Re: [PATCH 02/10] hugetlb: add allocate function for hugepage migration

[Mel Gorman <mel@csn.ul.ie>]

On Wed, Sep 08, 2010 at 10:19:33AM +0900, Naoya Horiguchi wrote:
> We can't use existing hugepage allocation functions to allocate hugepage
> for page migration, because page migration can happen asynchronously with
> the running processes and page migration users should call the allocation
> function with physical addresses (not virtual addresses) as arguments.
> 
> ChangeLog since v3:
> - unify alloc_buddy_huge_page() and alloc_buddy_huge_page_node()
> 
> ChangeLog since v2:
> - remove unnecessary get/put_mems_allowed() (thanks to David Rientjes)
> 
> ChangeLog since v1:
> - add comment on top of alloc_huge_page_no_vma()
> 
> Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
> ---
>  include/linux/hugetlb.h |    3 ++
>  mm/hugetlb.c            |   79 ++++++++++++++++++++++++++++++++---------------
>  2 files changed, 57 insertions(+), 25 deletions(-)
> 
> diff --git v2.6.36-rc2/include/linux/hugetlb.h v2.6.36-rc2/include/linux/hugetlb.h
> index f479700..0b73c53 100644
> --- v2.6.36-rc2/include/linux/hugetlb.h
> +++ v2.6.36-rc2/include/linux/hugetlb.h
> @@ -228,6 +228,8 @@ struct huge_bootmem_page {
>  	struct hstate *hstate;
>  };
>  
> +struct page *alloc_huge_page_node(struct hstate *h, int nid);
> +
>  /* arch callback */
>  int __init alloc_bootmem_huge_page(struct hstate *h);
>  
> @@ -303,6 +305,7 @@ static inline struct hstate *page_hstate(struct page *page)
>  
>  #else
>  struct hstate {};
> +#define alloc_huge_page_node(h, nid) NULL
>  #define alloc_bootmem_huge_page(h) NULL
>  #define hstate_file(f) NULL
>  #define hstate_vma(v) NULL
> diff --git v2.6.36-rc2/mm/hugetlb.c v2.6.36-rc2/mm/hugetlb.c
> index 6871b41..f526228 100644
> --- v2.6.36-rc2/mm/hugetlb.c
> +++ v2.6.36-rc2/mm/hugetlb.c
> @@ -466,11 +466,23 @@ static void enqueue_huge_page(struct hstate *h, struct page *page)
>  	h->free_huge_pages_node[nid]++;
>  }
>  
> +static struct page *dequeue_huge_page_node(struct hstate *h, int nid)
> +{
> +	struct page *page;
> +
> +	if (list_empty(&h->hugepage_freelists[nid]))
> +		return NULL;
> +	page = list_entry(h->hugepage_freelists[nid].next, struct page, lru);
> +	list_del(&page->lru);
> +	h->free_huge_pages--;
> +	h->free_huge_pages_node[nid]--;
> +	return page;
> +}
> +

Ok, this is fine because all you are doing is splitting
dequeue_huge_page_vma()

>  static struct page *dequeue_huge_page_vma(struct hstate *h,
>  				struct vm_area_struct *vma,
>  				unsigned long address, int avoid_reserve)
>  {
> -	int nid;
>  	struct page *page = NULL;
>  	struct mempolicy *mpol;
>  	nodemask_t *nodemask;
> @@ -496,19 +508,13 @@ static struct page *dequeue_huge_page_vma(struct hstate *h,
>  
>  	for_each_zone_zonelist_nodemask(zone, z, zonelist,
>  						MAX_NR_ZONES - 1, nodemask) {
> -		nid = zone_to_nid(zone);
> -		if (cpuset_zone_allowed_softwall(zone, htlb_alloc_mask) &&
> -		    !list_empty(&h->hugepage_freelists[nid])) {
> -			page = list_entry(h->hugepage_freelists[nid].next,
> -					  struct page, lru);
> -			list_del(&page->lru);
> -			h->free_huge_pages--;
> -			h->free_huge_pages_node[nid]--;
> -
> -			if (!avoid_reserve)
> -				decrement_hugepage_resv_vma(h, vma);
> -
> -			break;
> +		if (cpuset_zone_allowed_softwall(zone, htlb_alloc_mask)) {
> +			page = dequeue_huge_page_node(h, zone_to_nid(zone));
> +			if (page) {
> +				if (!avoid_reserve)
> +					decrement_hugepage_resv_vma(h, vma);
> +				break;
> +			}
>  		}
>  	}

This looks functionally equivalent so no problems there.

