From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752597AbaEMC6i (ORCPT ); Mon, 12 May 2014 22:58:38 -0400 Received: from lgeamrelo02.lge.com ([156.147.1.126]:42828 "EHLO lgeamrelo02.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751829AbaEMC6h (ORCPT ); Mon, 12 May 2014 22:58:37 -0400 X-Original-SENDERIP: 10.177.220.169 X-Original-MAILFROM: minchan.kim@lge.com Date: Tue, 13 May 2014 12:00:57 +0900 From: Minchan Kim To: Joonsoo Kim Cc: Andrew Morton , Rik van Riel , Laura Abbott , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Michal Nazarewicz , Heesub Shin , Mel Gorman , Johannes Weiner , Marek Szyprowski Subject: Re: [RFC PATCH 2/3] CMA: aggressively allocate the pages on cma reserved memory when not used Message-ID: <20140513030057.GC32092@bbox> References: <1399509144-8898-1-git-send-email-iamjoonsoo.kim@lge.com> <1399509144-8898-3-git-send-email-iamjoonsoo.kim@lge.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1399509144-8898-3-git-send-email-iamjoonsoo.kim@lge.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hey Joonsoo, On Thu, May 08, 2014 at 09:32:23AM +0900, Joonsoo Kim wrote: > CMA is introduced to provide physically contiguous pages at runtime. > For this purpose, it reserves memory at boot time. Although it reserve > memory, this reserved memory can be used for movable memory allocation > request. This usecase is beneficial to the system that needs this CMA > reserved memory infrequently and it is one of main purpose of > introducing CMA. > > But, there is a problem in current implementation. The problem is that > it works like as just reserved memory approach. The pages on cma reserved > memory are hardly used for movable memory allocation. This is caused by > combination of allocation and reclaim policy. > > The pages on cma reserved memory are allocated if there is no movable > memory, that is, as fallback allocation. So the time this fallback > allocation is started is under heavy memory pressure. Although it is under > memory pressure, movable allocation easily succeed, since there would be > many pages on cma reserved memory. But this is not the case for unmovable > and reclaimable allocation, because they can't use the pages on cma > reserved memory. These allocations regard system's free memory as > (free pages - free cma pages) on watermark checking, that is, free > unmovable pages + free reclaimable pages + free movable pages. Because > we already exhausted movable pages, only free pages we have are unmovable > and reclaimable types and this would be really small amount. So watermark > checking would be failed. It will wake up kswapd to make enough free > memory for unmovable and reclaimable allocation and kswapd will do. > So before we fully utilize pages on cma reserved memory, kswapd start to > reclaim memory and try to make free memory over the high watermark. This > watermark checking by kswapd doesn't take care free cma pages so many > movable pages would be reclaimed. After then, we have a lot of movable > pages again, so fallback allocation doesn't happen again. To conclude, > amount of free memory on meminfo which includes free CMA pages is moving > around 512 MB if I reserve 512 MB memory for CMA. > > I found this problem on following experiment. > > 4 CPUs, 1024 MB, VIRTUAL MACHINE > make -j24 > > CMA reserve: 0 MB 512 MB > Elapsed-time: 234.8 361.8 > Average-MemFree: 283880 KB 530851 KB > > To solve this problem, I can think following 2 possible solutions. > 1. allocate the pages on cma reserved memory first, and if they are > exhausted, allocate movable pages. > 2. interleaved allocation: try to allocate specific amounts of memory > from cma reserved memory and then allocate from free movable memory. I love this idea but when I see the code, I don't like that. In allocation path, just try to allocate pages by round-robin so it's role of allocator. If one of migratetype is full, just pass mission to reclaimer with hint(ie, Hey reclaimer, it's non-movable allocation fail so there is pointless if you reclaim MIGRATE_CMA pages) so that reclaimer can filter it out during page scanning. We already have an tool to achieve it(ie, isolate_mode_t). And we couldn't do it in zone_watermark_ok with set/reset ALLOC_CMA? If possible, it would be better becauser it's generic function to check free pages and cause trigger reclaim/compaction logic. > > I tested #1 approach and found the problem. Although free memory on > meminfo can move around low watermark, there is large fluctuation on free > memory, because too many pages are reclaimed when kswapd is invoked. > Reason for this behaviour is that successive allocated CMA pages are > on the LRU list in that order and kswapd reclaim them in same order. > These memory doesn't help watermark checking from kwapd, so too many > pages are reclaimed, I guess. > > So, I implement #2 approach. > One thing I should note is that we should not change allocation target > (movable list or cma) on each allocation attempt, since this prevent > allocated pages to be in physically succession, so some I/O devices can > be hurt their performance. To solve this, I keep allocation target > in at least pageblock_nr_pages attempts and make this number reflect > ratio, free pages without free cma pages to free cma pages. With this > approach, system works very smoothly and fully utilize the pages on > cma reserved memory. > > Following is the experimental result of this patch. > > 4 CPUs, 1024 MB, VIRTUAL MACHINE > make -j24 > > > CMA reserve: 0 MB 512 MB > Elapsed-time: 234.8 361.8 > Average-MemFree: 283880 KB 530851 