Re: [PATCH 5/6] mm, hugetlb: further simplify hugetlb allocation API

[Dan Rue]

On Wed, Jan 03, 2018 at 10:32:12AM +0100, Michal Hocko wrote:
> From: Michal Hocko <mhocko@xxxxxxxx>
> 
> Hugetlb allocator has several layer of allocation functions depending
> and the purpose of the allocation. There are two allocators depending
> on whether the page can be allocated from the page allocator or we need
> a contiguous allocator. This is currently opencoded in alloc_fresh_huge_page
> which is the only path that might allocate giga pages which require the
> later allocator. Create alloc_fresh_huge_page which hides this
> implementation detail and use it in all callers which hardcoded the
> buddy allocator path (__hugetlb_alloc_buddy_huge_page). This shouldn't
> introduce any funtional change because both migration and surplus
> allocators exlude giga pages explicitly.
> 
> While we are at it let's do some renaming. The current scheme is not
> consistent and overly painfull to read and understand. Get rid of prefix
> underscores from most functions. There is no real reason to make names
> longer.
> * alloc_fresh_huge_page is the new layer to abstract underlying
>   allocator
> * __hugetlb_alloc_buddy_huge_page becomes shorter and neater
>   alloc_buddy_huge_page.
> * Former alloc_fresh_huge_page becomes alloc_pool_huge_page because we put
>   the new page directly to the pool
> * alloc_surplus_huge_page can drop the opencoded prep_new_huge_page code
>   as it uses alloc_fresh_huge_page now
> * others lose their excessive prefix underscores to make names shorter

Hi Michal -

We (Linaro) run the libhugetlbfs test suite continuously against
mainline and recently (Feb 1), the 'counters' test started failing on
with the following error:

    root@localhost:~# mount_point="/mnt/hugetlb/"
    root@localhost:~# echo 200 > /proc/sys/vm/nr_hugepages
    root@localhost:~# mkdir -p "${mount_point}"
    root@localhost:~# mount -t hugetlbfs hugetlbfs "${mount_point}"
    root@localhost:~# export LD_LIBRARY_PATH=/root/libhugetlbfs/libhugetlbfs-2.20/obj64
    root@localhost:~# /root/libhugetlbfs/libhugetlbfs-2.20/tests/obj64/counters
    Starting testcase "/root/libhugetlbfs/libhugetlbfs-2.20/tests/obj64/counters", pid 3319
    Base pool size: 0
    Clean...
    FAIL    Line 326: Bad HugePages_Total: expected 0, actual 1

Line 326 refers to the test source @
https://github.com/libhugetlbfs/libhugetlbfs/blob/master/tests/counters.c#L326

I bisected the failure to this commit. The problem is seen on multiple
architectures (tested x86-64 and arm64).

