Re: [PATCH v10 2/5] mm: page_isolation: check specified range for unmovable pages

[David Hildenbrand]

On 12.04.22 16:07, Zi Yan wrote:
> On 12 Apr 2022, at 9:10, David Hildenbrand wrote:
> 
>> On 06.04.22 17:18, Zi Yan wrote:
>>> From: Zi Yan <ziy@xxxxxxxxxx>
>>>
>>> Enable set_migratetype_isolate() to check specified sub-range for
>>> unmovable pages during isolation. Page isolation is done
>>> at MAX_ORDER_NR_PAEGS granularity, but not all pages within that
>>> granularity are intended to be isolated. For example,
>>> alloc_contig_range(), which uses page isolation, allows ranges without
>>> alignment. This commit makes unmovable page check only look for
>>> interesting pages, so that page isolation can succeed for any
>>> non-overlapping ranges.
>>>
>>> Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
>>> ---
>>
>> [...]
>>
>>>  /*
>>> - * This function checks whether pageblock includes unmovable pages or not.
>>> + * This function checks whether the range [start_pfn, end_pfn) includes
>>> + * unmovable pages or not. The range must fall into a single pageblock and
>>> + * consequently belong to a single zone.
>>>   *
>>>   * PageLRU check without isolation or lru_lock could race so that
>>>   * MIGRATE_MOVABLE block might include unmovable pages. And __PageMovable
>>> @@ -28,12 +30,14 @@
>>>   * cannot get removed (e.g., via memory unplug) concurrently.
>>>   *
>>>   */
>>> -static struct page *has_unmovable_pages(struct zone *zone, struct page *page,
>>> -				 int migratetype, int flags)
>>> +static struct page *has_unmovable_pages(unsigned long start_pfn, unsigned long end_pfn,
>>> +				int migratetype, int flags)
>>>  {
>>> -	unsigned long iter = 0;
>>> -	unsigned long pfn = page_to_pfn(page);
>>> -	unsigned long offset = pfn % pageblock_nr_pages;
>>> +	unsigned long pfn = start_pfn;
>>> +	struct page *page = pfn_to_page(pfn);
>>
>>
>> Just do
>>
>> struct page *page = pfn_to_page(start_pfn);
>> struct zone *zone = page_zone(page);
>>
>> here. No need to lookup the zone again in the loop because, as you
>> document "must ... belong to a single zone.".
>>
>> Then, there is also no need to initialize "pfn" here. In the loop header
>> is sufficient.
>>
> 
> Sure.
> 
>>> +
>>> +	VM_BUG_ON(ALIGN_DOWN(start_pfn, pageblock_nr_pages) !=
>>> +		  ALIGN_DOWN(end_pfn - 1, pageblock_nr_pages));
>>>
>>>  	if (is_migrate_cma_page(page)) {
>>>  		/*
>>> @@ -47,8 +51,11 @@ static struct page *has_unmovable_pages(struct zone *zone, struct page *page,
>>>  		return page;
>>>  	}
>>>
>>> -	for (; iter < pageblock_nr_pages - offset; iter++) {
>>> -		page = pfn_to_page(pfn + iter);
>>> +	for (pfn = start_pfn; pfn < end_pfn; pfn++) {
>>> +		struct zone *zone;
>>> +
>>> +		page = pfn_to_page(pfn);
>>> +		zone = page_zone(page);
>>>
>>>  		/*
>>>  		 * Both, bootmem allocations and memory holes are marked
>>> @@ -85,7 +92,7 @@ static struct page *has_unmovable_pages(struct zone *zone, struct page *page,
>>>  			}
>>>
>>>  			skip_pages = compound_nr(head) - (page - head);
>>> -			iter += skip_pages - 1;
>>> +			pfn += skip_pages - 1;
>>>  			continue;
>>>  		}
>>>
>>> @@ -97,7 +104,7 @@ static struct page *has_unmovable_pages(struct zone *zone, struct page *page,
>>>  		 */
>>>  		if (!page_ref_count(page)) {
>>>  			if (PageBuddy(page))
>>> -				iter += (1 << buddy_order(page)) - 1;
>>> +				pfn += (1 << buddy_order(page)) - 1;
>>>  			continue;
>>>  		}
>>>
>>> @@ -134,11 +141,18 @@ static struct page *has_unmovable_pages(struct zone *zone, struct page *page,
>>>  	return NULL;
>>>  }
>>>
>>> -static int set_migratetype_isolate(struct page *page, int migratetype, int isol_flags)
>>> +/*
>>> + * This function set pageblock migratetype to isolate if no unmovable page is
>>> + * present in [start_pfn, end_pfn). The pageblock must intersect with
>>> + * [start_pfn, end_pfn).
>>> + */
>>> +static int set_migratetype_isolate(struct page *page, int migratetype, int isol_flags,
>>> +			unsigned long start_pfn, unsigned long end_pfn)
>>
>> I think we might be able do better, eventually not passing start_pfn at
>> all. Hmm.
> 
> IMHO, having start_pfn and end_pfn in the parameter list would make the
> interface easier to understand. Otherwise if we remove start_pfn,
> the caller needs to adjust @page to be within the range of [start_pfn,
> end_pfn)
> 
>>
>> I think we want to pull out the
>> start_isolate_page_range()/undo_isolate_page_range() interface change
>> into a separate patch.
> 
> You mean a patch just adding
> 
> unsigned long isolate_start = pfn_max_align_down(start_pfn);
> unsigned long isolate_end = pfn_max_align_up(end_pfn);
> 
> in start_isolate_page_range()/undo_isolate_page_range()?
> 
> Yes I can do that.

I think we have to be careful with memory onlining/offlining. There are
corner cases where we get called with only pageblock alignment and
must not adjust the range.


Something like this as a base for the next cleanups/extensions: