linux-kernel - Re: [PATCH 1/3] HWPOISON, hugetlbfs: fix warning on freeing hwpoisoned hugepage

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Message-Id: <20121206143652.29c4922f.akpm@linux-foundation.org>
Date:	Thu, 6 Dec 2012 14:36:52 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Cc:	Andi Kleen <andi.kleen@...el.com>, Tony Luck <tony.luck@...el.com>,
	Wu Fengguang <fengguang.wu@...el.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 1/3] HWPOISON, hugetlbfs: fix warning on freeing
 hwpoisoned hugepage

On Wed,  5 Dec 2012 16:47:36 -0500
Naoya Horiguchi <n-horiguchi@...jp.nec.com> wrote:

> This patch fixes the warning from __list_del_entry() which is triggered
> when a process tries to do free_huge_page() for a hwpoisoned hugepage.
> 
> Originally, page->lru of hugetlbfs head page was dangling when the
> hugepage was in use. This behavior has changed by commit 0edaecfab218d7
> ("hugetlb: add a list for tracking in-use HugeTLB pages"), where hugepages
> in use are linked to hugepage_activelist. HWpoisoned hugepages should not
> be charged to any process, so we introduce another list to link hwpoisoned
> hugepages.
> 
> ...
>
> --- v3.7-rc8.orig/include/linux/hugetlb.h
> +++ v3.7-rc8/include/linux/hugetlb.h
> @@ -230,6 +230,9 @@ struct hstate {
>  	unsigned long nr_overcommit_huge_pages;
>  	struct list_head hugepage_activelist;
>  	struct list_head hugepage_freelists[MAX_NUMNODES];
> +#ifdef CONFIG_MEMORY_FAILURE
> +	struct list_head hugepage_hwpoisonedlist;
> +#endif
>  	unsigned int nr_huge_pages_node[MAX_NUMNODES];
>  	unsigned int free_huge_pages_node[MAX_NUMNODES];
>  	unsigned int surplus_huge_pages_node[MAX_NUMNODES];
> diff --git v3.7-rc8.orig/mm/hugetlb.c v3.7-rc8/mm/hugetlb.c
> index 59a0059..e61a749 100644
> --- v3.7-rc8.orig/mm/hugetlb.c
> +++ v3.7-rc8/mm/hugetlb.c
> @@ -1939,6 +1939,7 @@ void __init hugetlb_add_hstate(unsigned order)
>  	for (i = 0; i < MAX_NUMNODES; ++i)
>  		INIT_LIST_HEAD(&h->hugepage_freelists[i]);
>  	INIT_LIST_HEAD(&h->hugepage_activelist);
> +	INIT_LIST_HEAD(&h->hugepage_hwpoisonedlist);
>  	h->next_nid_to_alloc = first_node(node_states[N_HIGH_MEMORY]);
>  	h->next_nid_to_free = first_node(node_states[N_HIGH_MEMORY]);
>  	snprintf(h->name, HSTATE_NAME_LEN, "hugepages-%lukB",
> @@ -3170,7 +3171,7 @@ int dequeue_hwpoisoned_huge_page(struct page *hpage)
>  
>  	spin_lock(&hugetlb_lock);
>  	if (is_hugepage_on_freelist(hpage)) {
> -		list_del(&hpage->lru);
> +		list_move(&hpage->lru, &h->hugepage_hwpoisonedlist);
>  		set_page_refcounted(hpage);
>  		h->free_huge_pages--;
>  		h->free_huge_pages_node[nid]--;

Do we actually need to new list?  We could use list_del_init() to leave
the page's list_head pointing at itself.  In this state, it is its own
list_head and further list_del()s are a no-op.

I don't know whether this would trigger list-debug warnings.
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