))
> > +		if (!free_pool_huge_page(h, nodes_allowed, 0))
> >  			break;
> >  	}
> >  	while (count < persistent_huge_pages(h)) {
> > -		if (!adjust_pool_surplus(h, NULL, 1))
> > +		if (!adjust_pool_surplus(h, nodes_allowed, 1))
> >  			break;
> >  	}
> >  out:
> >  	ret = persistent_huge_pages(h);
> >  	spin_unlock(&hugetlb_lock);
> > +	kfree(nodes_allowed);
> >  	return ret;
> >  }
> >  
> > Index: linux-2.6.31-rc1-mmotm-090625-1549/mm/mempolicy.c
> > ===================================================================
> > --- linux-2.6.31-rc1-mmotm-090625-1549.orig/mm/mempolicy.c	2009-07-07 09:46:48.000000000 -0400
> > +++ linux-2.6.31-rc1-mmotm-090625-1549/mm/mempolicy.c	2009-07-07 13:48:06.000000000 -0400
> > @@ -1544,6 +1544,67 @@ struct zonelist *huge_zonelist(struct vm
> >  	}
> >  	return zl;
> >  }
> > +
> > +/*
> > + * huge_mpol_nodes_allowed -- mempolicy extension for huge pages.
> > + *
> > + * Returns a [pointer to a] nodelist based on the current task's mempolicy
> > + * to constraing the allocation and freeing of persistent huge pages
> > + * 'Preferred', 'local' and 'interleave' mempolicy will behave more like
> > + * 'bind' policy in this context.  An attempt to allocate a persistent huge
> > + * page will never "fallback" to another node inside the buddy system
> > + * allocator.
> > + *
> > + * If the task's mempolicy is "default" [NULL], just return NULL for
> > + * default behavior.  Otherwise, extract the policy nodemask for 'bind'
> > + * or 'interleave' policy or construct a nodemask for 'preferred' or
> > + * 'local' policy and return a pointer to a kmalloc()ed nodemask_t.
> > + *
> > + * N.B., it is the caller's responsibility to free a returned nodemask.
> > + */
> > +nodemask_t *huge_mpol_nodes_allowed(void)
> > +{
> > +	nodemask_t *nodes_allowed = NULL;
> > +	struct mempolicy *mempolicy;
> > +	int nid;
> > +
> > +	if (!current->mempolicy)
> > +		return NULL;
> > +
> > +	mpol_get(current->mempolicy);
> > +	nodes_allowed = kmalloc(sizeof(*nodes_allowed), GFP_KERNEL);
> > +	if (!nodes_allowed) {
> > +		printk(KERN_WARNING "%s unable to allocate nodes allowed mask "
> > +			"for huge page allocation.\nFalling back to default.\n",
> > +			current->comm);
> > +		goto out;
> > +	}
> > +	nodes_clear(*nodes_allowed);
> > +
> > +	mempolicy = current->mempolicy;
> > +	switch(mempolicy->mode) {
> > +	case MPOL_PREFERRED:
> > +		if (mempolicy->flags & MPOL_F_LOCAL)
> > +			nid = numa_node_id();
> > +		else
> > +			nid = mempolicy->v.preferred_node;
> > +		node_set(nid, *nodes_allowed);
> > +		break;
> > +
> > +	case MPOL_BIND:
> > +		/* Fall through */
> > +	case MPOL_INTERLEAVE:
> > +		*nodes_allowed =  mempolicy->v.nodes;
> > +		break;
> > +
> > +	default:
> > +		BUG();
> > +	}
> > +
> > +out:
> > +	mpol_put(current->mempolicy);
> > +	return nodes_allowed;
> > +}
> >  #endif
> >  
> >  /* Allocate a page in interleaved policy.
> > Index: linux-2.6.31-rc1-mmotm-090625-1549/include/linux/mempolicy.h
> > ===================================================================
> > --- linux-2.6.31-rc1-mmotm-090625-1549.orig/include/linux/mempolicy.h	2009-07-06 13:05:23.000000000 -0400
> > +++ linux-2.6.31-rc1-mmotm-090625-1549/include/linux/mempolicy.h	2009-07-07 09:58:32.000000000 -0400
> > @@ -201,6 +201,7 @@ extern void mpol_fix_fork_child_flag(str
> >  extern struct zonelist *huge_zonelist(struct vm_area_struct *vma,
> >  				unsigned long addr, gfp_t gfp_flags,
> >  				struct mempolicy **mpol, nodemask_t **nodemask);
> > +extern nodemask_t *huge_mpol_nodes_allowed(void);
> >  extern unsigned slab_node(struct mempolicy *policy);
> >  
> >  extern enum zone_type policy_zone;
> > @@ -328,6 +329,8 @@ static inline struct zonelist *huge_zone
> >  	return node_zonelist(0, gfp_flags);
> >  }
> >  
> > +static inline nodemask_t *huge_mpol_nodes_allowed(void) { return NULL; }
> > +
> >  static inline int do_migrate_pages(struct mm_struct *mm,
> >  			const nodemask_t *from_nodes,
> >  			const nodemask_t *to_nodes, int flags)
> > 
> 
> -- 
> Mel Gorman
> Part-time Phd Student                          Linux Technology Center
> University of Limerick                         IBM Dublin Software Lab
> 
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@kvack.org.  For more info on Linux MM,
> see: http://www.linux-mm.org/ .
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> 

