From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751873AbcF0IYN (ORCPT ); Mon, 27 Jun 2016 04:24:13 -0400 Received: from mx2.suse.de ([195.135.220.15]:46735 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751248AbcF0IYL (ORCPT ); Mon, 27 Jun 2016 04:24:11 -0400 Subject: Re: [PATCH v3 3/6] mm/cma: populate ZONE_CMA To: js1304@gmail.com, Andrew Morton References: <1464243748-16367-1-git-send-email-iamjoonsoo.kim@lge.com> <1464243748-16367-4-git-send-email-iamjoonsoo.kim@lge.com> Cc: Rik van Riel , Johannes Weiner , mgorman@techsingularity.net, Laura Abbott , Minchan Kim , Marek Szyprowski , Michal Nazarewicz , "Aneesh Kumar K.V" , Rui Teng , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Joonsoo Kim From: Vlastimil Babka Message-ID: <1919a85d-6e1e-374f-b8c3-1236c36b0393@suse.cz> Date: Mon, 27 Jun 2016 10:24:05 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.1.1 MIME-Version: 1.0 In-Reply-To: <1464243748-16367-4-git-send-email-iamjoonsoo.kim@lge.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/26/2016 08:22 AM, js1304@gmail.com wrote: > From: Joonsoo Kim > > Until now, reserved pages for CMA are managed in the ordinary zones > where page's pfn are belong to. This approach has numorous problems > and fixing them isn't easy. (It is mentioned on previous patch.) > To fix this situation, ZONE_CMA is introduced in previous patch, but, > not yet populated. This patch implement population of ZONE_CMA > by stealing reserved pages from the ordinary zones. > > Unlike previous implementation that kernel allocation request with > __GFP_MOVABLE could be serviced from CMA region, allocation request only > with GFP_HIGHUSER_MOVABLE can be serviced from CMA region in the new > approach. This is an inevitable design decision to use the zone > implementation because ZONE_CMA could contain highmem. Due to this > decision, ZONE_CMA will work like as ZONE_HIGHMEM or ZONE_MOVABLE. > > I don't think it would be a problem because most of file cache pages > and anonymous pages are requested with GFP_HIGHUSER_MOVABLE. It could > be proved by the fact that there are many systems with ZONE_HIGHMEM and > they work fine. Notable disadvantage is that we cannot use these pages > for blockdev file cache page, because it usually has __GFP_MOVABLE but > not __GFP_HIGHMEM and __GFP_USER. But, in this case, there is pros and > cons. In my experience, blockdev file cache pages are one of the top > reason that causes cma_alloc() to fail temporarily. So, we can get more > guarantee of cma_alloc() success by discarding that case. > > Implementation itself is very easy to understand. Steal when cma area is > initialized and recalculate various per zone stat/threshold. > > Signed-off-by: Joonsoo Kim I realize I differ here from much more experienced mm guys, and will probably deservingly regret it later on, but I think that the ZONE_CMA approach could work indeed better than current MIGRATE_CMA pageblocks. My main worry is (naturally :) the effect on compaction overhead, due to potentially sparsely populated zones with holes that have to be scanned over - either ZONE_CMA itself, or the zones where pages were stolen from. > --- > include/linux/memory_hotplug.h | 3 --- > mm/cma.c | 41 +++++++++++++++++++++++++++++++++++++++++ > mm/internal.h | 3 +++ > mm/page_alloc.c | 26 ++++++++++++++++++++++++-- > 4 files changed, 68 insertions(+), 5 deletions(-) > > diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h > index a864d79..6fde69b 100644 > --- a/include/linux/memory_hotplug.h > +++ b/include/linux/memory_hotplug.h > @@ -198,9 +198,6 @@ void put_online_mems(void); > void mem_hotplug_begin(void); > void mem_hotplug_done(void); > > -extern void set_zone_contiguous(struct zone *zone); > -extern void clear_zone_contiguous(struct zone *zone); > - > #else /* ! CONFIG_MEMORY_HOTPLUG */ > /* > * Stub functions for when hotplug is off > diff --git a/mm/cma.c b/mm/cma.c > index ea506eb..8684f50 100644 > --- a/mm/cma.c > +++ b/mm/cma.c > @@ -38,6 +38,7 @@ > #include > > #include "cma.h" > +#include "internal.h" > > struct cma cma_areas[MAX_CMA_AREAS]; > unsigned cma_area_count; > @@ -145,6 +146,11 @@ err: > static int __init cma_init_reserved_areas(void) > { > int i; > + struct zone *zone; > + unsigned long start_pfn = UINT_MAX, end_pfn = 0; > + > + if (!cma_area_count) > + return 0; > > for (i = 0; i < cma_area_count; i++) { > int ret = cma_activate_area(&cma_areas[i]); > @@ -153,6 +159,41 @@ static int __init cma_init_reserved_areas(void) > return ret; > } > > + for (i = 0; i < cma_area_count; i++) { > + if (start_pfn > cma_areas[i].base_pfn) > + start_pfn = cma_areas[i].base_pfn; > + if (end_pfn < cma_areas[i].base_pfn + cma_areas[i].count) > + end_pfn = cma_areas[i].base_pfn + cma_areas[i].count; > + } > + > + for_each_populated_zone(zone) { > + if (!is_zone_cma(zone)) > + continue; > + > + /* ZONE_CMA doesn't need to exceed CMA region */ > + zone->zone_start_pfn = max(zone->zone_start_pfn, start_pfn); > + zone->spanned_pages = min(zone_end_pfn(zone), end_pfn) - > + zone->zone_start_pfn; So what's the typical spanned vs present pages here? Should there perhaps be some pr_warns about large holes? > + } > + > + /* > + * Reserved pages for ZONE_CMA are now activated and this would change > + * ZONE_CMA's managed page counter and other zone's present counter. > + * We need to re-calculate various zone information that depends on > + * this initialization. > + */ > + build_all_zonelists(NULL, NULL); > + for_each_populated_zone(zone) { > + zone_pcp_update(zone); > + set_zone_contiguous(zone); > + } > + > + /* > + * We need to re-init per zone wmark by calling > + * init_per_zone_wmark_min() but doesn't call here because it is > + * registered on module_init and it will be called later than us. > + */ > + > return 0; > } > core_initcall(cma_init_reserved_areas); > diff --git a/mm/internal.h b/mm/internal.h > index b6ead95..4c37234 100644 > --- a/mm/internal.h > +++ b/mm/internal.h > @@ -155,6 +155,9 @@ extern void __free_pages_bootmem(struct page *page, unsigned long pfn, > extern void prep_compound_page(struct page *page, unsigned int order); > extern int user_min_free_kbytes; > > +extern void set_zone_contiguous(struct zone *zone); > +extern void clear_zone_contiguous(struct zone *zone); > + > #if defined CONFIG_COMPACTION || defined CONFIG_CMA > > /* > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 0197d5d..796b271 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -1572,16 +1572,38 @@ void __init page_alloc_init_late(void) > } > > #ifdef CONFIG_CMA > +static void __init adjust_present_page_count(struct page *page, long count) > +{ > + struct zone *zone = page_zone(page); > + > + /* We don't need to hold a lock since it is boot-up process */ > + zone->present_pages += count; > +} > + > /* Free whole pageblock and set its migration type to MIGRATE_CMA. */ > void __init init_cma_reserved_pageblock(struct page *page) > { > unsigned i = pageblock_nr_pages; > + unsigned long pfn = page_to_pfn(page); > struct page *p = page; > + int nid = page_to_nid(page); > + > + /* > + * ZONE_CMA will steal present pages from other zones by changing > + * page links so page_zone() is changed. Before that, > + * we need to adjust previous zone's page count first. > + */ > + adjust_present_page_count(page, -pageblock_nr_pages); Ideally, zone's start_pfn and spanned_pages should be also adjusted if we stole from the beginning/end (which I suppose should be quite common?). BTW, shouldn't it be possible with ZONE_CMA to drop the requirement in cma_activate_area() that all pages come (originally) from the same zone, after your series? > > do { > __ClearPageReserved(p); > set_page_count(p, 0); > - } while (++p, --i); > + > + /* Steal pages from other zones */ > + set_page_links(p, ZONE_CMA, nid, pfn); > + } while (++p, ++pfn, --i); > + > + adjust_present_page_count(page, pageblock_nr_pages); > > set_pageblock_migratetype(page, MIGRATE_CMA); > > @@ -7545,7 +7567,7 @@ void free_contig_range(unsigned long pfn, unsigned nr_pages) > } > #endif > > -#ifdef CONFIG_MEMORY_HOTPLUG > +#if defined CONFIG_MEMORY_HOTPLUG || defined CONFIG_CMA > /* > * The zone indicated has a new number of managed_pages; batch sizes and percpu > * page high values need to be recalulated. >