linux-kernel - Re: [PATCH] mm: Remove NULL check in clear_hwpoisoned

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Message-ID: <20190829072712.GS28313@dhcp22.suse.cz>
Date:   Thu, 29 Aug 2019 09:27:12 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Alastair D'Silva <alastair@...ilva.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Wei Yang <richard.weiyang@...il.com>, Qian Cai <cai@....pw>,
        Alexander Duyck <alexander.h.duyck@...ux.intel.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        Baoquan He <bhe@...hat.com>,
        Balbir Singh <bsingharora@...il.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: Remove NULL check in clear_hwpoisoned_pages()

On Thu 29-08-19 13:51:50, Alastair D'Silva wrote:
> There is no possibility for memmap to be NULL in the current
> codebase.
> 
> This check was added in commit 95a4774d055c ("memory-hotplug:
> update mce_bad_pages when removing the memory")
> where memmap was originally inited to NULL, and only conditionally
> given a value.
> 
> The code that could have passed a NULL has been removed, so there

removed by  ba72b4c8cf60 ("mm/sparsemem: support sub-section hotplug")
> is no longer a possibility that memmap can be NULL.

I haven't studied whether section_mem_map could have been NULL before
then but the important part is that NULL is not possible anymore as
pfn_to_page shouldn't ever return NULL.
 
> Signed-off-by: Alastair D'Silva <alastair@...ilva.org>

Acked-by: Michal Hocko <mhocko@...e.com>

Thanks!

> ---
>  mm/sparse.c | 3 ---
>  1 file changed, 3 deletions(-)
> 
> diff --git a/mm/sparse.c b/mm/sparse.c
> index 78979c142b7d..9f7e3682cdcb 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -754,9 +754,6 @@ static void clear_hwpoisoned_pages(struct page *memmap, int nr_pages)
>  {
>  	int i;
>  
> -	if (!memmap)
> -		return;
> -
>  	/*
>  	 * A further optimization is to have per section refcounted
>  	 * num_poisoned_pages.  But that would need more space per memmap, so
> -- 
> 2.21.0

-- 
Michal Hocko
SUSE Labs