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab

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[PATCH 3/3] hugetlb: update hugetlb documentation for mempolicy based management.

[Lee Schermerhorn]

PATCH 3/3 hugetlb:  update hugetlb documentation for mempolicy based management.

Against:  25jun09 mmotm atop the "balance freeing of huge pages" series

This patch updates the kernel huge tlb documentation to describe the
numa memory policy based huge page management.  Additionaly, the patch
includes a fair amount of rework to improve consistency, eliminate
duplication and set the context for documenting the memory policy
interaction.

Signed-off-by: Lee Schermerhorn <lee.schermerhorn@hp.com>

 Documentation/vm/hugetlbpage.txt |  228 ++++++++++++++++++++++++---------------
 1 file changed, 143 insertions(+), 85 deletions(-)

Index: linux-2.6.31-rc1-mmotm-090625-1549/Documentation/vm/hugetlbpage.txt
===================================================================
--- linux-2.6.31-rc1-mmotm-090625-1549.orig/Documentation/vm/hugetlbpage.txt	2009-07-07 09:58:14.000000000 -0400
+++ linux-2.6.31-rc1-mmotm-090625-1549/Documentation/vm/hugetlbpage.txt	2009-07-07 09:58:26.000000000 -0400
@@ -11,23 +11,21 @@ This optimization is more critical now a
 (several GBs) are more readily available.
 
 Users can use the huge page support in Linux kernel by either using the mmap
-system call or standard SYSv shared memory system calls (shmget, shmat).
+system call or standard SYSV shared memory system calls (shmget, shmat).
 
 First the Linux kernel needs to be built with the CONFIG_HUGETLBFS
 (present under "File systems") and CONFIG_HUGETLB_PAGE (selected
 automatically when CONFIG_HUGETLBFS is selected) configuration
 options.
 
-The kernel built with huge page support should show the number of configured
-huge pages in the system by running the "cat /proc/meminfo" command.
+The /proc/meminfo file provides information about the total number of hugetlb
+pages preallocated in the kernel's huge page pool.  It also displays
+information about the number of free, reserved and surplus huge pages and the
+[default] huge page size.  The huge page size is needed for generating the
+proper alignment and size of the arguments to system calls that map huge page
+regions.
 
-/proc/meminfo also provides information about the total number of hugetlb
-pages configured in the kernel.  It also displays information about the
-number of free hugetlb pages at any time.  It also displays information about
-the configured huge page size - this is needed for generating the proper
-alignment and size of the arguments to the above system calls.
-
-The output of "cat /proc/meminfo" will have lines like:
+The output of "cat /proc/meminfo" will include lines like:
 
 .....
 HugePages_Total: vvv
@@ -53,26 +51,25 @@ HugePages_Surp  is short for "surplus," 
 /proc/filesystems should also show a filesystem of type "hugetlbfs" configured
 in the kernel.
 
