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

[Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>]

On Thu, Dec 06, 2012 at 02:36:52PM -0800, Andrew Morton wrote:
> On Wed,  5 Dec 2012 16:47:36 -0500
> Naoya Horiguchi <n-horiguchi@ah.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.

OK, it's better, thanks.

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

I tested your idea (with attached patch) and confirmed that
we never get the warnings.

Thanks,
Naoya
---
From: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Date: Thu, 6 Dec 2012 20:54:30 -0500
Subject: [PATCH v2] HWPOISON, hugetlbfs: fix warning on freeing hwpoisoned
 hugepage

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.

ChangeLog v2:
 - simply use list_del_init instead of introducing new hugepage list

Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
---
 mm/hugetlb.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 59a0059..9308752 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -3170,7 +3170,7 @@ int dequeue_hwpoisoned_huge_page(struct page *hpage)
 
 	spin_lock(&hugetlb_lock);
 	if (is_hugepage_on_freelist(hpage)) {
-		list_del(&hpage->lru);
+		list_del_init(&hpage->lru);
 		set_page_refcounted(hpage);
 		h->free_huge_pages--;
 		h->free_huge_pages_node[nid]--;
-- 
1.7.11.7

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