linux-kernel - Re: [PATCH 2/3] mm/page_ext: remove rollback for untouched mem_section in online_page

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Message-ID: <af36016f-6143-ad66-385e-bb64a6205863@huaweicloud.com>
Date:   Mon, 17 Jul 2023 09:47:08 +0800
From:   Kemeng Shi <shikemeng@...weicloud.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] mm/page_ext: remove rollback for untouched
 mem_section in online_page_ext



on 7/15/2023 1:54 AM, Andrew Morton wrote:
> On Fri, 14 Jul 2023 19:47:48 +0800 Kemeng Shi <shikemeng@...weicloud.com> wrote:
> 
>> If init_section_page_ext failed, we only need rollback for mem_section
>> before failed mem_section. Make rollback end point to failed mem_section
>> to remove unnecessary rollback.
>>
>> As pfn += PAGES_PER_SECTION will be executed even if init_section_page_ext
>> failed. So pfn points to mem_section after failed mem_section. Subtract
>> one mem_section from pfn to get failed mem_section.
>>
>> ...
>>
>> --- a/mm/page_ext.c
>> +++ b/mm/page_ext.c
>> @@ -424,6 +424,7 @@ static int __meminit online_page_ext(unsigned long start_pfn,
>>  		return 0;
>>  
>>  	/* rollback */
>> +	end = pfn - PAGES_PER_SECTION;
>>  	for (pfn = start; pfn < end; pfn += PAGES_PER_SECTION)
>>  		__free_page_ext(pfn);
>>  
> 
> This is a bugfix, yes?
> 
> I guess init_section_page_ext() never fails for anyone...
I marked this as cleanup because __free_page_ext can handle NULL page_ext
from uninitialized mem_section. Then no real bug will be triggered even
if init_section_page_ext failed.
-- 
Best wishes
Kemeng Shi