linux-kernel - Re: [PATCH -V8 07/10] mm/vmscan: add helper for querying ability to age anonymous pages

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Date:   Fri, 18 Jun 2021 11:45:50 -0400
From:   Zi Yan <ziy@...dia.com>
To:     Huang Ying <ying.huang@...el.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Yang Shi <shy828301@...il.com>,
        Greg Thelen <gthelen@...gle.com>,
        Michal Hocko <mhocko@...e.com>, Wei Xu <weixugc@...gle.com>,
        David Rientjes <rientjes@...gle.com>,
        Dan Williams <dan.j.williams@...el.com>,
        David Hildenbrand <david@...hat.com>,
        osalvador <osalvador@...e.de>
Subject: Re: [PATCH -V8 07/10] mm/vmscan: add helper for querying ability to age anonymous pages

On 18 Jun 2021, at 2:15, Huang Ying wrote:

> From: Dave Hansen <dave.hansen@...ux.intel.com>
>
> Anonymous pages are kept on their own LRU(s).  These lists could
> theoretically always be scanned and maintained.  But, without swap,
> there is currently nothing the kernel can *do* with the results of a
> scanned, sorted LRU for anonymous pages.
>
> A check for '!total_swap_pages' currently serves as a valid check as
> to whether anonymous LRUs should be maintained.  However, another
> method will be added shortly: page demotion.
>
> Abstract out the 'total_swap_pages' checks into a helper, give it a
> logically significant name, and check for the possibility of page
> demotion.
>
> Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
> Signed-off-by: "Huang, Ying" <ying.huang@...el.com>
> Reviewed-by: Yang Shi <shy828301@...il.com>
> Reviewed-by: Greg Thelen <gthelen@...gle.com>
> Cc: Michal Hocko <mhocko@...e.com>
> Cc: Wei Xu <weixugc@...gle.com>
> Cc: David Rientjes <rientjes@...gle.com>
> Cc: Dan Williams <dan.j.williams@...el.com>
> Cc: David Hildenbrand <david@...hat.com>
> Cc: osalvador <osalvador@...e.de>
> ---
>  mm/vmscan.c | 28 +++++++++++++++++++++++++---
>  1 file changed, 25 insertions(+), 3 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 7d5c7216a4b7..8654cec65522 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2706,6 +2706,26 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
>  	}
>  }
>
> +/*
> + * Anonymous LRU management is a waste if there is
> + * ultimately no way to reclaim the memory.
> + */
> +bool anon_should_be_aged(struct lruvec *lruvec)
> +{
> +	struct pglist_data *pgdat = lruvec_pgdat(lruvec);
> +
> +	/* Aging the anon LRU is valuable if swap is present: */
> +	if (total_swap_pages > 0)
> +		return true;
> +
> +	/* Also valuable if anon pages can be demoted: */
> +	if (next_demotion_node(pgdat->node_id) >= 0)

!= NUMA_NO_NODE might be better, even though we know NUMA_NO_NODE
is currently set to -1.

> +		return true;
> +
> +	/* No way to reclaim anon pages.  Should not age anon LRUs: */
> +	return false;
> +}
> +
>  static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
>  {
>  	unsigned long nr[NR_LRU_LISTS];
> @@ -2815,7 +2835,8 @@ static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
>  	 * Even if we did not try to evict anon pages at all, we want to
>  	 * rebalance the anon lru active/inactive ratio.
>  	 */
> -	if (total_swap_pages && inactive_is_low(lruvec, LRU_INACTIVE_ANON))
> +	if (anon_should_be_aged(lruvec) &&
> +	    inactive_is_low(lruvec, LRU_INACTIVE_ANON))
>  		shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
>  				   sc, LRU_ACTIVE_ANON);
>  }
> @@ -3644,10 +3665,11 @@ static void age_active_anon(struct pglist_data *pgdat,
>  	struct mem_cgroup *memcg;
>  	struct lruvec *lruvec;
>
> -	if (!total_swap_pages)
> +	lruvec = mem_cgroup_lruvec(NULL, pgdat);
> +
> +	if (!anon_should_be_aged(lruvec))
>  		return;
>
> -	lruvec = mem_cgroup_lruvec(NULL, pgdat);
>  	if (!inactive_is_low(lruvec, LRU_INACTIVE_ANON))
>  		return;
>
> -- 
> 2.30.2


—
Best Regards,
Yan, Zi

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