Thanks,
Dan

> 
> Reviewed-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> Reviewed-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
> Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
> ---
>  mm/hugetlb.c | 78 ++++++++++++++++++++++++++++++++----------------------------
>  1 file changed, 42 insertions(+), 36 deletions(-)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 7dc80cbe8e89..60acd3e93a95 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1378,7 +1378,7 @@ pgoff_t __basepage_index(struct page *page)
>  	return (index << compound_order(page_head)) + compound_idx;
>  }
>  
> -static struct page *__hugetlb_alloc_buddy_huge_page(struct hstate *h,
> +static struct page *alloc_buddy_huge_page(struct hstate *h,
>  		gfp_t gfp_mask, int nid, nodemask_t *nmask)
>  {
>  	int order = huge_page_order(h);
> @@ -1396,34 +1396,49 @@ static struct page *__hugetlb_alloc_buddy_huge_page(struct hstate *h,
>  	return page;
>  }
>  
> +/*
> + * Common helper to allocate a fresh hugetlb page. All specific allocators
> + * should use this function to get new hugetlb pages
> + */
> +static struct page *alloc_fresh_huge_page(struct hstate *h,
> +		gfp_t gfp_mask, int nid, nodemask_t *nmask)
> +{
> +	struct page *page;
> +
> +	if (hstate_is_gigantic(h))
> +		page = alloc_gigantic_page(h, gfp_mask, nid, nmask);
> +	else
> +		page = alloc_buddy_huge_page(h, gfp_mask,
> +				nid, nmask);
> +	if (!page)
> +		return NULL;
> +
> +	if (hstate_is_gigantic(h))
> +		prep_compound_gigantic_page(page, huge_page_order(h));
> +	prep_new_huge_page(h, page, page_to_nid(page));
> +
> +	return page;
> +}
> +
>  /*
>   * Allocates a fresh page to the hugetlb allocator pool in the node interleaved
>   * manner.
>   */
> -static int alloc_fresh_huge_page(struct hstate *h, nodemask_t *nodes_allowed)
> +static int alloc_pool_huge_page(struct hstate *h, nodemask_t *nodes_allowed)
>  {
>  	struct page *page;
>  	int nr_nodes, node;
>  	gfp_t gfp_mask = htlb_alloc_mask(h) | __GFP_THISNODE;
>  
>  	for_each_node_mask_to_alloc(h, nr_nodes, node, nodes_allowed) {
> -		if (hstate_is_gigantic(h))
> -			page = alloc_gigantic_page(h, gfp_mask,
> -					node, nodes_allowed);
> -		else
> -			page = __hugetlb_alloc_buddy_huge_page(h, gfp_mask,
> -					node, nodes_allowed);
> +		page = alloc_fresh_huge_page(h, gfp_mask, node, nodes_allowed);
>  		if (page)
>  			break;
> -
>  	}
>  
>  	if (!page)
>  		return 0;
>  
> -	if (hstate_is_gigantic(h))
> -		prep_compound_gigantic_page(page, huge_page_order(h));
> -	prep_new_huge_page(h, page, page_to_nid(page));
>  	put_page(page); /* free it into the hugepage allocator */
>  
>  	return 1;
> @@ -1537,7 +1552,7 @@ int dissolve_free_huge_pages(unsigned long start_pfn, unsigned long end_pfn)
>  /*
>   * Allocates a fresh surplus page from the page allocator.
>   */
> -static struct page *__alloc_surplus_huge_page(struct hstate *h, gfp_t gfp_mask,
> +static struct page *alloc_surplus_huge_page(struct hstate *h, gfp_t gfp_mask,
>  		int nid, nodemask_t *nmask)
>  {
>  	struct page *page = NULL;
> @@ -1550,7 +1565,7 @@ static struct page *__alloc_surplus_huge_page(struct hstate *h, gfp_t gfp_mask,
>  		goto out_unlock;
>  	spin_unlock(&hugetlb_lock);
>  
> -	page = __hugetlb_alloc_buddy_huge_page(h, gfp_mask, nid, nmask);
> +	page = alloc_fresh_huge_page(h, gfp_mask, nid, nmask);
>  	if (!page)
>  		goto out_unlock;
>  
> @@ -1567,16 +1582,8 @@ static struct page *__alloc_surplus_huge_page(struct hstate *h, gfp_t gfp_mask,
>  		put_page(page);
>  		page = NULL;
>  	} else {
> -		int r_nid;
> -
>  		h->surplus_huge_pages++;
> -		h->nr_huge_pages++;
> -		INIT_LIST_HEAD(&page->lru);
> -		r_nid = page_to_nid(page);
> -		set_compound_page_dtor(page, HUGETLB_PAGE_DTOR);
> -		set_hugetlb_cgroup(page, NULL);
> -		h->nr_huge_pages_node[r_nid]++;
> -		h->surplus_huge_pages_node[r_nid]++;
> +		h->nr_huge_pages_node[page_to_nid(page)]++;
>  	}
>  
>  out_unlock:
> @@ -1585,7 +1592,7 @@ static struct page *__alloc_surplus_huge_page(struct hstate *h, gfp_t gfp_mask,
>  	return page;
>  }
>  
> -static struct page *__alloc_migrate_huge_page(struct hstate *h, gfp_t gfp_mask,
> +static struct page *alloc_migrate_huge_page(struct hstate *h, gfp_t gfp_mask,
>  		int nid, nodemask_t *nmask)
>  {
>  	struct page *page;
> @@ -1593,7 +1600,7 @@ static struct page *__alloc_migrate_huge_page(struct hstate *h, gfp_t gfp_mask,
>  	if (hstate_is_gigantic(h))
>  		return NULL;
>  
> -	page = __hugetlb_alloc_buddy_huge_page(h, gfp_mask, nid, nmask);
