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

[Matthew Wilcox <willy@infradead.org>]

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.