Re: [RFC PATCH] mm: fix up zone's present_pages

[Jiang Liu <jiang.liu@huawei.com>]

On 2012-11-19 16:45, Bob Liu wrote:
> zone->present_pages shoule be:
> spanned pages - absent pages - bootmem pages(including memmap pages),
> but now it's:
> spanned pages - absent pages - memmap pages.
> And it didn't consider whether the memmap pages is actully allocated from the
> zone or not which may cause problem when memory hotplug is improved recently.
> 
> For example:
> numa node 1 has ZONE_NORMAL and ZONE_MOVABLE, it's memmap and other bootmem
> allocated from ZONE_MOVABLE.
> So ZONE_NORMAL's present_pages should be spanned pages - absent pages, but now
> it also minus memmap pages, which are actually allocated from ZONE_MOVABLE.
> This is wrong and when offlining all memory of this zone:
> (zone->present_pages -= offline_pages) will less than 0.
> Since present_pages is unsigned long type, that is actually a very large
> integer which will cause zone->watermark[WMARK_MIN] becomes a large
> integer too(see setup_per_zone_wmarks()).
> As a result, totalreserve_pages become a large integer also and finally memory
> allocating will fail in __vm_enough_memory().
> 
> Related discuss:
> http://lkml.org/lkml/2012/11/5/866
> https://patchwork.kernel.org/patch/1346751/
> 
> Related patches in mmotm:
> mm: fix-up zone present pages(7f1290f2f2a4d2c) (sometimes cause egression)
> mm: fix a regression with HIGHMEM(fe2cebd5a259eec) (Andrew have some feedback)
> 
> Jiang Liu have sent a series patches to fix this issue by adding a
> managed_pages area to zone struct:
> [RFT PATCH v1 0/5] fix up inaccurate zone->present_pages
> 
> But i think it's too complicated.
> Mine is based on the two related patches already in mmotm(need to revert them
> first)
> It fix the calculation of zone->present_pages by:
> 1. Reset the zone->present_pages to zero before
> free_all_bootmem(),free_all_bootmem_node() and free_low_memory_core_early().
> I think these should already included all path in all arch.
> 
> 2. If there is a page freed to buddy system in __free_pages_bootmem(),
> add zone->present_pages accrodingly.
> 
> Note this patch assumes that bootmem won't use memory above ZONE_HIGHMEM, so
> only zones below ZONE_HIGHMEM are reset/fixed. If not, some update is needed.
> For ZONE_HIGHMEM, only fix it's init value to:
> panned_pages - absent_pages in free_area_init_core().
> 
> Only did some simple test currently.
Hi Bobi 1/4 ?
	Great to know that you are working on this issue too.
Originally I have thought about reusing the zone->present_pages.
And later I propose to add the new field "managed_pages" because
we could know that there are some pages not managed by the buddy
system in the zone (present_pages - managed_pages). This may help
the ongoing memory power management work from Srivatsa S. Bhat
because we can't put memory ranges into low power state if there
are unmanaged pages.
And pgdat->node_present_pages = spanned_pages - absent_pages,
so it would be better to keep consistence with node_present_pages
by setting zone->present_pages = spanned_pages - absent_pages.
	Thanks!
	Gerry