> +	page = alloc_fresh_huge_page(h, gfp_mask, nid, nmask);
>  	if (!page)
>  		return NULL;
>  
> @@ -1601,7 +1608,6 @@ static struct page *__alloc_migrate_huge_page(struct hstate *h, gfp_t gfp_mask,
>  	 * We do not account these pages as surplus because they are only
>  	 * temporary and will be released properly on the last reference
>  	 */
> -	prep_new_huge_page(h, page, page_to_nid(page));
>  	SetPageHugeTemporary(page);
>  
>  	return page;
> @@ -1611,7 +1617,7 @@ static struct page *__alloc_migrate_huge_page(struct hstate *h, gfp_t gfp_mask,
>   * Use the VMA's mpolicy to allocate a huge page from the buddy.
>   */
>  static
> -struct page *__alloc_buddy_huge_page_with_mpol(struct hstate *h,
> +struct page *alloc_buddy_huge_page_with_mpol(struct hstate *h,
>  		struct vm_area_struct *vma, unsigned long addr)
>  {
>  	struct page *page;
> @@ -1621,7 +1627,7 @@ struct page *__alloc_buddy_huge_page_with_mpol(struct hstate *h,
>  	nodemask_t *nodemask;
>  
>  	nid = huge_node(vma, addr, gfp_mask, &mpol, &nodemask);
> -	page = __alloc_surplus_huge_page(h, gfp_mask, nid, nodemask);
> +	page = alloc_surplus_huge_page(h, gfp_mask, nid, nodemask);
>  	mpol_cond_put(mpol);
>  
>  	return page;
> @@ -1642,7 +1648,7 @@ struct page *alloc_huge_page_node(struct hstate *h, int nid)
>  	spin_unlock(&hugetlb_lock);
>  
>  	if (!page)
> -		page = __alloc_migrate_huge_page(h, gfp_mask, nid, NULL);
> +		page = alloc_migrate_huge_page(h, gfp_mask, nid, NULL);
>  
>  	return page;
>  }
> @@ -1665,7 +1671,7 @@ struct page *alloc_huge_page_nodemask(struct hstate *h, int preferred_nid,
>  	}
>  	spin_unlock(&hugetlb_lock);
>  
> -	return __alloc_migrate_huge_page(h, gfp_mask, preferred_nid, nmask);
> +	return alloc_migrate_huge_page(h, gfp_mask, preferred_nid, nmask);
>  }
>  
>  /*
> @@ -1693,7 +1699,7 @@ static int gather_surplus_pages(struct hstate *h, int delta)
>  retry:
>  	spin_unlock(&hugetlb_lock);
>  	for (i = 0; i < needed; i++) {
> -		page = __alloc_surplus_huge_page(h, htlb_alloc_mask(h),
> +		page = alloc_surplus_huge_page(h, htlb_alloc_mask(h),
>  				NUMA_NO_NODE, NULL);
>  		if (!page) {
>  			alloc_ok = false;
> @@ -2030,7 +2036,7 @@ struct page *alloc_huge_page(struct vm_area_struct *vma,
>  	page = dequeue_huge_page_vma(h, vma, addr, avoid_reserve, gbl_chg);
>  	if (!page) {
>  		spin_unlock(&hugetlb_lock);
> -		page = __alloc_buddy_huge_page_with_mpol(h, vma, addr);
> +		page = alloc_buddy_huge_page_with_mpol(h, vma, addr);
>  		if (!page)
>  			goto out_uncharge_cgroup;
>  		if (!avoid_reserve && vma_has_reserves(vma, gbl_chg)) {
> @@ -2170,7 +2176,7 @@ static void __init hugetlb_hstate_alloc_pages(struct hstate *h)
>  		if (hstate_is_gigantic(h)) {
>  			if (!alloc_bootmem_huge_page(h))
>  				break;
> -		} else if (!alloc_fresh_huge_page(h,
> +		} else if (!alloc_pool_huge_page(h,
>  					 &node_states[N_MEMORY]))
>  			break;
>  		cond_resched();
> @@ -2290,7 +2296,7 @@ static unsigned long set_max_huge_pages(struct hstate *h, unsigned long count,
>  	 * First take pages out of surplus state.  Then make up the
>  	 * remaining difference by allocating fresh huge pages.
>  	 *
> -	 * We might race with __alloc_surplus_huge_page() here and be unable
> +	 * We might race with alloc_surplus_huge_page() here and be unable
>  	 * to convert a surplus huge page to a normal huge page. That is
>  	 * not critical, though, it just means the overall size of the
>  	 * pool might be one hugepage larger than it needs to be, but
> @@ -2313,7 +2319,7 @@ static unsigned long set_max_huge_pages(struct hstate *h, unsigned long count,
>  		/* yield cpu to avoid soft lockup */
>  		cond_resched();
>  
> -		ret = alloc_fresh_huge_page(h, nodes_allowed);
> +		ret = alloc_pool_huge_page(h, nodes_allowed);
>  		spin_lock(&hugetlb_lock);
>  		if (!ret)
>  			goto out;
> @@ -2333,7 +2339,7 @@ static unsigned long set_max_huge_pages(struct hstate *h, unsigned long count,
>  	 * By placing pages into the surplus state independent of the
>  	 * overcommit value, we are allowing the surplus pool size to
>  	 * exceed overcommit. There are few sane options here. Since
> -	 * __alloc_surplus_huge_page() is checking the global counter,
> +	 * alloc_surplus_huge_page() is checking the global counter,
>  	 * though, we'll note that we're not allowed to exceed surplus
>  	 * and won't grow the pool anywhere else. Not until one of the
>  	 * sysctls are changed, or the surplus pages go out of use.
> -- 
> 2.15.1
>