linux-kernel - Re: [RFC 00/16] Introduce ZONE

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Date:	Thu, 05 Mar 2015 18:48:50 +0100
From:	Vlastimil Babka <vbabka@...e.cz>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Andrew Morton <akpm@...ux-foundation.org>
CC:	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Mel Gorman <mgorman@...e.de>,
	Laura Abbott <lauraa@...eaurora.org>,
	Minchan Kim <minchan@...nel.org>,
	Heesub Shin <heesub.shin@...sung.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Michal Nazarewicz <mina86@...a86.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Hui Zhu <zhuhui@...omi.com>, Gioh Kim <gioh.kim@....com>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Ritesh Harjani <ritesh.list@...il.com>
Subject: Re: [RFC 00/16] Introduce ZONE_CMA

On 03/05/2015 05:53 PM, Vlastimil Babka wrote:
> On 02/12/2015 08:32 AM, Joonsoo Kim wrote:
>> 
>> 1) Break non-overlapped zone assumption
>> CMA regions could be spread to all memory range, so, to keep all of them
>> into one zone, span of ZONE_CMA would be overlap to other zones'.
> 
> From patch 13/16 ut seems to me that indeed the ZONE_CMA spans the area of all
> other zones. This seems very inefficient for e.g. compaction scanners, which
> will repeatedly skip huge amounts of pageblocks that don't belong to ZONE_CMA.
> Could you instead pick only a single zone on a node from which you steal the
> pages? That would allow to keep the span low.
> 
> Another disadvantage I see is that to allocate from ZONE_CMA you will have now
> to reclaim enough pages within the zone itself. I think think the cma allocation

                                                  I don't think...

> supports migrating pages from ZONE_CMA to the adjacent non-CMA zone, which would
> be equivalent to migration from MIGRATE_CMA pageblocks to the rest of the zone?
> 
>> I'm not sure that there is an assumption about possibility of zone overlap
>> But, if ZONE_CMA is introduced, this assumption becomes reality
>> so we should deal with this situation. I investigated most of sites
>> that iterates pfn on certain zone and found that they normally doesn't
>> consider zone overlap. I tried to handle these cases by myself in the
>> early of this series. I hope that there is no more site that depends on
>> non-overlap zone assumption when iterating pfn on certain zone.
>> 
>> I passed boot test on x86, ARM32 and ARM64. I did some stress tests
>> on x86 and there is no problem. Feel free to enjoy and please give me
>> a feedback. :)
>> 
>> This patchset is based on v3.18.
>> 
>> Thanks.
>> 
>> [1] https://lkml.org/lkml/2014/5/28/64
>> [2] https://lkml.org/lkml/2014/11/4/55 
>> [3] https://lkml.org/lkml/2014/10/15/623
>> [4] https://lkml.org/lkml/2014/5/30/320
>> 
>> 
>> Joonsoo Kim (16):
>>   mm/page_alloc: correct highmem memory statistics
>>   mm/writeback: correct dirty page calculation for highmem
>>   mm/highmem: make nr_free_highpages() handles all highmem zones by
>>     itself
>>   mm/vmstat: make node_page_state() handles all zones by itself
>>   mm/vmstat: watch out zone range overlap
>>   mm/page_alloc: watch out zone range overlap
>>   mm/page_isolation: watch out zone range overlap
>>   power: watch out zone range overlap
>>   mm/cma: introduce cma_total_pages() for future use
>>   mm/highmem: remove is_highmem_idx()
>>   mm/page_alloc: clean-up free_area_init_core()
>>   mm/cma: introduce new zone, ZONE_CMA
>>   mm/cma: populate ZONE_CMA and use this zone when GFP_HIGHUSERMOVABLE
>>   mm/cma: print stealed page count
>>   mm/cma: remove ALLOC_CMA
>>   mm/cma: remove MIGRATE_CMA
>> 
>>  arch/x86/include/asm/sparsemem.h  |    2 +-
>>  arch/x86/mm/highmem_32.c          |    3 +
>>  include/linux/cma.h               |    9 ++
>>  include/linux/gfp.h               |   31 +++---
>>  include/linux/mempolicy.h         |    2 +-
>>  include/linux/mm.h                |    1 +
>>  include/linux/mmzone.h            |   58 +++++-----
>>  include/linux/page-flags-layout.h |    2 +
>>  include/linux/vm_event_item.h     |    8 +-
>>  include/linux/vmstat.h            |   26 +----
>>  kernel/power/snapshot.c           |   15 +++
>>  lib/show_mem.c                    |    2 +-
>>  mm/cma.c                          |   70 ++++++++++--
>>  mm/compaction.c                   |    6 +-
>>  mm/highmem.c                      |   12 +-
>>  mm/hugetlb.c                      |    2 +-
>>  mm/internal.h                     |    3 +-
>>  mm/memory_hotplug.c               |    3 +
>>  mm/mempolicy.c                    |    3 +-
>>  mm/page-writeback.c               |    8 +-
>>  mm/page_alloc.c                   |  223 +++++++++++++++++++++----------------
>>  mm/page_isolation.c               |   14 ++-
>>  mm/vmscan.c                       |    2 +-
>>  mm/vmstat.c                       |   16 ++-
>>  24 files changed, 317 insertions(+), 204 deletions(-)
>> 
> 
> --
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