linux-kernel - Re: [PATCH v2 13/20] mm, hugetlb: mm, hugetlb: unify chg and avoid_reserve to use

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Date:	Mon, 26 Aug 2013 18:39:35 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Rik van Riel <riel@...hat.com>, Mel Gorman <mgorman@...e.de>,
	Michal Hocko <mhocko@...e.cz>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Hugh Dickins <hughd@...gle.com>,
	Davidlohr Bueso <davidlohr.bueso@...com>,
	David Gibson <david@...son.dropbear.id.au>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Joonsoo Kim <js1304@...il.com>,
	Wanpeng Li <liwanp@...ux.vnet.ibm.com>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Hillf Danton <dhillf@...il.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH v2 13/20] mm, hugetlb: mm, hugetlb: unify chg and avoid_reserve to use_reserve

Joonsoo Kim <iamjoonsoo.kim@....com> writes:

> Currently, we have two variable to represent whether we can use reserved
> page or not, chg and avoid_reserve, respectively. With aggregating these,
> we can have more clean code. This makes no functinoal difference.
>
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 22ceb04..8dff972 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -531,8 +531,7 @@ static struct page *dequeue_huge_page_node(struct hstate *h, int nid)
>
>  static struct page *dequeue_huge_page_vma(struct hstate *h,
>  				struct vm_area_struct *vma,
> -				unsigned long address, int avoid_reserve,
> -				long chg)
> +				unsigned long address, bool use_reserve)
>  {
>  	struct page *page = NULL;
>  	struct mempolicy *mpol;
> @@ -546,12 +545,10 @@ static struct page *dequeue_huge_page_vma(struct hstate *h,
>  	 * A child process with MAP_PRIVATE mappings created by their parent
>  	 * have no page reserves. This check ensures that reservations are
>  	 * not "stolen". The child may still get SIGKILLed
> +	 * Or, when parent process do COW, we cannot use reserved page.
> +	 * In this case, ensure enough pages are in the pool.
>  	 */
> -	if (chg && h->free_huge_pages - h->resv_huge_pages == 0)
> -		return NULL;

This hunk would be much easier if you were changing. 

	if (!vma_has_reserves(vma) &&
			h->free_huge_pages - h->resv_huge_pages == 0)
		goto err;

ie, !vma_has_reserves(vma) == !use_reserve.

So may be a patch rearragment would help ?. But neverthless. 

Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>

> -
> -	/* If reserves cannot be used, ensure enough pages are in the pool */
> -	if (avoid_reserve && h->free_huge_pages - h->resv_huge_pages == 0)
> +	if (!use_reserve && h->free_huge_pages - h->resv_huge_pages == 0)
>  		return NULL;



>
>  retry_cpuset:
> @@ -564,9 +561,7 @@ retry_cpuset:
>  		if (cpuset_zone_allowed_softwall(zone, htlb_alloc_mask)) {
>  			page = dequeue_huge_page_node(h, zone_to_nid(zone));
>  			if (page) {
> -				if (avoid_reserve)
> -					break;
> -				if (chg)
> +				if (!use_reserve)
>  					break;
>
>  				SetPagePrivate(page);
> @@ -1121,6 +1116,7 @@ static struct page *alloc_huge_page(struct vm_area_struct *vma,
>  	struct hstate *h = hstate_vma(vma);
>  	struct page *page;
>  	long chg;
> +	bool use_reserve;
>  	int ret, idx;
>  	struct hugetlb_cgroup *h_cg;
>
> @@ -1136,18 +1132,19 @@ static struct page *alloc_huge_page(struct vm_area_struct *vma,
>  	chg = vma_needs_reservation(h, vma, addr);
>  	if (chg < 0)
>  		return ERR_PTR(-ENOMEM);
> -	if (chg || avoid_reserve)
> +	use_reserve = (!chg && !avoid_reserve);
> +	if (!use_reserve)
>  		if (hugepage_subpool_get_pages(spool, 1))
>  			return ERR_PTR(-ENOSPC);
>
>  	ret = hugetlb_cgroup_charge_cgroup(idx, pages_per_huge_page(h), &h_cg);
>  	if (ret) {
> -		if (chg || avoid_reserve)
> +		if (!use_reserve)
>  			hugepage_subpool_put_pages(spool, 1);
>  		return ERR_PTR(-ENOSPC);
>  	}
>  	spin_lock(&hugetlb_lock);
> -	page = dequeue_huge_page_vma(h, vma, addr, avoid_reserve, chg);
> +	page = dequeue_huge_page_vma(h, vma, addr, use_reserve);
>  	if (!page) {
>  		spin_unlock(&hugetlb_lock);
>  		page = alloc_buddy_huge_page(h, NUMA_NO_NODE);
> @@ -1155,7 +1152,7 @@ static struct page *alloc_huge_page(struct vm_area_struct *vma,
>  			hugetlb_cgroup_uncharge_cgroup(idx,
>  						       pages_per_huge_page(h),
>  						       h_cg);
> -			if (chg || avoid_reserve)
> +			if (!use_reserve)
>  				hugepage_subpool_put_pages(spool, 1);
>  			return ERR_PTR(-ENOSPC);
>  		}
> -- 
> 1.7.9.5

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