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

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Mon, 11 Jan 2010 15:38:02 +0900
Minchan Kim <minchan.kim@gmail.com> wrote:

> On Mon, 11 Jan 2010 14:27:57 +0800
> Huang Shijie <shijie8@gmail.com> wrote:
> 
> >   Move the __mod_zone_page_state out the guard region of
> > the spinlock to relieve the pressure for memory free.
> > 
> >   Using the zone->lru_lock to replace the zone->lock for
> > zone->pages_scanned and zone's flag ZONE_ALL_UNRECLAIMABLE.
> > 
> > Signed-off-by: Huang Shijie <shijie8@gmail.com>
> > ---
> >  mm/page_alloc.c |   33 +++++++++++++++++++++++----------
> >  1 files changed, 23 insertions(+), 10 deletions(-)
> > 
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 290dfc3..dfd4be0 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;
> > -
> > -	__mod_zone_page_state(zone, NR_FREE_PAGES, count);
> >  	while (count) {
> >  		struct page *page;
> >  		struct list_head *list;
> > @@ -558,23 +555,39 @@ 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));
> >  	}
> >  	spin_unlock(&zone->lock);
> > +
> > +	if (likely(free_ok)) {
> > +		spin_lock(&zone->lru_lock);
> > +		zone_clear_flag(zone, ZONE_ALL_UNRECLAIMABLE);
> > +		zone->pages_scanned = 0;
> > +		spin_unlock(&zone->lru_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);
> >  	spin_unlock(&zone->lock);
> > +
> > +	if (likely(free_ok)) {
> > +		spin_lock(&zone->lru_lock);
> > +		zone_clear_flag(zone, ZONE_ALL_UNRECLAIMABLE);
> > +		zone->pages_scanned = 0;
> > +		spin_unlock(&zone->lru_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
> > 
> 
> Thanks, Huang. 
> 
> Frankly speaking, I am not sure this ir right way.
> This patch is adding to fine-grained locking overhead
> 
> As you know, this functions are one of hot pathes.
> In addition, we didn't see the any problem, until now.
> It means out of synchronization in ZONE_ALL_UNRECLAIMABLE 
> and pages_scanned are all right?
> 
> If it is, we can move them out of zone->lock, too.
> If it isn't, we need one more lock, then. 
> 
I don't want to see additional spin_lock, here. 

About ZONE_ALL_UNRECLAIMABLE, it's not necessary to be handled in atomic way.
If you have concerns with other flags, please modify this with single word,
instead of a bit field.

Thanks,
-Kame









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