Re: [PATCH v2 5/7] mm: munlock: bypass per-cpu pvec for putback_lru_page

[Vlastimil Babka <vbabka@suse.cz>]

On 08/20/2013 12:45 AM, Andrew Morton wrote:
> On Mon, 19 Aug 2013 14:23:40 +0200 Vlastimil Babka <vbabka@suse.cz> wrote:
> 
>> After introducing batching by pagevecs into munlock_vma_range(), we can further
>> improve performance by bypassing the copying into per-cpu pagevec and the
>> get_page/put_page pair associated with that. Instead we perform LRU putback
>> directly from our pagevec. However, this is possible only for single-mapped
>> pages that are evictable after munlock. Unevictable pages require rechecking
>> after putting on the unevictable list, so for those we fallback to
>> putback_lru_page(), hich handles that.
>>
>> After this patch, a 13% speedup was measured for munlocking a 56GB large memory
>> area with THP disabled.
>>
>> ...
>>
>> +static void __putback_lru_fast(struct pagevec *pvec, int pgrescued)
>> +{
>> +	count_vm_events(UNEVICTABLE_PGMUNLOCKED, pagevec_count(pvec));
>> +	/* This includes put_page so we don't call it explicitly */
> 
> This had me confused for a sec.  __pagevec_lru_add() includes put_page,
> so we don't call __pagevec_lru_add()?  That's the problem with the word
> "it" - one often doesn't know what it refers to.
> 
> Clarity: 
> 
> --- a/mm/mlock.c~mm-munlock-bypass-per-cpu-pvec-for-putback_lru_page-fix
> +++ a/mm/mlock.c
> @@ -264,7 +264,10 @@ static bool __putback_lru_fast_prepare(s
>  static void __putback_lru_fast(struct pagevec *pvec, int pgrescued)
>  {
>  	count_vm_events(UNEVICTABLE_PGMUNLOCKED, pagevec_count(pvec));
> -	/* This includes put_page so we don't call it explicitly */
> +	/*
> +	 *__pagevec_lru_add() calls release_pages() so we don't call
> +	 * put_page() explicitly
> +	 */
>  	__pagevec_lru_add(pvec);
>  	count_vm_events(UNEVICTABLE_PGRESCUED, pgrescued);
>  }

Yes this is definitely better, thanks.

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