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

[Yang Shi]

On Mon, Jan 11, 2021 at 12:59 PM Sudarshan Rajagopalan
<sudaraja@xxxxxxxxxxxxxx> 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.
>
> Signed-off-by: Sudarshan Rajagopalan <sudaraja@xxxxxxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> ---
>  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;

I think the same effect could be achieved by adjusting swappiness. The
"swappiness" can go to 200 now.

Please check the document at Documentation/admin-guide/sysctl/vm.rst, it says:

This control is used to define the rough relative IO cost of swapping
and filesystem paging, as a value between 0 and 200. At 100, the VM
assumes equal IO cost and will thus apply memory pressure to the page
cache and swap-backed pages equally; lower values signify more
expensive swap IO, higher values indicates cheaper.

> +
>  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;
>         }
> --
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>
>