Re: [PATCH 4/4] mm/page_alloc : relieve zone->lock's pressure for memory free

[Huang Shijie <shijie8@gmail.com>]

>>    Move the __mod_zone_page_state out the guard region of
>> the spinlock to relieve the pressure for memory free.
>>
>> Signed-off-by: Huang Shijie<shijie8@gmail.com>
>> ---
>>   mm/page_alloc.c |   26 ++++++++++++++++----------
>>   1 files changed, 16 insertions(+), 10 deletions(-)
>>
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 290dfc3..34b9a3a 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -530,12 +530,9 @@ static void free_pcppages_bulk(struct zone *zone, int count,
>>   {
>>   	int migratetype = 0;
>>   	int batch_free = 0;
>> +	int free_ok = 0;
>>
>>   	spin_lock(&zone->lock);
>> -	zone_clear_flag(zone, ZONE_ALL_UNRECLAIMABLE);
>> -	zone->pages_scanned = 0;
>>      
>
> We don't use zone->lock to protect pages_scanned in shrink_[in]active_list.
> At least, we can move zone->pages_scanned out of lock.
>
> In addition,
> sometime we don't use lock to test ZONE_ALL_UNRECLAIMABLE,
> sometime we do use zone->lock(ex, zoneinfo_show_print).
>
> Now lock for ZONE_ALL_UNRECLAIMABLE is not consistent,
>
> I think we have to use not zone->lock but zone->lru_lock
> since it's related to reclaim.
>
>    
agree.
  I think zone->lru_lock is more proper.

> Few days ago, Mel and Kosaki discussed about zone->lock.
> Any thought?
>
>    
>> -
>> -	__mod_zone_page_state(zone, NR_FREE_PAGES, count);
>>   	while (count) {
>>   		struct page *page;
>>   		struct list_head *list;
>> @@ -558,23 +555,32 @@ static void free_pcppages_bulk(struct zone *zone, int count,
>>   			page = list_entry(list->prev, struct page, lru);
>>   			/* must delete as __free_one_page list manipulates */
>>   			list_del(&page->lru);
>> -			__free_one_page(page, zone, 0, migratetype);
>> +			free_ok += __free_one_page(page, zone, 0, migratetype);
>>   			trace_mm_page_pcpu_drain(page, 0, migratetype);
>>   		} while (--count&&  --batch_free&&  !list_empty(list));
>>   	}
>> +
>> +	if (likely(free_ok)) {
>> +		zone_clear_flag(zone, ZONE_ALL_UNRECLAIMABLE);
>> +		zone->pages_scanned = 0;
>> +	}
>>   	spin_unlock(&zone->lock);
>> +	__mod_zone_page_state(zone, NR_FREE_PAGES, free_ok);
>>   }
>>
>>   static void free_one_page(struct zone *zone, struct page *page, int order,
>>   				int migratetype)
>>   {
>> -	spin_lock(&zone->lock);
>> -	zone_clear_flag(zone, ZONE_ALL_UNRECLAIMABLE);
>> -	zone->pages_scanned = 0;
>> +	int free_ok;
>>
>> -	__mod_zone_page_state(zone, NR_FREE_PAGES, 1<<  order);
>> -	__free_one_page(page, zone, order, migratetype);
>> +	spin_lock(&zone->lock);
>> +	free_ok = __free_one_page(page, zone, order, migratetype);
>> +	if (likely(free_ok)) {
>> +		zone_clear_flag(zone, ZONE_ALL_UNRECLAIMABLE);
>> +		zone->pages_scanned = 0;
>> +	}
>>   	spin_unlock(&zone->lock);
>> +	__mod_zone_page_state(zone, NR_FREE_PAGES, free_ok<<  order);
>>   }
>>
>>   static void __free_pages_ok(struct page *page, unsigned int order)
>> -- 
>> 1.6.5.2
>>
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>>      
>
>    

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