Re: [PATCH v3 3/6] mm/cma: populate ZONE_CMA

[Chen Feng]

Hello,

On 2016/6/23 10:52, Joonsoo Kim wrote:
> On Wed, Jun 22, 2016 at 05:23:06PM +0800, Chen Feng wrote:
>> Hello,
>>
>> On 2016/5/26 14:22, js1304@xxxxxxxxx wrote:
>>> From: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
>>>
>>> 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 <iamjoonsoo.kim@xxxxxxx>
>>> ---
>>>  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 <trace/events/cma.h>
>>>  
>>>  #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;
>>> +	}
>>> +
>>> +	/*
>>> +	 * 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);
>>>  
>>>  	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);
>>
>> The ZONE_CMA should depends on sparse_mem.
>>
>> Because the zone size is not fixed when init the buddy core.
>> The pageblock_flags will be NULL when setup_usemap.
> 
> Before setup_usemap(), range of ZONE_CMA is set conservatively, from
> min_start_pfn of the node to max_end_pfn of the node. So,
> pageblock_flags will be allocated and assigned properly.
> 
> Unfortunately, I found a bug for FLATMEM system. If you'd like to
> test ZONE_CMA on FLATMEM system, please apply below one.
> 

The filesystem, inode map is also GFP_HIGHUSER_MOVABLE.

SyS_write filemap_fault will also use cma memory.

This may also make cma migrate failed. What's your idea on this type?

> Thanks.
> ------------>8------------
> diff --git a/mm/cma.c b/mm/cma.c
> index 0c1a72f..6cd2973 100644
> --- a/mm/cma.c
> +++ b/mm/cma.c
> @@ -168,13 +168,6 @@ static int __init cma_init_reserved_areas(void)
>                 return 0;
>  
>         for (i = 0; i < cma_area_count; i++) {
> -               int ret = cma_activate_area(&cma_areas[i]);
> -
> -               if (ret)
> -                       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)
> @@ -191,6 +184,13 @@ static int __init cma_init_reserved_areas(void)
>                                         zone->zone_start_pfn;
>         }
>  
> +       for (i = 0; i < cma_area_count; i++) {
> +               int ret = cma_activate_area(&cma_areas[i]);
> +
> +               if (ret)
> +                       return ret;
> +       }
> +
>         /*
>          * Reserved pages for ZONE_CMA are now activated and this would change
>          * ZONE_CMA's managed page counter and other zone's present counter.
>