From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail172.messagelabs.com (mail172.messagelabs.com [216.82.254.3]) by kanga.kvack.org (Postfix) with SMTP id 2BCCB6B02A4 for ; Thu, 22 Jul 2010 08:29:07 -0400 (EDT) Received: by pvc30 with SMTP id 30so3656641pvc.14 for ; Thu, 22 Jul 2010 05:29:08 -0700 (PDT) Date: Thu, 22 Jul 2010 21:28:42 +0900 From: Minchan Kim Subject: Re: [RFC]mm: batch activate_page() to reduce lock contention Message-ID: <20100722122842.GA23183@barrios-desktop> References: <1279610324.17101.9.camel@sli10-desk.sh.intel.com> <20100721160634.GA7976@barrios-desktop> <20100722002716.GA7740@sli10-desk.sh.intel.com> <20100722051702.GA26829@sli10-desk.sh.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20100722051702.GA26829@sli10-desk.sh.intel.com> Sender: owner-linux-mm@kvack.org To: Shaohua Li Cc: linux-mm , Andrew Morton , Andi Kleen , "Wu, Fengguang" List-ID: On Thu, Jul 22, 2010 at 01:17:03PM +0800, Shaohua Li wrote: > On Thu, Jul 22, 2010 at 09:08:43AM +0800, Minchan Kim wrote: > > On Thu, Jul 22, 2010 at 9:27 AM, Shaohua Li wrote: > > >> > But we did see some strange regression. The regression is small (usually < 2%) > > >> > and most are from multithread test and none heavily use activate_page(). For > > >> > example, in the same system, we create 64 threads. Each thread creates a private > > >> > mmap region and does read access. We measure the total time and saw about 2% > > >> > regression. But in such workload, 99% time is on page fault and activate_page() > > >> > takes no time. Very strange, we haven't a good explanation for this so far, > > >> > hopefully somebody can share a hint. > > >> > > >> Mabye it might be due to lru_add_drain. > > >> You are adding cost in lru_add_drain and it is called several place. > > >> So if we can't get the gain in there, it could make a bit of regression. > > >> I might be wrong and it's a just my guessing. > > > The workload with regression doesn't invoke too many activate_page, so > > > basically activate_page_drain_cpu() is a nop, it should not take too much. > > > > I think it's culprit. little call activate_page, many call lru_drain_all. > > It would make losing pagevec's benefit. > > But as your scenario, I think it doesn't call lru_drain_all frequently. > > That's because it is called when process call things related unmap > > operation or swapping. > > Do you have a such workload in test case? > Yes, I'm testing if activate_page_drain_cpu() causes the regression. This regression > is small (<2%) for a stress test and sometimes not stable. Do you mean regression is less 2% even corner case happens? Then, Okay. it might be marginal number. > > > >> > Signed-off-by: Shaohua Li > > >> > > > >> > diff --git a/mm/swap.c b/mm/swap.c > > >> > index 3ce7bc3..4a3fd7f 100644 > > >> > --- a/mm/swap.c > > >> > +++ b/mm/swap.c > > >> > @@ -39,6 +39,7 @@ int page_cluster; > > >> > > > >> > static DEFINE_PER_CPU(struct pagevec[NR_LRU_LISTS], lru_add_pvecs); > > >> > static DEFINE_PER_CPU(struct pagevec, lru_rotate_pvecs); > > >> > +static DEFINE_PER_CPU(struct pagevec, activate_page_pvecs); > > >> > > > >> > /* > > >> > * This path almost never happens for VM activity - pages are normally > > >> > @@ -175,11 +176,10 @@ static void update_page_reclaim_stat(struct zone *zone, struct page *page, > > >> > /* > > >> > * FIXME: speed this up? > > >> > */ > > >> Couldn't we remove above comment by this patch? > > > ha, yes. > > > > > >> > -void activate_page(struct page *page) > > >> > +static void __activate_page(struct page *page) > > >> > { > > >> > 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); > > >> > @@ -192,7 +192,46 @@ void activate_page(struct page *page) > > >> > > > >> > update_page_reclaim_stat(zone, page, file, 1); > > >> > } > > >> > - spin_unlock_irq(&zone->lru_lock); > > >> > +} > > >> > + > > >> > +static void activate_page_drain_cpu(int cpu) > > >> > +{ > > >> > + struct pagevec *pvec = &per_cpu(activate_page_pvecs, cpu); > > >> > + struct zone *last_zone = NULL, *zone; > > >> > + int i, j; > > >> > + > > >> > + for (i = 0; i < pagevec_count(pvec); i++) { > > >> > + zone = page_zone(pvec->pages[i]); > > >> > + if (zone == last_zone) > > >> > + continue; > > >> > + > > >> > + if (last_zone) > > >> > + spin_unlock_irq(&last_zone->lru_lock); > > >> > + last_zone = zone; > > >> > + spin_lock_irq(&last_zone->lru_lock); > > >> > + > > >> > + for (j = i; j < pagevec_count(pvec); j++) { > > >> > + struct page *page = pvec->pages[j]; > > >> > + > > >> > + if (last_zone != page_zone(page)) > > >> > + continue; > > >> > + __activate_page(page); > > >> > + } > > >> > + } > > >> > + if (last_zone) > > >> > + spin_unlock_irq(&last_zone->lru_lock); > > >> > + release_pages(pvec->pages, pagevec_count(pvec), pvec->cold); > > >> > + pagevec_reinit(pvec); > > >> > > >> In worst case(DMA->NORMAL->HIGHMEM->DMA->NORMA->HIGHMEM->......), > > >> overhead would is big than old. how about following as? > > >> static DEFINE_PER_CPU(struct pagevec[MAX_NR_ZONES], activate_page_pvecs); > > >> Is it a overkill? > > > activate_page_drain_cpu is a two level loop. In you case, the drain order > > > will be DMA->DMA->NORMAL->NORMAL->HIGHMEM->HIGHMEM. Since pagevec size is > > > 14, the loop should finish quickly. > > Yes. so why do we separates lru pagevec with pagevec[NR_LRU_LISTS]? > > I think It can remove looping unnecessary looping overhead but of > > course we have to use more memory. > Each node has zones, so a pagevec[MAX_NR_ZONES] doesn't work here. And in my Ahh. Yes. We might need pagevec per node but it seem to be overkill as you mentioned. Feel free to add my reviewed-by sign when you resend. Reviewed-by: Minchan Kim > test wich activate_page heavily used, activate_page_drain_cpu overhead is quite > small. This isn't worthy IMO. > > Thanks, > Shaohua -- Kind regards, Minchan Kim -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org