linux-kernel - Re: [PATCH] mm: vmscan: support equal reclaim for anon and file pages

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Message-ID: <20210112070310.GE22493@dhcp22.suse.cz>
Date:   Tue, 12 Jan 2021 08:03:10 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Sudarshan Rajagopalan <sudaraja@...eaurora.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        akpm@...ux-foundation.org
Subject: Re: [PATCH] mm: vmscan: support equal reclaim for anon and file pages

On Mon 11-01-21 12:58:43, Sudarshan Rajagopalan wrote:
> When performing memory reclaim support treating anonymous and
> file backed pages equally.
> Swapping anonymous pages out to memory can be efficient enough
> to justify treating anonymous and file backed pages equally.

This changelog doesn't explain, what kind of problem you are trying to
address, why the existing code and tunables are insufficient, how it is
supposed to work, what are potential risks, what kind of testing have
you done and more.

Please have a look at Documentation/process/submitting-patches.rst for
more guidance about expectations from a patch when it is submitted.
 
> Signed-off-by: Sudarshan Rajagopalan <sudaraja@...eaurora.org>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> ---
>  mm/vmscan.c | 15 +++++++++++++--
>  1 file changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 257cba79a96d..ec7585e0d5f5 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -169,6 +169,8 @@ struct scan_control {
>   */
>  int vm_swappiness = 60;
>  
> +bool balance_anon_file_reclaim = false;
> +
>  static void set_task_reclaim_state(struct task_struct *task,
>  				   struct reclaim_state *rs)
>  {
> @@ -201,6 +203,13 @@ static DECLARE_RWSEM(shrinker_rwsem);
>  static DEFINE_IDR(shrinker_idr);
>  static int shrinker_nr_max;
>  
> +static int __init cmdline_parse_balance_reclaim(char *p)
> +{
> +	balance_anon_file_reclaim = true;
> +	return 0;
> +}
> +early_param("balance_reclaim", cmdline_parse_balance_reclaim);
> +
>  static int prealloc_memcg_shrinker(struct shrinker *shrinker)
>  {
>  	int id, ret = -ENOMEM;
> @@ -2291,9 +2300,11 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
>  
>  	/*
>  	 * If there is enough inactive page cache, we do not reclaim
> -	 * anything from the anonymous working right now.
> +	 * anything from the anonymous working right now. But when balancing
> +	 * anon and page cache files for reclaim, allow swapping of anon pages
> +	 * even if there are a number of inactive file cache pages.
>  	 */
> -	if (sc->cache_trim_mode) {
> +	if (!balance_anon_file_reclaim && sc->cache_trim_mode) {
>  		scan_balance = SCAN_FILE;
>  		goto out;
>  	}
> -- 
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
> a Linux Foundation Collaborative Project
> 

-- 
Michal Hocko
SUSE Labs