KB > pswpin: 7 110064 > pswpout: 452 767502 > > > CMA reserve: 0 MB 512 MB > Elapsed-time: 234.2 235.6 > Average-MemFree: 281651 KB 290227 KB > pswpin: 8 8 > pswpout: 430 510 > > There is no difference if we don't have cma reserved memory (0 MB case). > But, with cma reserved memory (512 MB case), we fully utilize these > reserved memory through this patch and the system behaves like as > it doesn't reserve any memory. > > With this patch, we aggressively allocate the pages on cma reserved memory > so latency of CMA can arise. Below is the experimental result about > latency. > > 4 CPUs, 1024 MB, VIRTUAL MACHINE > CMA reserve: 512 MB > Backgound Workload: make -jN > Real Workload: 8 MB CMA allocation/free 20 times with 5 sec interval > > N: 1 4 8 16 > Elapsed-time(Before): 4309.75 9511.09 12276.1 77103.5 > Elapsed-time(After): 5391.69 16114.1 19380.3 34879.2 > > So generally we can see latency increase. Ratio of this increase > is rather big - up to 70%. But, under the heavy workload, it shows > latency decrease - up to 55%. This may be worst-case scenario, but > reducing it would be important for some system, so, I can say that > this patch have advantages and disadvantages in terms of latency. > > Signed-off-by: Joonsoo Kim > > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h > index fac5509..3ff24d4 100644 > --- a/include/linux/mmzone.h > +++ b/include/linux/mmzone.h > @@ -389,6 +389,12 @@ struct zone { > int compact_order_failed; > #endif > > +#ifdef CONFIG_CMA > + int has_cma; > + int nr_try_cma; > + int nr_try_movable; > +#endif > + > ZONE_PADDING(_pad1_) > > /* Fields commonly accessed by the page reclaim scanner */ > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 674ade7..6f2b27b 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -788,6 +788,16 @@ void __init __free_pages_bootmem(struct page *page, unsigned int order) > } > > #ifdef CONFIG_CMA > +void __init init_alloc_ratio_counter(struct zone *zone) > +{ > + if (zone->has_cma) > + return; > + > + zone->has_cma = 1; > + zone->nr_try_movable = 0; > + zone->nr_try_cma = 0; > +} > + > /* Free whole pageblock and set its migration type to MIGRATE_CMA. */ > void __init init_cma_reserved_pageblock(struct page *page) > { > @@ -803,6 +813,7 @@ void __init init_cma_reserved_pageblock(struct page *page) > set_pageblock_migratetype(page, MIGRATE_CMA); > __free_pages(page, pageblock_order); > adjust_managed_page_count(page, pageblock_nr_pages); > + init_alloc_ratio_counter(page_zone(page)); > } > #endif > > @@ -1136,6 +1147,69 @@ __rmqueue_fallback(struct zone *zone, int order, int start_migratetype) > return NULL; > } > > +#ifdef CONFIG_CMA > +static struct page *__rmqueue_cma(struct zone *zone, unsigned int order, > + int migratetype) > +{ > + long free, free_cma, free_wmark; > + struct page *page; > + > + if (migratetype != MIGRATE_MOVABLE || !zone->has_cma) > + return NULL; > + > + if (zone->nr_try_movable) > + goto alloc_movable; > + > +alloc_cma: > + if (zone->nr_try_cma) { > + /* Okay. Now, we can try to allocate the page from cma region */ > + zone->nr_try_cma--; > + page = __rmqueue_smallest(zone, order, MIGRATE_CMA); > + > + /* CMA pages can vanish through CMA allocation */ > + if (unlikely(!page && order == 0)) > + zone->nr_try_cma = 0; > + > + return page; > + } > + > + /* Reset ratio counter */ > + free_cma = zone_page_state(zone, NR_FREE_CMA_PAGES); > + > + /* No cma free pages, so recharge only movable allocation */ > + if (free_cma <= 0) { > + zone->nr_try_movable = pageblock_nr_pages; > + goto alloc_movable; > + } > + > + free = zone_page_state(zone, NR_FREE_PAGES); > + free_wmark = free - free_cma - high_wmark_pages(zone); > + > + /* > + * free_wmark is below than 0, and it means that normal pages > + * are under the pressure, so we recharge only cma allocation. > + */ > + if (free_wmark <= 0) { > + zone->nr_try_cma = pageblock_nr_pages; > + goto alloc_cma; > + } > + > + if (free_wmark > free_cma) { > + zone->nr_try_movable = > + (free_wmark * pageblock_nr_pages) / free_cma; > + zone->nr_try_cma = pageblock_nr_pages; > + } else { > + zone->nr_try_movable = pageblock_nr_pages; > + zone->nr_try_cma = free_cma * pageblock_nr_pages / free_wmark; > + } > + > + /* Reset complete, start on movable first */ > +alloc_movable: > + zone->nr_try_movable--; > + return NULL; > +} > +#endif > + > /* > * Do the hard work of removing an element from the buddy allocator. > * Call me with the zone->lock already held. > @@ -1143,10 +1217,14 @@ __rmqueue_fallback(struct zone *zone, int order, int start_migratetype) > static struct page *__rmqueue(struct zone *zone, unsigned int order, > int migratetype) > { > - struct page *page; > + struct page *page = NULL; > + > + if (IS_ENABLED(CONFIG_CMA)) > + page = __rmqueue_cma(zone, order, migratetype); > > retry_reserve: > - page = __rmqueue_smallest(zone, order, migratetype); > + if (!page) > + page = __rmqueue_smallest(zone, order, migratetype); > > if (unlikely(!page) && migratetype != MIGRATE_RESERVE) { > page = __rmqueue_fallback(zone, order, migratetype); > @@ -4849,6 +4927,8 @@ static void __paginginit free_area_init_core(struct pglist_data *pgdat, > zone_seqlock_init(zone); > zone->zone_pgdat = pgdat; > zone_pcp_init(zone); > + if (IS_ENABLED(CONFIG_CMA)) > + zone->has_cma = 0; > > /* For bootup, initialized properly in watermark setup */ > mod_zone_page_state(zone, NR_ALLOC_BATCH, zone->managed_pages); > -- > 1.7.9.5 > > _______________________________________________ > OTC mailing list > OTC@blackduck.lge.com > http://blackduck.lge.com/mailman/listinfo/otc -- Kind regards, Minchan Kim