linux-kernel - Re: [RFC PATCH v1 1/4] mm, hwpoison, hugetlb: introduce SUBPAGE_INDEX

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Message-ID: <5b956156-887b-1d91-7831-28a66db53c6a@huawei.com>
Date:   Wed, 27 Apr 2022 15:11:31 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     Naoya Horiguchi <naoya.horiguchi@...ux.dev>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...hat.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Yang Shi <shy828301@...il.com>,
        Oscar Salvador <osalvador@...e.de>,
        Muchun Song <songmuchun@...edance.com>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        <linux-kernel@...r.kernel.org>, Linux-MM <linux-mm@...ck.org>
Subject: Re: [RFC PATCH v1 1/4] mm, hwpoison, hugetlb: introduce
 SUBPAGE_INDEX_HWPOISON to save raw error page

On 2022/4/27 12:28, Naoya Horiguchi wrote:
> From: Naoya Horiguchi <naoya.horiguchi@....com>
> 
> When handling memory error on a hugetlb page, the error handler tries to
> dissolve and turn it into 4kB pages.  If it's successfully dissolved,
> PageHWPoison flag is moved to the raw error page, so but that's all

s/so but/so/

> right.  However, dissolve sometimes fails, then the error page is left
> as hwpoisoned hugepage. It's useful if we can retry to dissolve it to
> save healthy pages, but that's not possible now because the information
> about where the raw error page is lost.
> 
> Use the private field of a tail page to keep that information.  The code

Only one raw error page is saved now. Should this be ok? I think so as memory
failure should be rare anyway?

> path of shrinking hugepage pool used this info to try delayed dissolve.
> 
> Signed-off-by: Naoya Horiguchi <naoya.horiguchi@....com>
> ---
>  include/linux/hugetlb.h | 24 ++++++++++++++++++++++++
>  mm/hugetlb.c            |  9 +++++++++
>  mm/memory-failure.c     |  2 ++
>  3 files changed, 35 insertions(+)
> 
> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> index ac2a1d758a80..689e69cb556b 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -42,6 +42,9 @@ enum {
>  	SUBPAGE_INDEX_CGROUP,		/* reuse page->private */
>  	SUBPAGE_INDEX_CGROUP_RSVD,	/* reuse page->private */
>  	__MAX_CGROUP_SUBPAGE_INDEX = SUBPAGE_INDEX_CGROUP_RSVD,
> +#endif
> +#ifdef CONFIG_CGROUP_HUGETLB
> +	SUBPAGE_INDEX_HWPOISON,
>  #endif

Do we rely on the CONFIG_CGROUP_HUGETLB to store the raw error page?

>  	__NR_USED_SUBPAGE,
>  };
> @@ -784,6 +787,27 @@ extern int dissolve_free_huge_page(struct page *page);
>  extern int dissolve_free_huge_pages(unsigned long start_pfn,
>  				    unsigned long end_pfn);
>  
> +#ifdef CONFIG_MEMORY_FAILURE
> +/*
> + * pointer to raw error page is located in hpage[SUBPAGE_INDEX_HWPOISON].private
> + */
> +static inline struct page *hugetlb_page_hwpoison(struct page *hpage)
> +{
> +	return (void *)page_private(hpage + SUBPAGE_INDEX_HWPOISON);
> +}
> +
> +static inline void hugetlb_set_page_hwpoison(struct page *hpage,
> +					struct page *page)
> +{
> +	set_page_private(hpage + SUBPAGE_INDEX_HWPOISON, (unsigned long)page);
> +}
> +#else
> +static inline struct page *hugetlb_page_hwpoison(struct page *hpage)
> +{
> +	return NULL;
> +}
> +#endif
> +
>  #ifdef CONFIG_ARCH_ENABLE_HUGEPAGE_MIGRATION
>  #ifndef arch_hugetlb_migration_supported
>  static inline bool arch_hugetlb_migration_supported(struct hstate *h)
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index f8e048b939c7..6867ea8345d1 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1547,6 +1547,15 @@ static void __update_and_free_page(struct hstate *h, struct page *page)
>  		return;
>  	}
>  
> +	if (unlikely(PageHWPoison(page))) {
> +		struct page *raw_error = hugetlb_page_hwpoison(page);
> +
> +		if (raw_error && raw_error != page) {
> +			SetPageHWPoison(raw_error);
> +			ClearPageHWPoison(page);
> +		}
> +	}
> +
>  	for (i = 0; i < pages_per_huge_page(h);
>  	     i++, subpage = mem_map_next(subpage, page, i)) {
>  		subpage->flags &= ~(1 << PG_locked | 1 << PG_error |
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 3e36fc19c4d1..73948a00ad4a 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -1535,6 +1535,8 @@ int __get_huge_page_for_hwpoison(unsigned long pfn, int flags)
>  		goto out;
>  	}
>  
> +	hugetlb_set_page_hwpoison(head, page);
> +
>  	return ret;
>  out:
>  	if (count_increased)
> 

This patch looks good to me. I will learn this series more when I get more time.
Many thanks for your hard work! :)