linux-kernel - Re: [PATCH v3] mm/hugetlb: fix memory offline with hugepage size

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Date:   Thu, 22 Sep 2016 11:12:06 -0700
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     Gerald Schaefer <gerald.schaefer@...ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Michal Hocko <mhocko@...nel.org>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        Hillf Danton <hillf.zj@...baba-inc.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.vnet.ibm.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Rui Teng <rui.teng@...ux.vnet.ibm.com>
Subject: Re: [PATCH v3] mm/hugetlb: fix memory offline with hugepage size >
 memory block size

On 09/22/2016 09:29 AM, Gerald Schaefer wrote:
>  static void dissolve_free_huge_page(struct page *page)
>  {
> +	struct page *head = compound_head(page);
> +	struct hstate *h = page_hstate(head);
> +	int nid = page_to_nid(head);
> +
>  	spin_lock(&hugetlb_lock);
> -	if (PageHuge(page) && !page_count(page)) {
> -		struct hstate *h = page_hstate(page);
> -		int nid = page_to_nid(page);
> -		list_del(&page->lru);
> -		h->free_huge_pages--;
> -		h->free_huge_pages_node[nid]--;
> -		h->max_huge_pages--;
> -		update_and_free_page(h, page);
> -	}
> +	list_del(&head->lru);
> +	h->free_huge_pages--;
> +	h->free_huge_pages_node[nid]--;
> +	h->max_huge_pages--;
> +	update_and_free_page(h, head);
>  	spin_unlock(&hugetlb_lock);
>  }

Do you need to revalidate anything once you acquire the lock?  Can this,
for instance, race with another thread doing vm.nr_hugepages=0?  Or a
thread faulting in and allocating the large page that's being dissolved?