Messages in this thread | | | Date | Tue, 12 Dec 2023 14:44:04 +0100 | Subject | Re: [PATCH v3 1/4] mm/ksm: add ksm advisor | From | David Hildenbrand <> |
| |
[...]
> + > +/** > + * struct advisor_ctx - metadata for KSM advisor > + * @start_scan: start time of the current scan > + * @scan_time: scan time of previous scan > + * @change: change in percent to pages_to_scan parameter > + * @cpu_time: cpu time consumed by the ksmd thread in the previous scan > + */ > +struct advisor_ctx { > + ktime_t start_scan; > + unsigned long scan_time; > + unsigned long change; > + unsigned long long cpu_time; > +}; > +static struct advisor_ctx advisor_ctx; > + > +/* Define different advisor's */ > +enum ksm_advisor_type { > + KSM_ADVISOR_NONE, > + KSM_ADVISOR_SCAN_TIME, > +}; > +static enum ksm_advisor_type ksm_advisor; > + > +static void init_advisor(void) > +{ > + advisor_ctx = (const struct advisor_ctx){ 0 }; > +}
Again, you can drop this completely. The static values are already initialized to 0.
Or is there any reason to initialize to 0 explicitly?
> + > +static void set_advisor_defaults(void) > +{ > + if (ksm_advisor == KSM_ADVISOR_NONE) > + ksm_thread_pages_to_scan = DEFAULT_PAGES_TO_SCAN; > + else if (ksm_advisor == KSM_ADVISOR_SCAN_TIME) > + ksm_thread_pages_to_scan = ksm_advisor_min_pages; > +}
That function is unused?
> + > +static inline void advisor_start_scan(void) > +{ > + if (ksm_advisor == KSM_ADVISOR_SCAN_TIME) > + advisor_ctx.start_scan = ktime_get(); > +} > + > +static inline s64 advisor_stop_scan(void) > +{ > + return ktime_ms_delta(ktime_get(), advisor_ctx.start_scan); > +}
Just inline that into the caller. Then rename run_advisor() into advisor_stop_scan(). So in scan_get_next_rmap_item)( you have paired start+stop hooks.
> + > +/* > + * Use previous scan time if available, otherwise use current scan time as an > + * approximation for the previous scan time. > + */ > +static inline unsigned long prev_scan_time(struct advisor_ctx *ctx, > + unsigned long scan_time) > +{ > + return ctx->scan_time ? ctx->scan_time : scan_time; > +} > + > +/* Calculate exponential weighted moving average */ > +static unsigned long ewma(unsigned long prev, unsigned long curr) > +{ > + return ((100 - EWMA_WEIGHT) * prev + EWMA_WEIGHT * curr) / 100; > +} > + > +/* > + * The scan time advisor is based on the current scan rate and the target > + * scan rate. > + * > + * new_pages_to_scan = pages_to_scan * (scan_time / target_scan_time) > + * > + * To avoid pertubations it calculates a change factor of previous changes.
s/pertubations/perturbations/
Do you also want to describe how min/max CPU comes into play?
> + * A new change factor is calculated for each iteration and it uses an > + * exponentially weighted moving average. The new pages_to_scan value is > + * multiplied with that change factor: > + * > + * new_pages_to_scan *= change facor > + * > + * In addition the new pages_to_scan value is capped by the max and min > + * limits. > + */
With that, LGTM
Acked-by: David Hildenbrand <david@redhat.com>
-- Cheers,
David / dhildenb
| |