Re: [PATCH v3 7/7] mm, page_alloc: disable pcplists during memory offline

[David Hildenbrand]

On 12.11.20 16:18, Vlastimil Babka wrote:
> On 11/11/20 6:58 PM, David Hildenbrand wrote:
> > On 11.11.20 10:28, Vlastimil Babka wrote:
> > > -		/*
> > > -		 * per-cpu pages are drained after start_isolate_page_range, but
> > > -		 * if there are still pages that are not free, make sure that we
> > > -		 * drain again, because when we isolated range we might have
> > > -		 * raced with another thread that was adding pages to pcp list.
> > > -		 *
> > > -		 * Forward progress should be still guaranteed because
> > > -		 * pages on the pcp list can only belong to MOVABLE_ZONE
> > > -		 * because has_unmovable_pages explicitly checks for
> > > -		 * PageBuddy on freed pages on other zones.
> > > -		 */
> > >    		ret = test_pages_isolated(start_pfn, end_pfn, MEMORY_OFFLINE);
> > > -		if (ret)
> > > -			drain_all_pages(zone);
> > > +
> >
> > Why two empty lines before the "} while (ret);" ? (unless I'm confused
> > while looking at this diff)
>
> No there's just a single emply line after "ret = test_pages_isolated..."
> Before there was none, which looked ok with the extra identation of the
> now-removed "drain_all_pages(zone);"
>
> > > +void __zone_set_pageset_high_and_batch(struct zone *zone, unsigned long high,
> > > +		unsigned long batch)
> > > +{
> > > +	struct per_cpu_pageset *p;
> > > +	int cpu;
> > > +
> > > +	for_each_possible_cpu(cpu) {
> > > +		p = per_cpu_ptr(zone->pageset, cpu);
> > > +		pageset_update(&p->pcp, high, batch);
> > > +	}
> > > +}
> > > +
> > >    /*
> > >     * Calculate and set new high and batch values for all per-cpu pagesets of a
> > >     * zone, based on the zone's size and the percpu_pagelist_fraction sysctl.
> > > @@ -6315,8 +6338,6 @@ static void pageset_init(struct per_cpu_pageset *p)
> > >    static void zone_set_pageset_high_and_batch(struct zone *zone)
> > >    {
> > >    	unsigned long new_high, new_batch;
> > > -	struct per_cpu_pageset *p;
> > > -	int cpu;
> > >    
> > >    	if (percpu_pagelist_fraction) {
> > >    		new_high = zone_managed_pages(zone) / percpu_pagelist_fraction;
> > > @@ -6336,10 +6357,7 @@ static void zone_set_pageset_high_and_batch(struct zone *zone)
> > >    	zone->pageset_high = new_high;
> > >    	zone->pageset_batch = new_batch;
> > >    
> > > -	for_each_possible_cpu(cpu) {
> > > -		p = per_cpu_ptr(zone->pageset, cpu);
> > > -		pageset_update(&p->pcp, new_high, new_batch);
> > > -	}
> > > +	__zone_set_pageset_high_and_batch(zone, new_high, new_batch);
> > >    }
> >
> > These two hunks look like an unrelated cleanup, or am I missing something?
>
> It's extracting part of functionality to __zone_set_pageset_high_and_batch()
> that's now called also from zone_pcp_enable() and zone_pcp_disable() - to only
> adjust the per-cpu zone->pageset values without the usual calculation.
>
> > Thanks for looking into this!
>
> Thanks for review. Here's updated version that adds more detailed comment about
> force_all_cpus parameter to __drain_all_pages() header, hopefully that clarifies
> your concerns.


LGTM!

Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>


--
Thanks,

David / dhildenb