Re: [PATCH 2/2 v4]mm: batch activate_page() to reduce lock contention

[Minchan Kim <minchan.kim@gmail.com>]

On Thu, Mar 10, 2011 at 01:30:19PM +0800, Shaohua Li wrote:
> The zone->lru_lock is heavily contented in workload where activate_page()
> is frequently used. We could do batch activate_page() to reduce the lock
> contention. The batched pages will be added into zone list when the pool
> is full or page reclaim is trying to drain them.
> 
> For example, in a 4 socket 64 CPU system, create a sparse file and 64 processes,
> processes shared map to the file. Each process read access the whole file and
> then exit. The process exit will do unmap_vmas() and cause a lot of
> activate_page() call. In such workload, we saw about 58% total time reduction
> with below patch. Other workloads with a lot of activate_page also benefits a
> lot too.
> 
> Andrew Morton suggested activate_page() and putback_lru_pages() should
> follow the same path to active pages, but this is hard to implement (see commit
> 7a608572a282a). On the other hand, do we really need putback_lru_pages() to
> follow the same path? I tested several FIO/FFSB benchmark (about 20 scripts for
> each benchmark) in 3 machines here from 2 sockets to 4 sockets. My test doesn't
> show anything significant with/without below patch (there is slight difference
> but mostly some noise which we found even without below patch before). Below
> patch basically returns to the same as my first post.
> 
> I tested some microbenchmarks:
> case-anon-cow-rand-mt               0.58%
> case-anon-cow-rand          -3.30%
> case-anon-cow-seq-mt                -0.51%
> case-anon-cow-seq           -5.68%
> case-anon-r-rand-mt         0.23%
> case-anon-r-rand            0.81%
> case-anon-r-seq-mt          -0.71%
> case-anon-r-seq                     -1.99%
> case-anon-rx-rand-mt                2.11%
> case-anon-rx-seq-mt         3.46%
> case-anon-w-rand-mt         -0.03%
> case-anon-w-rand            -0.50%
> case-anon-w-seq-mt          -1.08%
> case-anon-w-seq                     -0.12%
> case-anon-wx-rand-mt                -5.02%
> case-anon-wx-seq-mt         -1.43%
> case-fork                   1.65%
> case-fork-sleep                     -0.07%
> case-fork-withmem           1.39%
> case-hugetlb                        -0.59%
> case-lru-file-mmap-read-mt  -0.54%
> case-lru-file-mmap-read             0.61%
> case-lru-file-mmap-read-rand        -2.24%
> case-lru-file-readonce              -0.64%
> case-lru-file-readtwice             -11.69%
> case-lru-memcg                      -1.35%
> case-mmap-pread-rand-mt             1.88%
> case-mmap-pread-rand                -15.26%
> case-mmap-pread-seq-mt              0.89%
> case-mmap-pread-seq         -69.72%
> case-mmap-xread-rand-mt             0.71%
> case-mmap-xread-seq-mt              0.38%
> 
> The most significent are:
> case-lru-file-readtwice             -11.69%
> case-mmap-pread-rand                -15.26%
> case-mmap-pread-seq         -69.72%
> 
> which use activate_page a lot.  others are basically variations because
> each run has slightly difference.
> 
> In UP case, 'size mm/swap.o'
> before the two patches:
>    text    data     bss     dec     hex filename
>    6466     896       4    7366    1cc6 mm/swap.o
> after the two patches:
>    text    data     bss     dec     hex filename
>    6343     896       4    7243    1c4b mm/swap.o
> 
> Signed-off-by: Shaohua Li <shaohua.li@intel.com>
> 
> ---
>  mm/swap.c |   45 ++++++++++++++++++++++++++++++++++++++++-----
>  1 file changed, 40 insertions(+), 5 deletions(-)
> 
> Index: linux/mm/swap.c
> ===================================================================
> --- linux.orig/mm/swap.c	2011-03-09 12:56:09.000000000 +0800
> +++ linux/mm/swap.c	2011-03-09 12:56:46.000000000 +0800
> @@ -272,14 +272,10 @@ static void update_page_reclaim_stat(str
>  		memcg_reclaim_stat->recent_rotated[file]++;
>  }
>  
> -/*
> - * FIXME: speed this up?
> - */
> -void activate_page(struct page *page)
> +static void __activate_page(struct page *page, void *arg)
>  {
>  	struct zone *zone = page_zone(page);
>  
> -	spin_lock_irq(&zone->lru_lock);
>  	if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
>  		int file = page_is_file_cache(page);
>  		int lru = page_lru_base_type(page);
> @@ -292,8 +288,45 @@ void activate_page(struct page *page)
>  
>  		update_page_reclaim_stat(zone, page, file, 1);
>  	}
> +}
> +
> +#ifdef CONFIG_SMP
> +static DEFINE_PER_CPU(struct pagevec, activate_page_pvecs);
> +
> +static void activate_page_drain(int cpu)
> +{
> +	struct pagevec *pvec = &per_cpu(activate_page_pvecs, cpu);
> +
> +	if (pagevec_count(pvec))
> +		pagevec_lru_move_fn(pvec, __activate_page, NULL);
> +}
> +
> +void activate_page(struct page *page)
> +{
> +	if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
> +		struct pagevec *pvec = &get_cpu_var(activate_page_pvecs);
> +
> +		page_cache_get(page);
> +		if (!pagevec_add(pvec, page))
> +			pagevec_lru_move_fn(pvec, __activate_page, NULL);
> +		put_cpu_var(activate_page_pvecs);
> +	}
> +}
> +
> +#else
> +static inline void activate_page_drain(int cpu)
> +{
> +}
> +
> +void activate_page(struct page *page)
> +{
> +	struct zone *zone = page_zone(page);
> +
> +	spin_lock_irq(&zone->lru_lock);
> +	__activate_page(page, NULL);
>  	spin_unlock_irq(&zone->lru_lock);
>  }
> +#endif
 
Why do we need CONFIG_SMP in only activate_page_pvecs?
The per-cpu of activate_page_pvecs consumes lots of memory in UP?
I don't think so. But if it consumes lots of memory, it's a problem
of per-cpu. 

I can't understand why we should hanlde activate_page_pvecs specially.
Please, enlighten me. 

-- 
Kind regards,
Minchan Kim

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