linux-kernel - Re: [RFC PATCH v2 01/16] mm,hwpoison: cleanup unused PageHuge() check

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Date:   Fri, 18 Oct 2019 13:48:32 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Oscar Salvador <osalvador@...e.de>
Cc:     n-horiguchi@...jp.nec.com, mike.kravetz@...cle.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v2 01/16] mm,hwpoison: cleanup unused PageHuge() check

On Thu 17-10-19 16:21:08, Oscar Salvador wrote:
> From: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
> 
> Drop the PageHuge check since memory_failure forks into memory_failure_hugetlb()
> for hugetlb pages.
> 
> Signed-off-by: Oscar Salvador <osalvador@...e.de>
> Signed-off-by: Naoya Horiguchi <n-horiguchi@...jp.nec.com>

s-o-b chain is reversed.

The code is a bit confusing. Doesn't this check aim for THP? AFAICS
PageTransHuge(hpage) will split the THP or fail so PageTransHuge
shouldn't be possible anymore, right? But why does hwpoison_user_mappings
still work with hpage then?

> ---
>  mm/memory-failure.c | 5 +----
>  1 file changed, 1 insertion(+), 4 deletions(-)
> 
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 05c8c6df25e6..2cbadb58c7df 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -1345,10 +1345,7 @@ int memory_failure(unsigned long pfn, int flags)
>  	 * page_remove_rmap() in try_to_unmap_one(). So to determine page status
>  	 * correctly, we save a copy of the page flags at this time.
>  	 */
> -	if (PageHuge(p))
> -		page_flags = hpage->flags;
> -	else
> -		page_flags = p->flags;
> +	page_flags = p->flags;
>  
>  	/*
>  	 * unpoison always clear PG_hwpoison inside page lock
> -- 
> 2.12.3

-- 
Michal Hocko
SUSE Labs