-/proc/sys/vm/nr_hugepages indicates the current number of configured hugetlb
-pages in the kernel.  Super user can dynamically request more (or free some
-pre-configured) huge pages.
-The allocation (or deallocation) of hugetlb pages is possible only if there are
-enough physically contiguous free pages in system (freeing of huge pages is
-possible only if there are enough hugetlb pages free that can be transferred
-back to regular memory pool).
-
-Pages that are used as hugetlb pages are reserved inside the kernel and cannot
-be used for other purposes.
-
-Once the kernel with Hugetlb page support is built and running, a user can
-use either the mmap system call or shared memory system calls to start using
-the huge pages.  It is required that the system administrator preallocate
-enough memory for huge page purposes.
-
-The administrator can preallocate huge pages on the kernel boot command line by
-specifying the "hugepages=N" parameter, where 'N' = the number of huge pages
-requested.  This is the most reliable method for preallocating huge pages as
-memory has not yet become fragmented.
+/proc/sys/vm/nr_hugepages indicates the current number of huge pages pre-
+allocated in the kernel's huge page pool.  These are called "persistent"
+huge pages.  A user with root privileges can dynamically allocate more or
+free some persistent huge pages by increasing or decreasing the value of
+'nr_hugepages'.
+
+Pages that are used as huge pages are reserved inside the kernel and cannot
+be used for other purposes.  Huge pages can not be swapped out under
+memory pressure.
+
+Once a number of huge pages have been pre-allocated to the kernel huge page
+pool, a user with appropriate privilege can use either the mmap system call
+or shared memory system calls to use the huge pages.  See the discussion of
+Using Huge Pages, below
+
+The administrator can preallocate persistent huge pages on the kernel boot
+command line by specifying the "hugepages=N" parameter, where 'N' = the
+number of requested huge pages requested.  This is the most reliable method
+or preallocating huge pages as memory has not yet become fragmented.
 
 Some platforms support multiple huge page sizes.  To preallocate huge pages
 of a specific size, one must preceed the huge pages boot command parameters
@@ -80,19 +77,23 @@ with a huge page size selection paramete
 be specified in bytes with optional scale suffix [kKmMgG].  The default huge
 page size may be selected with the "default_hugepagesz=<size>" boot parameter.
 
-/proc/sys/vm/nr_hugepages indicates the current number of configured [default
-size] hugetlb pages in the kernel.  Super user can dynamically request more
-(or free some pre-configured) huge pages.
-
-Use the following command to dynamically allocate/deallocate default sized
-huge pages:
+When multiple huge page sizes are supported, /proc/sys/vm/nr_hugepages
+indicates the current number of pre-allocated huge pages of the default size.
+Thus, one can use the following command to dynamically allocate/deallocate
+default sized persistent huge pages:
 
 	echo 20 > /proc/sys/vm/nr_hugepages
 
-This command will try to configure 20 default sized huge pages in the system.
+This command will try to adjust the number of default sized huge pages in the
+huge page pool to 20, allocating or freeing huge pages, as required.
+
 On a NUMA platform, the kernel will attempt to distribute the huge page pool
-over the all on-line nodes.  These huge pages, allocated when nr_hugepages
-is increased, are called "persistent huge pages".
+over the all the nodes specified by the NUMA memory policy of the task that
+modifies nr_hugepages that contain sufficient available contiguous memory.
+These nodes are called the huge pages "allowed nodes".  The default for the
+huge pages allowed nodes--when the task has default memory policy--is all
+on-line nodes.  See the discussion below of the interaction of task memory
+policy, cpusets and persistent huge page allocation and freeing.
 
 The success or failure of huge page allocation depends on the amount of
 physically contiguous memory that is preset in system at the time of the
@@ -101,11 +102,11 @@ some nodes in a NUMA system, it will att
 allocating extra pages on other nodes with sufficient available contiguous
 memory, if any.
 
-System administrators may want to put this command in one of the local rc init
-files.  This will enable the kernel to request huge pages early in the boot
-process when the possibility of getting physical contiguous pages is still
-very high.  Administrators can verify the number of huge pages actually
-allocated by checking the sysctl or meminfo.  To check the per node
+System administrators may want to put this command in one of the local rc
+init files.  This will enable the kernel to preallocate huge pages early in
+the boot process when the possibility of getting physical contiguous pages
+is still very high.  Administrators can verify the number of huge pages
+actually allocated by checking the sysctl or meminfo.  To check the per node
 distribution of huge pages in a NUMA system, use:
 
 	cat /sys/devices/system/node/node*/meminfo | fgrep Huge
@@ -113,39 +114,40 @@ distribution of huge pages in a NUMA sys
 /proc/sys/vm/nr_overcommit_hugepages specifies how large the pool of
 huge pages can grow, if more huge pages than /proc/sys/vm/nr_hugepages are
 requested by applications.  Writing any non-zero value into this file
-indicates that the hugetlb subsystem is allowed to try to obtain "surplus"
-huge pages from the buddy allocator, when the normal pool is exhausted. As
-these surplus huge pages go out of use, they are freed back to the buddy
-allocator.
+indicates that the hugetlb subsystem is allowed to try to obtain that
+number of "surplus" huge pages from the kernel's normal page pool, when the
+persistent huge page pool is exhausted. As these surplus huge pages become
+unused, they are freed back to the kernel's normal page pool.
 
