On Thu, May 14, 2020 at 03:04:24PM +0800, Huang Ying wrote:
> And the pmbench score increases 15.9%.
What metric is that, and how long did you run the benchmark for?
Given that this thing is probabilistic, did you notice much variance from run
to run?
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 35be7a7271f4..9f1343b066c1 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -746,7 +746,16 @@ static int scan_swap_map_slots(struct swap_info_struct *si,
> */
>
> si->flags += SWP_SCANNING;
> - scan_base = offset = si->cluster_next;
> + /*
> + * Use percpu scan base for SSD to reduce lock contention on
> + * cluster and swap cache. For HDD, sequential access is more
> + * important.
> + */
> + if (si->flags & SWP_SOLIDSTATE)
> + scan_base = this_cpu_read(*si->cluster_next_cpu);
> + else
> + scan_base = si->cluster_next;
> + offset = scan_base;
>
> /* SSD algorithm */
> if (si->cluster_info) {
It's just a nit but SWP_SOLIDSTATE and 'if (si->cluster_info)' are two ways to
check the same thing and I'd stick with the one that's already there.
> @@ -2962,6 +2979,8 @@ static unsigned long read_swap_header(struct swap_info_struct *p,
>
> p->lowest_bit = 1;
> p->cluster_next = 1;
> + for_each_possible_cpu(i)
> + per_cpu(*p->cluster_next_cpu, i) = 1;
These are later overwritten if the device is an SSD which seems to be the only
case where these are used, so why have this?
> p->cluster_nr = 0;
>
> maxpages = max_swapfile_size();
> @@ -3204,6 +3223,10 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
> * SSD
> */
> p->cluster_next = 1 + prandom_u32_max(p->highest_bit);
> + for_each_possible_cpu(cpu) {
> + per_cpu(*p->cluster_next_cpu, cpu) =
> + 1 + prandom_u32_max(p->highest_bit);
> + }
Is there a reason for adding one? The history didn't enlighten me about why
cluster_next does it.
