Re: [PATCH] mm/vmpressure: scale window size based on machine memory and CPU count

Andrew Morton
2026-02-27T20:28:58Z

On Fri, 27 Feb 2026 10:33:33 -0600 Benjamin Lee McQueen <mcq@disroot.org> wrote:

> the vmpressure window size was recently fixed at 512 pages regardless
> of machine size, this patch makes it scale based on the machine memory
> and CPU count.

Why? Presumably the current code is causing some problem - please
fully describe that.

> --- a/mm/vmpressure.c
> +++ b/mm/vmpressure.c
> @@ -32,10 +32,20 @@
> * As the vmscan reclaimer logic works with chunks which are multiple of
> * SWAP_CLUSTER_MAX, it makes sense to use it for the window size as well.
> *
> - * TODO: Make the window size depend on machine size, as we do for vmstat
> - * thresholds. Currently we set it to 512 pages (2MB for 4KB pages).
> + * Window size is now scaled based on RAM and CPU size, similarly to how
> + * vmstat checks them.
> */
> -static const unsigned long vmpressure_win = SWAP_CLUSTER_MAX * 16;
> +static unsigned long vmpressure_win;
> +
> +static int __init vmpressure_win_init(void)
> +{
> + unsigned long mem = totalram_pages() >> (27 - PAGE_SHIFT);
> +
> + vmpressure_win = SWAP_CLUSTER_MAX * max(16UL,
> + 2UL * fls(num_online_cpus()) * (1 + fls(mem)));
> + return 0;
> +}
> +core_initcall(vmpressure_win_init);

Whitespace is odd.