>  err:
> @@ -770,11 +776,10 @@ static int free_pool_huge_page(struct hstate *h, nodemask_t *nodes_allowed,
>  	return ret;
>  }
>  
> -static struct page *alloc_buddy_huge_page(struct hstate *h,
> -			struct vm_area_struct *vma, unsigned long address)
> +static struct page *alloc_buddy_huge_page(struct hstate *h, int nid)
>  {
>  	struct page *page;
> -	unsigned int nid;
> +	unsigned int r_nid;
>  

Why the rename, just to avoid changing the value of a function parameter?

>  	if (h->order >= MAX_ORDER)
>  		return NULL;
> @@ -812,9 +817,14 @@ static struct page *alloc_buddy_huge_page(struct hstate *h,
>  	}
>  	spin_unlock(&hugetlb_lock);
>  
> -	page = alloc_pages(htlb_alloc_mask|__GFP_COMP|
> -					__GFP_REPEAT|__GFP_NOWARN,
> -					huge_page_order(h));
> +	if (nid == NUMA_NO_NODE)
> +		page = alloc_pages(htlb_alloc_mask|__GFP_COMP|
> +				   __GFP_REPEAT|__GFP_NOWARN,
> +				   huge_page_order(h));
> +	else
> +		page = alloc_pages_exact_node(nid,
> +			htlb_alloc_mask|__GFP_COMP|__GFP_THISNODE|
> +			__GFP_REPEAT|__GFP_NOWARN, huge_page_order(h));
>  

Why not just call alloc_pages_node()?

>  	if (page && arch_prepare_hugepage(page)) {
>  		__free_pages(page, huge_page_order(h));
> @@ -829,13 +839,13 @@ static struct page *alloc_buddy_huge_page(struct hstate *h,
>  		 */
>  		put_page_testzero(page);
>  		VM_BUG_ON(page_count(page));
> -		nid = page_to_nid(page);
> +		r_nid = page_to_nid(page);
>  		set_compound_page_dtor(page, free_huge_page);
>  		/*
>  		 * We incremented the global counters already
>  		 */
> -		h->nr_huge_pages_node[nid]++;
> -		h->surplus_huge_pages_node[nid]++;
> +		h->nr_huge_pages_node[r_nid]++;
> +		h->surplus_huge_pages_node[r_nid]++;
>  		__count_vm_event(HTLB_BUDDY_PGALLOC);
>  	} else {
>  		h->nr_huge_pages--;
> @@ -848,6 +858,25 @@ static struct page *alloc_buddy_huge_page(struct hstate *h,
>  }
>  
>  /*
> + * This allocation function is useful in the context where vma is irrelevant.
> + * E.g. soft-offlining uses this function because it only cares physical
> + * address of error page.
> + */
> +struct page *alloc_huge_page_node(struct hstate *h, int nid)
> +{
> +	struct page *page;
> +
> +	spin_lock(&hugetlb_lock);
> +	page = dequeue_huge_page_node(h, nid);
> +	spin_unlock(&hugetlb_lock);
> +
> +	if (!page)
> +		page = alloc_buddy_huge_page(h, nid);
> +
> +	return page;
> +}
> +
> +/*
>   * Increase the hugetlb pool such that it can accomodate a reservation
>   * of size 'delta'.
>   */
> @@ -871,7 +900,7 @@ static int gather_surplus_pages(struct hstate *h, int delta)
>  retry:
>  	spin_unlock(&hugetlb_lock);
>  	for (i = 0; i < needed; i++) {
> -		page = alloc_buddy_huge_page(h, NULL, 0);
> +		page = alloc_buddy_huge_page(h, NUMA_NO_NODE);
>  		if (!page) {
>  			/*
>  			 * We were not able to allocate enough pages to
> @@ -1052,7 +1081,7 @@ static struct page *alloc_huge_page(struct vm_area_struct *vma,
>  	spin_unlock(&hugetlb_lock);
>  
>  	if (!page) {
> -		page = alloc_buddy_huge_page(h, vma, addr);
> +		page = alloc_buddy_huge_page(h, NUMA_NO_NODE);
>  		if (!page) {
>  			hugetlb_put_quota(inode->i_mapping, chg);
>  			return ERR_PTR(-VM_FAULT_SIGBUS);

Mostly it looks ok, the only snag I see is the why you didn't use
alloc_pages_node().

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