linux-kernel - Re: [PATCH v3 3/7] mm/sparse.c: introduce a new function clear_subsection

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Date:   Mon, 9 Mar 2020 14:38:25 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Baoquan He <bhe@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        akpm@...ux-foundation.org, mhocko@...e.com,
        richardw.yang@...ux.intel.com, dan.j.williams@...el.com,
        osalvador@...e.de, rppt@...ux.ibm.com
Subject: Re: [PATCH v3 3/7] mm/sparse.c: introduce a new function
 clear_subsection_map()

On 09.03.20 14:32, Baoquan He wrote:
> On 03/09/20 at 09:59am, David Hildenbrand wrote:
>> On 07.03.20 09:42, Baoquan He wrote:
>>> Factor out the code which clear subsection map of one memory region from
>>> section_deactivate() into clear_subsection_map().
>>>
>>> Signed-off-by: Baoquan He <bhe@...hat.com>
>>> ---
>>>  mm/sparse.c | 31 ++++++++++++++++++++++++-------
>>>  1 file changed, 24 insertions(+), 7 deletions(-)
>>>
>>> diff --git a/mm/sparse.c b/mm/sparse.c
>>> index e37c0abcdc89..d9dcd58d5c1d 100644
>>> --- a/mm/sparse.c
>>> +++ b/mm/sparse.c
>>> @@ -726,15 +726,11 @@ static void free_map_bootmem(struct page *memmap)
>>>  }
>>>  #endif /* CONFIG_SPARSEMEM_VMEMMAP */
>>>  
>>> -static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
>>> -		struct vmem_altmap *altmap)
>>> +static int clear_subsection_map(unsigned long pfn, unsigned long nr_pages)
>>>  {
>>>  	DECLARE_BITMAP(map, SUBSECTIONS_PER_SECTION) = { 0 };
>>>  	DECLARE_BITMAP(tmp, SUBSECTIONS_PER_SECTION) = { 0 };
>>>  	struct mem_section *ms = __pfn_to_section(pfn);
>>> -	bool section_is_early = early_section(ms);
>>> -	struct page *memmap = NULL;
>>> -	bool empty = false;
>>>  	unsigned long *subsection_map = ms->usage
>>>  		? &ms->usage->subsection_map[0] : NULL;
>>>  
>>> @@ -745,8 +741,31 @@ static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
>>>  	if (WARN(!subsection_map || !bitmap_equal(tmp, map, SUBSECTIONS_PER_SECTION),
>>>  				"section already deactivated (%#lx + %ld)\n",
>>>  				pfn, nr_pages))
>>> +		return -EINVAL;
>>> +
>>> +	bitmap_xor(subsection_map, map, subsection_map, SUBSECTIONS_PER_SECTION);
>>> +
>>
>> Nit: I'd drop this line.
> 
> It's fine to me. I usually keep one line for the returning. I will
> remove it when update.
> 
>>
>>> +	return 0;
>>> +}
>>> +
>>> +static bool is_subsection_map_empty(struct mem_section *ms)
>>> +{
>>> +	return bitmap_empty(&ms->usage->subsection_map[0],
>>> +			    SUBSECTIONS_PER_SECTION);
>>> +}
>>> +
>>> +static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
>>> +		struct vmem_altmap *altmap)
>>> +{
>>> +	struct mem_section *ms = __pfn_to_section(pfn);
>>> +	bool section_is_early = early_section(ms);
>>> +	struct page *memmap = NULL;
>>> +	bool empty = false;
>>
>> Nit: No need to initialize empty.
> 
> This is inherited from patch 1.
> 
>>
>>> +
>>> +	if (clear_subsection_map(pfn, nr_pages))
>>>  		return;
>>>  
>>
>> Nit: I'd drop this empty line.
>>
>>> +	empty = is_subsection_map_empty(ms);
>>>  	/*
>>>  	 * There are 3 cases to handle across two configurations
>>>  	 * (SPARSEMEM_VMEMMAP={y,n}):
>>> @@ -764,8 +783,6 @@ static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
>>>  	 *
>>>  	 * For 2/ and 3/ the SPARSEMEM_VMEMMAP={y,n} cases are unified
>>>  	 */
>>> -	bitmap_xor(subsection_map, map, subsection_map, SUBSECTIONS_PER_SECTION);
>>> -	empty = bitmap_empty(subsection_map, SUBSECTIONS_PER_SECTION);
>>
>> I do wonder why you moved this up the comment?
> 
> Since this empty will cover two places of handling, so moved it up,
> seems this is what I was thinking. Can move it back here.

You're moving the whole comment later, was just wondering (makes it
slightly harder to review).


-- 
Thanks,

David / dhildenb