linux-kernel - Re: [PATCH mmotm v1] mm/hwpoison: disable pcp for page_handle

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Date:   Thu, 17 Jun 2021 14:21:29 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Naoya Horiguchi <nao.horiguchi@...il.com>, linux-mm@...ck.org
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Oscar Salvador <osalvador@...e.de>,
        Michal Hocko <mhocko@...e.com>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH mmotm v1] mm/hwpoison: disable pcp for
 page_handle_poison()

On 17.06.21 11:26, Naoya Horiguchi wrote:
> From: Naoya Horiguchi <naoya.horiguchi@....com>
> 
> Recent changes by patch "mm/page_alloc: allow high-order pages to be
> stored on the per-cpu lists" makes kernels determine whether to use pcp
> by pcp_allowed_order(), which breaks soft-offline for hugetlb pages.
> 
> Soft-offline dissolves a migration source page, then removes it from
> buddy free list, so it's assumed that any subpage of the soft-offlined
> hugepage are recognized as a buddy page just after returning from
> dissolve_free_huge_page().  pcp_allowed_order() returns true for
> hugetlb, so this assumption is no longer true.
> 
> So disable pcp during dissolve_free_huge_page() and
> take_page_off_buddy() to prevent soft-offlined hugepages from linking to
> pcp lists.  Soft-offline should not be common events so the impact on
> performance should be minimal.  And I think that the optimization of
> Mel's patch could benefit to hugetlb so zone_pcp_disable() is called
> only in hwpoison context.
> 
> Signed-off-by: Naoya Horiguchi <naoya.horiguchi@....com>
> ---
>   mm/memory-failure.c | 19 ++++++++++++++++---
>   1 file changed, 16 insertions(+), 3 deletions(-)
> 
> diff --git v5.13-rc6-mmotm-2021-06-15-20-24/mm/memory-failure.c v5.13-rc6-mmotm-2021-06-15-20-24_patched/mm/memory-failure.c
> index 1842822a10da..593079766655 100644
> --- v5.13-rc6-mmotm-2021-06-15-20-24/mm/memory-failure.c
> +++ v5.13-rc6-mmotm-2021-06-15-20-24_patched/mm/memory-failure.c
> @@ -66,6 +66,19 @@ int sysctl_memory_failure_recovery __read_mostly = 1;
>   
>   atomic_long_t num_poisoned_pages __read_mostly = ATOMIC_LONG_INIT(0);
>   
> +static bool __page_handle_poison(struct page *page)
> +{
> +	bool ret;
> +
> +	zone_pcp_disable(page_zone(page));
> +	ret = dissolve_free_huge_page(page);
> +	if (!ret)
> +		ret = take_page_off_buddy(page);
> +	zone_pcp_enable(page_zone(page));
> +
> +	return ret;
> +}
> +
>   static bool page_handle_poison(struct page *page, bool hugepage_or_freepage, bool release)
>   {
>   	if (hugepage_or_freepage) {
> @@ -73,7 +86,7 @@ static bool page_handle_poison(struct page *page, bool hugepage_or_freepage, boo
>   		 * Doing this check for free pages is also fine since dissolve_free_huge_page
>   		 * returns 0 for non-hugetlb pages as well.
>   		 */
> -		if (dissolve_free_huge_page(page) || !take_page_off_buddy(page))
> +		if (!__page_handle_poison(page))
>   			/*
>   			 * We could fail to take off the target page from buddy
>   			 * for example due to racy page allocation, but that's
> @@ -986,7 +999,7 @@ static int me_huge_page(struct page *p, unsigned long pfn)
>   		 */
>   		if (PageAnon(hpage))
>   			put_page(hpage);
> -		if (!dissolve_free_huge_page(p) && take_page_off_buddy(p)) {
> +		if (__page_handle_poison(p)) {
>   			page_ref_inc(p);
>   			res = MF_RECOVERED;
>   		}
> @@ -1441,7 +1454,7 @@ static int memory_failure_hugetlb(unsigned long pfn, int flags)
>   		res = get_hwpoison_page(p, flags);
>   		if (!res) {
>   			res = MF_FAILED;
> -			if (!dissolve_free_huge_page(p) && take_page_off_buddy(p)) {
> +			if (__page_handle_poison(p)) {
>   				page_ref_inc(p);
>   				res = MF_RECOVERED;
>   			}
> 

Just to make sure: all call paths are fine that we are taking a mutex, 
right?

I can see that get_hwpoison_page() already disables the PCP.

LGTM

-- 
Thanks,

David / dhildenb