Re: [PATCH v5 15/21] mm/hugetlb: Set the PageHWPoison to the raw error page

[Michal Hocko]

On Fri 20-11-20 14:43:19, Muchun Song wrote:
> Because we reuse the first tail page, if we set PageHWPosion on a
> tail page. It indicates that we may set PageHWPoison on a series
> of pages. So we can use the head[4].mapping to record the real
> error page index and set the raw error page PageHWPoison later.

This really begs more explanation. Maybe I misremember but If there
is a HWPoison hole in a hugepage then the whole page is demolished, no?
If that is the case then why do we care about tail pages?
 
> Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
> ---
>  mm/hugetlb.c         | 11 +++--------
>  mm/hugetlb_vmemmap.h | 39 +++++++++++++++++++++++++++++++++++++++
>  2 files changed, 42 insertions(+), 8 deletions(-)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 055604d07046..b853aacd5c16 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1383,6 +1383,7 @@ static void __free_hugepage(struct hstate *h, struct page *page)
>  	int i;
>  
>  	alloc_huge_page_vmemmap(h, page);
> +	subpage_hwpoison_deliver(page);
>  
>  	for (i = 0; i < pages_per_huge_page(h); i++) {
>  		page[i].flags &= ~(1 << PG_locked | 1 << PG_error |
> @@ -1944,14 +1945,8 @@ int dissolve_free_huge_page(struct page *page)
>  		int nid = page_to_nid(head);
>  		if (h->free_huge_pages - h->resv_huge_pages == 0)
>  			goto out;
> -		/*
> -		 * Move PageHWPoison flag from head page to the raw error page,
> -		 * which makes any subpages rather than the error page reusable.
> -		 */
> -		if (PageHWPoison(head) && page != head) {
> -			SetPageHWPoison(page);
> -			ClearPageHWPoison(head);
> -		}
> +
> +		set_subpage_hwpoison(head, page);
>  		list_del(&head->lru);
>  		h->free_huge_pages--;
>  		h->free_huge_pages_node[nid]--;
> diff --git a/mm/hugetlb_vmemmap.h b/mm/hugetlb_vmemmap.h
> index 779d3cb9333f..65e94436ffff 100644
> --- a/mm/hugetlb_vmemmap.h
> +++ b/mm/hugetlb_vmemmap.h
> @@ -20,6 +20,29 @@ void __init gather_vmemmap_pgtable_init(struct huge_bootmem_page *m,
>  void alloc_huge_page_vmemmap(struct hstate *h, struct page *head);
>  void free_huge_page_vmemmap(struct hstate *h, struct page *head);
>  
> +static inline void subpage_hwpoison_deliver(struct page *head)
> +{
> +	struct page *page = head;
> +
> +	if (PageHWPoison(head))
> +		page = head + page_private(head + 4);
> +
> +	/*
> +	 * Move PageHWPoison flag from head page to the raw error page,
> +	 * which makes any subpages rather than the error page reusable.
> +	 */
> +	if (page != head) {
> +		SetPageHWPoison(page);
> +		ClearPageHWPoison(head);
> +	}
> +}
> +
> +static inline void set_subpage_hwpoison(struct page *head, struct page *page)
> +{
> +	if (PageHWPoison(head))
> +		set_page_private(head + 4, page - head);
> +}
> +
>  static inline unsigned int free_vmemmap_pages_per_hpage(struct hstate *h)
>  {
>  	return h->nr_free_vmemmap_pages;
> @@ -56,6 +79,22 @@ static inline void free_huge_page_vmemmap(struct hstate *h, struct page *head)
>  {
>  }
>  
> +static inline void subpage_hwpoison_deliver(struct page *head)
> +{
> +}
> +
> +static inline void set_subpage_hwpoison(struct page *head, struct page *page)
> +{
> +	/*
> +	 * Move PageHWPoison flag from head page to the raw error page,
> +	 * which makes any subpages rather than the error page reusable.
> +	 */
> +	if (PageHWPoison(head) && page != head) {
> +		SetPageHWPoison(page);
> +		ClearPageHWPoison(head);
> +	}
> +}
> +
>  static inline unsigned int free_vmemmap_pages_per_hpage(struct hstate *h)
>  {
>  	return 0;
> -- 
> 2.11.0
> 

-- 
Michal Hocko
SUSE Labs