Re: [PATCH 2/2] lru: allow large batched add large folio to lru list

[Yin Fengwei <fengwei.yin@intel.com>]

Add Ying who found out the large folio is not batched added to lru.

On 4/18/23 09:57, Yin Fengwei wrote:
> 
> 
> On 4/17/23 20:25, Matthew Wilcox wrote:
>> On Mon, Apr 17, 2023 at 03:56:43PM +0800, Yin Fengwei wrote:
>>> Currently, large folio is not batched added to lru list. Which
>>> cause high lru lock contention after enable large folio for
>>> anonymous mappping.
>>
>> Obviously, I think we should be doing a batched add, but I don't think
>> this is right.
>>
>>> @@ -54,7 +57,12 @@ static inline unsigned pagevec_space(struct pagevec *pvec)
>>>  static inline unsigned pagevec_add(struct pagevec *pvec, struct page *page)
>>>  {
>>>  	pvec->pages[pvec->nr++] = page;
>>> -	return pagevec_space(pvec);
>>> +	pvec->pages_nr += compound_nr(page);
>>> +
>>> +	if (pvec->pages_nr > PAGEVEC_SIZE)
>>> +		return 0;
>>> +	else
>>> +		return pagevec_space(pvec);
>>
>> I assume your thinking here is that we should limit the number of pages
>> in the batches, but I think we should allow the number of folios to reach
>> PAGEVEC_SIZE before we drain the batch onto the LRU list.  That will
>> reduce the contention on the LRU lock even further.
> 
> Yes. The first thought in my mind was to limit the number of folios also.
> 
> But the concern is that large folio has wider range of size. In the extreme
> case, if all batched large folios has 2M size, with PAGEVEC_SIZE as 15,
> one batch could have 30M memory. Which could be too large for some usages.
> 
> 
> Regards
> Yin, Fengwei
> 
>>