-When increasing the huge page pool size via nr_hugepages, any surplus
+When increasing the huge page pool size via nr_hugepages, any existing surplus
 pages will first be promoted to persistent huge pages.  Then, additional
 huge pages will be allocated, if necessary and if possible, to fulfill
-the new huge page pool size.
+the new persistent huge page pool size.
 
 The administrator may shrink the pool of preallocated huge pages for
 the default huge page size by setting the nr_hugepages sysctl to a
 smaller value.  The kernel will attempt to balance the freeing of huge pages
-across all on-line nodes.  Any free huge pages on the selected nodes will
-be freed back to the buddy allocator.
-
-Caveat: Shrinking the pool via nr_hugepages such that it becomes less
-than the number of huge pages in use will convert the balance to surplus
-huge pages even if it would exceed the overcommit value.  As long as
-this condition holds, however, no more surplus huge pages will be
-allowed on the system until one of the two sysctls are increased
-sufficiently, or the surplus huge pages go out of use and are freed.
+across all nodes in the memory policy of the task modifying nr_hugepages.
+Any free huge pages on the selected nodes will be freed back to the kernel's
+normal page pool.
+
+Caveat: Shrinking the persistent huge page pool via nr_hugepages such that
+it becomes less than the number of huge pages in use will convert the balance
+of the in-use huge pages to surplus huge pages.  This will occur even if
+the number of surplus pages it would exceed the overcommit value.  As long as
+this condition holds--that is, until nr_hugepages+nr_overcommit_hugepages is
+increased sufficiently, or the surplus huge pages go out of use and are freed--
+no more surplus huge pages will be allowed to be allocated.
 
 With support for multiple huge page pools at run-time available, much of
-the huge page userspace interface has been duplicated in sysfs. The above
-information applies to the default huge page size which will be
-controlled by the /proc interfaces for backwards compatibility. The root
-huge page control directory in sysfs is:
+the huge page userspace interface in /proc/sys/vm has been duplicated in sysfs.
+The /proc interfaces discussed above have been retained for backwards
+compatibility. The root huge page control directory in sysfs is:
 
 	/sys/kernel/mm/hugepages
 
 For each huge page size supported by the running kernel, a subdirectory
-will exist, of the form
+will exist, of the form:
 
 	hugepages-${size}kB
 
@@ -159,6 +161,70 @@ Inside each of these directories, the sa
 
 which function as described above for the default huge page-sized case.
 
