Re: [PATCH v19 07/20] mm/vmscan: remove unnecessary lruvec adding

[Alex Shi]

This patch has some conflict on akpm. But since Yu Zhao ask for
revert his patch 'mm: use add_page_to_lru_list()/page_lru()/page_off_lru()'
we should not needs for rebase on it.

Thanks
Alex

在 2020/9/24 上午11:28, Alex Shi 写道:
> We don't have to add a freeable page into lru and then remove from it.
> This change saves a couple of actions and makes the moving more clear.
> 
> The SetPageLRU needs to be kept before put_page_testzero for list
> integrity, otherwise:
> 
>   #0 move_pages_to_lru             #1 release_pages
>   if !put_page_testzero
>      			           if (put_page_testzero())
>      			              !PageLRU //skip lru_lock
>      SetPageLRU()
>      list_add(&page->lru,)
>                                          list_add(&page->lru,)
> 
> [akpm@xxxxxxxxxxxxxxxxxxxx: coding style fixes]
> Signed-off-by: Alex Shi <alex.shi@xxxxxxxxxxxxxxxxx>
> Acked-by: Hugh Dickins <hughd@xxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> Cc: Tejun Heo <tj@xxxxxxxxxx>
> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> Cc: Hugh Dickins <hughd@xxxxxxxxxx>
> Cc: linux-mm@xxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> ---
>  mm/vmscan.c | 38 +++++++++++++++++++++++++-------------
>  1 file changed, 25 insertions(+), 13 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 466fc3144fff..32102e5d354d 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1850,26 +1850,30 @@ static unsigned noinline_for_stack move_pages_to_lru(struct lruvec *lruvec,
>  	while (!list_empty(list)) {
>  		page = lru_to_page(list);
>  		VM_BUG_ON_PAGE(PageLRU(page), page);
> +		list_del(&page->lru);
>  		if (unlikely(!page_evictable(page))) {
> -			list_del(&page->lru);
>  			spin_unlock_irq(&pgdat->lru_lock);
>  			putback_lru_page(page);
>  			spin_lock_irq(&pgdat->lru_lock);
>  			continue;
>  		}
> -		lruvec = mem_cgroup_page_lruvec(page, pgdat);
>  
> +		/*
> +		 * The SetPageLRU needs to be kept here for list integrity.
> +		 * Otherwise:
> +		 *   #0 move_pages_to_lru             #1 release_pages
> +		 *   if !put_page_testzero
> +		 *				      if (put_page_testzero())
> +		 *				        !PageLRU //skip lru_lock
> +		 *     SetPageLRU()
> +		 *     list_add(&page->lru,)
> +		 *                                        list_add(&page->lru,)
> +		 */
>  		SetPageLRU(page);
> -		lru = page_lru(page);
>  
> -		nr_pages = thp_nr_pages(page);
> -		update_lru_size(lruvec, lru, page_zonenum(page), nr_pages);
> -		list_move(&page->lru, &lruvec->lists[lru]);
> -
> -		if (put_page_testzero(page)) {
> +		if (unlikely(put_page_testzero(page))) {
>  			__ClearPageLRU(page);
>  			__ClearPageActive(page);
> -			del_page_from_lru_list(page, lruvec, lru);
>  
>  			if (unlikely(PageCompound(page))) {
>  				spin_unlock_irq(&pgdat->lru_lock);
> @@ -1877,11 +1881,19 @@ static unsigned noinline_for_stack move_pages_to_lru(struct lruvec *lruvec,
>  				spin_lock_irq(&pgdat->lru_lock);
>  			} else
>  				list_add(&page->lru, &pages_to_free);
> -		} else {
> -			nr_moved += nr_pages;
> -			if (PageActive(page))
> -				workingset_age_nonresident(lruvec, nr_pages);
> +
> +			continue;
>  		}
> +
> +		lruvec = mem_cgroup_page_lruvec(page, pgdat);
> +		lru = page_lru(page);
> +		nr_pages = thp_nr_pages(page);
> +
> +		update_lru_size(lruvec, lru, page_zonenum(page), nr_pages);
> +		list_add(&page->lru, &lruvec->lists[lru]);
> +		nr_moved += nr_pages;
> +		if (PageActive(page))
> +			workingset_age_nonresident(lruvec, nr_pages);
>  	}
>  
>  	/*
>