Re: [PATCH 03/10] Use percpu stats

Andrew Morton
2010-08-10T04:33:08Z

On Mon, 9 Aug 2010 22:56:49 +0530 Nitin Gupta <ngupta@vflare.org> wrote:

> +/*
> + * Individual percpu values can go negative but the sum across all CPUs
> + * must always be positive (we store various counts). So, return sum as
> + * unsigned value.
> + */
> +static u64 zram_get_stat(struct zram *zram, enum zram_stats_index idx)
> {
> - u64 val;
> -
> - spin_lock(&zram->stat64_lock);
> - val = *v;
> - spin_unlock(&zram->stat64_lock);
> + int cpu;
> + s64 val = 0;
> +
> + for_each_possible_cpu(cpu) {
> + s64 temp;
> + unsigned int start;
> + struct zram_stats_cpu *stats;
> +
> + stats = per_cpu_ptr(zram->stats, cpu);
> + do {
> + start = u64_stats_fetch_begin(&stats->syncp);
> + temp = stats->count[idx];
> + } while (u64_stats_fetch_retry(&stats->syncp, start));
> + val += temp;
> + }
>
> + WARN_ON(val < 0);
> return val;
> }

That reimplements include/linux/percpu_counter.h, poorly.

Please see the June discussion "[PATCH v2 1/2] tmpfs: Quick token
library to allow scalable retrieval of tokens from token jar" for some
discussion.