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SubjectRe: [RFC 4/5] mm, page_alloc: cache pageset high and batch in struct zone
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On 9/10/20 1:30 PM, Oscar Salvador wrote:
> On Mon, Sep 07, 2020 at 06:36:27PM +0200, Vlastimil Babka wrote:
> */
>> -static void setup_pageset(struct per_cpu_pageset *p);
>> +static void pageset_init(struct per_cpu_pageset *p);
>
> this belongs to the respective patches

Right, thanks.

>> -static void zone_set_pageset_high_and_batch(struct zone *zone)
>> +static void zone_set_pageset_high_and_batch(struct zone *zone, bool force_update)
>> {
>> unsigned long new_high;
>> unsigned long new_batch;
>> @@ -6256,6 +6256,14 @@ static void zone_set_pageset_high_and_batch(struct zone *zone)
>> new_batch = max(1UL, 1 * new_batch);
>> }
>>
>> + if (zone->pageset_high != new_high ||
>> + zone->pageset_batch != new_batch) {
>> + zone->pageset_high = new_high;
>> + zone->pageset_batch = new_batch;
>> + } else if (!force_update) {
>> + return;
>> + }
>
> I am probably missimg something obvious, so sorry, but why do we need
> force_update here?
> AFAICS, we only want to call pageset_update() in case zone->pageset_high/batch
> and the new computed high/batch differs, so if everything is equal, why do we want
> to call it anyways?

My reasoning is that initially we don't have guarantee that
zone->pageset_high/batch matches the respective pcp->high/batch. So we could
detect no change in the zone values and return, but leave the pcp value
incoherent. But now I think it could be achieved also in a simpler way, so I'll try.


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