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

[Lee Schermerhorn <Lee.Schermerhorn@hp.com>]

On Wed, 2009-07-01 at 13:38 +0100, Mel Gorman wrote:
> On Tue, Jun 30, 2009 at 11:47:24AM -0400, Lee Schermerhorn wrote:
> > [RFC 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	2009-06-29 17:35:11.000000000 -0400
> > +++ linux-2.6.31-rc1-mmotm-090625-1549/mm/hugetlb.c	2009-06-29 23:01:01.000000000 -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;
> > @@ -717,7 +727,7 @@ 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;
> > @@ -919,7 +929,7 @@ 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;
> >  	}
> >  }
> > @@ -1032,6 +1042,7 @@ 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
> > @@ -1041,7 +1052,6 @@ int __weak alloc_bootmem_huge_page(struc
> >  			m = addr;
> >  			goto found;
> >  		}
> > -		hstate_next_node_to_alloc(h);
> >  		nr_nodes--;
> 
> 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.
> 
> This could be a seperate patch just for consideration in isolation but I
> for one have no problem with it. If you split out this patch, feel free
> to add an Ack from me.

OK.  If this series doesn't fly--e.g., we take another approach--I will
definitely split this out.  If Andrew wants it separate for the change
log, I can do that as well.

> 
> >  	}
> >  	return 0;
> > @@ -1085,7 +1095,7 @@ 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;
> > @@ -1160,7 +1170,8 @@ 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;
> > @@ -1176,7 +1187,7 @@ 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
> >  			 */
> > @@ -1184,7 +1195,7 @@ 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
> >  			 */
> > @@ -1223,7 +1234,7 @@ 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;
> >  	}
> >  
> > @@ -1234,7 +1245,7 @@ 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;
> > @@ -1260,11 +1271,11 @@ 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:
> > 
> 
> Otherwise, this looks like a relatively straight-forward conversion to
> having nodemask awareness. I'd expect no behavioural changes from this
> patch at all so

Yeah, that was the idea.  This one should preserve the existing
behavior, but prep for the next one.

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

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