+
+Interaction of Task Memory Policy with Huge Page Allocation/Freeing:
+
+Whether huge pages are allocated and freed via the /proc interface or
+the /sysfs interface, the NUMA nodes from which huge pages are allocated
+or freed are controlled by the NUMA memory policy of the task that modifies
+the nr_hugepages parameter.  [nr_overcommit_hugepages is a global limit.]
+
+The recommended method to allocate or free huge pages to/from the kernel
+huge page pool, using the nr_hugepages example above, is:
+
+    numactl --interleave <node-list> echo 20 >/proc/sys/vm/nr_hugepages.
+
+or, more succinctly:
+
+    numactl -m <node-list> echo 20 >/proc/sys/vm/nr_hugepages.
+
+This will allocate or free abs(20 - nr_hugepages) to or from the nodes
+specified in <node-list>, depending on whether nr_hugepages is initially
+less than or greater than 20, respectively.  No huge pages will be
+allocated nor freed on any node not included in the specified <node-list>.
+
+Any memory policy mode--bind, preferred, local or interleave--may be
+used.  The effect on persistent huge page allocation will be as follows:
+
+1) Regardless of mempolicy mode [see Documentation/vm/numa_memory_policy.txt],
+   persistent huge pages will be distributed across the node or nodes
+   specified in the mempolicy as if "interleave" had been specified.
+   However, if a node in the policy does not contain sufficient contiguous
+   memory for a huge page, the allocation will not "fallback" to the nearest
+   neighbor node with sufficient contiguous memory.  To do this would cause
+   undesirable imbalance in the distribution of the huge page pool, or
+   possibly, allocation of persistent huge pages on nodes not allowed by
+   the task's memory policy.
+
+2) One or more nodes may be specified with the bind or interleave policy.
+   If more than one node is specified with the preferred policy, only the
+   lowest numeric id will be used.  Local policy will select the node where
+   the task is running at the time the nodes_allowed mask is constructed.
+
+3) For local policy to be deterministic, the task must be bound to a cpu or
+   cpus in a single node.  Otherwise, the task could be migrated to some
+   other node at any time after launch and the resulting node will be
+   indeterminate.  Thus, local policy is not very useful for this purpose.
+   Any of the other mempolicy modes may be used to specify a single node.
+
+4) The nodes allowed mask will be derived from any non-default task mempolicy,
+   whether this policy was set explicitly by the task itself or one of its
+   ancestors, such as numactl.  This means that if the task is invoked from a
+   shell with non-default policy, that policy will be used.  One can specify a
+   node list of "all" with numactl --interleave or --membind [-m] to achieve
+   interleaving over all nodes in the system or cpuset.
+
+5) Any task mempolicy specifed--e.g., using numactl--will be constrained by
+   the resource limits of any cpuset in which the task runs.  Thus, there will
+   be no way for a task with non-default policy running in a cpuset with a
+   subset of the system nodes to allocate huge pages outside the cpuset
+   without first moving to a cpuset that contains all of the desired nodes.
+
+6) Hugepages allocated at boot time always use the node_online_map.
+
+
+Using Huge Pages:
+
 If the user applications are going to request huge pages using mmap system
 call, then it is required that system administrator mount a file system of
 type hugetlbfs:
@@ -204,9 +270,11 @@ mount of filesystem will be required for
  * requesting huge pages.
  *
  * For the ia64 architecture, the Linux kernel reserves Region number 4 for
- * huge pages.  That means the addresses starting with 0x800000... will need
- * to be specified.  Specifying a fixed address is not required on ppc64,
- * i386 or x86_64.
+ * huge pages.  That means that if one requires a fixed address, a huge page
+ * aligned address starting with 0x800000... will be required.  If a fixed
+ * address is not required, the kernel will select an address in the proper
+ * range.
+ * Other architectures, such as ppc64, i386 or x86_64 are not so constrained.
  *
  * Note: The default shared memory limit is quite low on many kernels,
  * you may need to increase it via:
@@ -235,14 +303,8 @@ mount of filesystem will be required for
 
 #define dprintf(x)  printf(x)
 
-/* Only ia64 requires this */
-#ifdef __ia64__
-#define ADDR (void *)(0x8000000000000000UL)
-#define SHMAT_FLAGS (SHM_RND)
-#else
-#define ADDR (void *)(0x0UL)
+#define ADDR (void *)(0x0UL)	/* let kernel choose address */
 #define SHMAT_FLAGS (0)
-#endif
 
 int main(void)
 {
@@ -300,10 +362,12 @@ int main(void)
  * example, the app is requesting memory of size 256MB that is backed by
  * huge pages.
  *
- * For ia64 architecture, Linux kernel reserves Region number 4 for huge pages.
- * That means the addresses starting with 0x800000... will need to be
- * specified.  Specifying a fixed address is not required on ppc64, i386
- * or x86_64.
+ * For the ia64 architecture, the Linux kernel reserves Region number 4 for
+ * huge pages.  That means that if one requires a fixed address, a huge page
+ * aligned address starting with 0x800000... will be required.  If a fixed
+ * address is not required, the kernel will select an address in the proper
+ * range.
+ * Other architectures, such as ppc64, i386 or x86_64 are not so constrained.
  */
 #include <stdlib.h>
 #include <stdio.h>
@@ -315,14 +379,8 @@ int main(void)
 #define LENGTH (256UL*1024*1024)
 #define PROTECTION (PROT_READ | PROT_WRITE)
 
-/* Only ia64 requires this */
-#ifdef __ia64__
-#define ADDR (void *)(0x8000000000000000UL)
-#define FLAGS (MAP_SHARED | MAP_FIXED)
-#else
-#define ADDR (void *)(0x0UL)
+#define ADDR (void *)(0x0UL)	/* let kernel choose address */
 #define FLAGS (MAP_SHARED)
-#endif
 
 void check_bytes(char *addr)
 {