> 
> Signed-off-by: Jianguo Wu <wujianguo@huawei.com>
> Signed-off-by: Jiang Liu <jiang.liu@huawei.com>
> Signed-off-by: Bob Liu <lliubbo@gmail.com>
> ---
>  include/linux/mm.h |    3 +++
>  mm/bootmem.c       |    2 ++
>  mm/nobootmem.c     |    1 +
>  mm/page_alloc.c    |   49 +++++++++++++++++++++++++++++++++++++------------
>  4 files changed, 43 insertions(+), 12 deletions(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 7b03cab..3b40eb6 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1763,5 +1763,8 @@ static inline unsigned int debug_guardpage_minorder(void) { return 0; }
>  static inline bool page_is_guard(struct page *page) { return false; }
>  #endif /* CONFIG_DEBUG_PAGEALLOC */
>  
> +extern void reset_lowmem_zone_present_pages_pernode(pg_data_t *pgdat);
> +extern void reset_lowmem_zone_present_pages(void);
> +
>  #endif /* __KERNEL__ */
>  #endif /* _LINUX_MM_H */
> diff --git a/mm/bootmem.c b/mm/bootmem.c
> index 26d057a..661775b 100644
> --- a/mm/bootmem.c
> +++ b/mm/bootmem.c
> @@ -238,6 +238,7 @@ static unsigned long __init free_all_bootmem_core(bootmem_data_t *bdata)
>  unsigned long __init free_all_bootmem_node(pg_data_t *pgdat)
>  {
>  	register_page_bootmem_info_node(pgdat);
> +	reset_lowmem_zone_present_pages_pernode(pgdat);
>  	return free_all_bootmem_core(pgdat->bdata);
>  }
>  
> @@ -251,6 +252,7 @@ unsigned long __init free_all_bootmem(void)
>  	unsigned long total_pages = 0;
>  	bootmem_data_t *bdata;
>  
> +	reset_lowmem_zone_present_pages();
>  	list_for_each_entry(bdata, &bdata_list, list)
>  		total_pages += free_all_bootmem_core(bdata);
>  
> diff --git a/mm/nobootmem.c b/mm/nobootmem.c
> index bd82f6b..378d50a 100644
> --- a/mm/nobootmem.c
> +++ b/mm/nobootmem.c
> @@ -126,6 +126,7 @@ unsigned long __init free_low_memory_core_early(int nodeid)
>  	phys_addr_t start, end, size;
>  	u64 i;
>  
> +	reset_lowmem_zone_present_pages();
>  	for_each_free_mem_range(i, MAX_NUMNODES, &start, &end, NULL)
>  		count += __free_memory_core(start, end);
>  
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 07425a7..76d37f0 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -735,6 +735,7 @@ void __meminit __free_pages_bootmem(struct page *page, unsigned int order)
>  {
>  	unsigned int nr_pages = 1 << order;
>  	unsigned int loop;
> +	struct zone *zone;
>  
>  	prefetchw(page);
>  	for (loop = 0; loop < nr_pages; loop++) {
> @@ -748,6 +749,9 @@ void __meminit __free_pages_bootmem(struct page *page, unsigned int order)
>  
>  	set_page_refcounted(page);
>  	__free_pages(page, order);
> +	zone = page_zone(page);
> +	WARN_ON(!(is_normal(zone) || is_dma(zone) || is_dma32(zone)));
> +	zone->present_pages += nr_pages;
>  }
>  
>  #ifdef CONFIG_CMA
> @@ -4547,18 +4551,20 @@ static void __paginginit free_area_init_core(struct pglist_data *pgdat,
>  		 * is used by this zone for memmap. This affects the watermark
>  		 * and per-cpu initialisations
>  		 */
> -		memmap_pages =
> -			PAGE_ALIGN(size * sizeof(struct page)) >> PAGE_SHIFT;
> -		if (realsize >= memmap_pages) {
> -			realsize -= memmap_pages;
> -			if (memmap_pages)
> -				printk(KERN_DEBUG
> -				       "  %s zone: %lu pages used for memmap\n",
> -				       zone_names[j], memmap_pages);
> -		} else
> -			printk(KERN_WARNING
> -				"  %s zone: %lu pages exceeds realsize %lu\n",
> -				zone_names[j], memmap_pages, realsize);
> +		if (j < ZONE_HIGHMEM) {
> +			memmap_pages =
> +				PAGE_ALIGN(size * sizeof(struct page)) >> PAGE_SHIFT;
> +			if (realsize >= memmap_pages) {
> +				realsize -= memmap_pages;
> +				if (memmap_pages)
> +					printk(KERN_DEBUG
> +							"  %s zone: %lu pages used for memmap\n",
> +							zone_names[j], memmap_pages);
> +			} else
> +				printk(KERN_WARNING
> +						"  %s zone: %lu pages exceeds realsize %lu\n",
> +						zone_names[j], memmap_pages, realsize);
> +		}
>  
>  		/* Account for reserved pages */
>  		if (j == 0 && realsize > dma_reserve) {
> @@ -6143,3 +6149,22 @@ void dump_page(struct page *page)
>  	dump_page_flags(page->flags);
>  	mem_cgroup_print_bad_page(page);
>  }
> +
> +/* reset zone->present_pages to 0 for zones below ZONE_HIGHMEM */
> +void reset_lowmem_zone_present_pages_pernode(pg_data_t *pgdat)
> +{
> +	int i;
> +	struct zone *z;
> +	for (i = 0; i < ZONE_HIGHMEM; i++) {
> +		z = pgdat->node_zones + i;
> +		z->present_pages = 0;
> +	}
> +}
> +
> +void reset_lowmem_zone_present_pages(void)
> +{
> +	int nid;
> +
> +	for_each_node_state(nid, N_HIGH_MEMORY)
> +		reset_lowmem_zone_present_pages_pernode(NODE_DATA(nid));
> +}


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