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

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Date:   Thu, 12 Nov 2020 17:09:07 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Vlastimil Babka <vbabka@...e.cz>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Michal Hocko <mhocko@...nel.org>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Oscar Salvador <osalvador@...e.de>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Michal Hocko <mhocko@...e.com>
Subject: Re: [PATCH v3 7/7] mm, page_alloc: disable pcplists during memory
 offline

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@...hat.com>


-- 
Thanks,

David / dhildenb