linux-kernel - Re: [PATCH] mm,memory_hotplug: Fix scan_movable

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Date:   Tue, 29 Jan 2019 11:03:56 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Oscar Salvador <osalvador@...e.de>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, mhocko@...e.com
Subject: Re: [PATCH] mm,memory_hotplug: Fix scan_movable_pages for gigantic
 hugepages

On 28.01.19 23:56, Andrew Morton wrote:
> On Mon, 28 Jan 2019 14:53:09 -0800 Andrew Morton <akpm@...ux-foundation.org> wrote:
> 
>> On Fri, 25 Jan 2019 08:58:33 +0100 Oscar Salvador <osalvador@...e.de> wrote:
>>
>>> On Wed, Jan 23, 2019 at 11:33:56AM +0100, David Hildenbrand wrote:
>>>> If you use {} for the else case, please also do so for the if case.
>>>
>>> Diff on top:
>>>
>>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>>> index 25aee4f04a72..d5810e522b72 100644
>>> --- a/mm/memory_hotplug.c
>>> +++ b/mm/memory_hotplug.c
>>> @@ -1338,9 +1338,9 @@ static unsigned long scan_movable_pages(unsigned long start, unsigned long end)
>>>  				struct page *head = compound_head(page);
>>>  
>>>  				if (hugepage_migration_supported(page_hstate(head)) &&
>>> -				    page_huge_active(head))
>>> +				    page_huge_active(head)) {
>>>  					return pfn;
>>> -				else {
>>> +				} else {
>>>  					unsigned long skip;
>>>  
>>>  					skip = (1 << compound_order(head)) - (page - head);
>>>
>>
>> The indenting is getting a bit deep also, so how about this?
>>
>> static unsigned long scan_movable_pages(unsigned long start, unsigned long end)
>> {
>> 	unsigned long pfn;
>>
>> 	for (pfn = start; pfn < end; pfn++) {
>> 		struct page *page, *head;
>> 	
>> 		if (!pfn_valid(pfn))
>> 			continue;
>> 		page = pfn_to_page(pfn);
>> 		if (PageLRU(page))
>> 			return pfn;
>> 		if (__PageMovable(page))
>> 			return pfn;
>>
>> 		if (!PageHuge(page))
>> 			continue;
>> 		head = compound_head(page);
>> 		if (hugepage_migration_supported(page_hstate(head)) &&
>> 		    page_huge_active(head)) {
>> 			return pfn;
> 
> checkpatch pointed out that else-after-return isn't needed so we can do
> 
> static unsigned long scan_movable_pages(unsigned long start, unsigned long end)
> {
> 	unsigned long pfn;
> 
> 	for (pfn = start; pfn < end; pfn++) {
> 		struct page *page, *head;
> 		unsigned long skip;
> 
> 		if (!pfn_valid(pfn))
> 			continue;
> 		page = pfn_to_page(pfn);
> 		if (PageLRU(page))
> 			return pfn;
> 		if (__PageMovable(page))
> 			return pfn;
> 
> 		if (!PageHuge(page))
> 			continue;
> 		head = compound_head(page);
> 		if (hugepage_migration_supported(page_hstate(head)) &&
> 		    page_huge_active(head))
> 			return pfn;
> 		skip = (1 << compound_order(head)) - (page - head);
> 		pfn += skip - 1;
> 	}
> 	return 0;
> }
> 
> --- a/mm/memory_hotplug.c~mmmemory_hotplug-fix-scan_movable_pages-for-gigantic-hugepages-fix
> +++ a/mm/memory_hotplug.c
> @@ -1305,28 +1305,27 @@ int test_pages_in_a_zone(unsigned long s
>  static unsigned long scan_movable_pages(unsigned long start, unsigned long end)
>  {
>  	unsigned long pfn;
> -	struct page *page;
> +
>  	for (pfn = start; pfn < end; pfn++) {
> -		if (pfn_valid(pfn)) {
> -			page = pfn_to_page(pfn);
> -			if (PageLRU(page))
> -				return pfn;
> -			if (__PageMovable(page))
> -				return pfn;
> -			if (PageHuge(page)) {
> -				struct page *head = compound_head(page);
> +		struct page *page, *head;
> +		unsigned long skip;
>  
> -				if (hugepage_migration_supported(page_hstate(head)) &&
> -				    page_huge_active(head))
> -					return pfn;
> -				else {
> -					unsigned long skip;
> +		if (!pfn_valid(pfn))
> +			continue;
> +		page = pfn_to_page(pfn);
> +		if (PageLRU(page))
> +			return pfn;
> +		if (__PageMovable(page))
> +			return pfn;
>  
> -					skip = (1 << compound_order(head)) - (page - head);
> -					pfn += skip - 1;
> -				}
> -			}
> -		}
> +		if (!PageHuge(page))
> +			continue;
> +		head = compound_head(page);
> +		if (hugepage_migration_supported(page_hstate(head)) &&
> +		    page_huge_active(head))
> +			return pfn;
> +		skip = (1 << compound_order(head)) - (page - head);
> +		pfn += skip - 1;

Not sure if encoding the -1 in the previous line is even better now that
we have more space

skip = (1 << compound_order(head)) - (page - head + 1);

Looks good to me.

>  	}
>  	return 0;
>  }
> _
> 


-- 

Thanks,

David / dhildenb