On Fri, Apr 05, 2024 at 05:35:07AM +0000, Yosry Ahmed wrote:
> Currently, we calculate the zswap global limit, and potentially the
> acceptance threshold in the zswap, in pages in the zswap store path.
> This is unnecessary because the values rarely change.
>
> Instead, precalculate the them when the module parameters are updated,
> which should be rare. Since we are adding custom handlers for setting
> the percentages now, add proper validation that they are <= 100.
>
> Suggested-by: Johannes Weiner <hannes@xxxxxxxxxxx>
> Signed-off-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
Nice! Getting that stuff out of the hotpath!
Two comments below:
> @@ -684,6 +703,43 @@ static int zswap_enabled_param_set(const char *val,
> return ret;
> }
>
> +static int __zswap_percent_param_set(const char *val,
> + const struct kernel_param *kp)
> +{
> + unsigned int n;
> + int ret;
> +
> + ret = kstrtouint(val, 10, &n);
> + if (ret || n > 100)
> + return -EINVAL;
> +
> + return param_set_uint(val, kp);
> +}
> +
> +static int zswap_max_pool_param_set(const char *val,
> + const struct kernel_param *kp)
> +{
> + int err = __zswap_percent_param_set(val, kp);
> +
> + if (!err) {
> + zswap_update_max_pages();
> + zswap_update_accept_thr_pages();
> + }
> +
> + return err;
> +}
> +
> +static int zswap_accept_thr_param_set(const char *val,
> + const struct kernel_param *kp)
> +{
> + int err = __zswap_percent_param_set(val, kp);
> +
> + if (!err)
> + zswap_update_accept_thr_pages();
> +
> + return err;
> +}
I think you can keep this simple and just always update both if
anything changes for whatever reason. It's an extremely rare event
after all. That should cut it from 3 functions to 1.
Note that totalram_pages can also change during memory onlining and
offlining. For that you need a memory notifier that also calls that
refresh function. It's simple enough, though, check out the code
around register_memory_notifier() in drivers/xen/balloon.c.
