Messages in this thread | | | Date | Tue, 12 Dec 2023 10:32:39 -0800 | From | "Stefan Roesch" <> | Subject | Re: [PATCH v3 1/4] mm/ksm: add ksm advisor |
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On Tue, Dec 12, 2023, at 5:44 AM, David Hildenbrand wrote: > [...] > >> + >> +/** >> + * 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. >
It is needed for patch 2, I folded it into set_advisor_defaults
> 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? >
I think you already saw it, it is used in patch 2, moving the function to patch 2.
>> + >> +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. >
The next version has this change.
>> + >> +/* >> + * 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/
Fixed.
> > Do you also want to describe how min/max CPU comes into play? >
I added additional documentation for it in the next version of the patch.
>> + * 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
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