Re: [PATCH 3/4] Per cgroup background reclaim.

[KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>]

> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index a15bc1c..dc61f2a 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -615,6 +615,7 @@ static void free_pcppages_bulk(struct zone *zone, int count,
>  
>  		do {
>  			page = list_entry(list->prev, struct page, lru);
> +			mem_cgroup_clear_unreclaimable(page, zone);
>  			/* must delete as __free_one_page list manipulates */
>  			list_del(&page->lru);
>  			/* MIGRATE_MOVABLE list may include MIGRATE_RESERVEs */
> @@ -632,6 +633,7 @@ static void free_one_page(struct zone *zone, struct page *page, int order,
>  	spin_lock(&zone->lock);
>  	zone->all_unreclaimable = 0;
>  	zone->pages_scanned = 0;
> +	mem_cgroup_clear_unreclaimable(page, zone);
>  
>  	__free_one_page(page, zone, order, migratetype);
>  	__mod_zone_page_state(zone, NR_FREE_PAGES, 1 << order);

Please don't do that. free page is one of fast path. We don't want to add
additonal overhead here.

So I would like to explain why we clear zone->all_unreclaimable in free 
page path at first. Look, zone free pages are maintained by NR_FREE_PAGES
and free_one_page modify it.

But, free_one_page() is unrelated to memory cgroup uncharge thing. If nobody
does memcg uncharge, reclaim retrying is pointless. no? I think we have
better place than here.



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