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Re: [PATCH 4/6] mm/vmstat: add zone range overlapping check

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  Re: [PATCH 4/6] mm/vmstat: add zone range overlapping check Vlastimil Babka <vbabka@suse.cz> - 2016-03-23 15:50 +0100
    Re: [PATCH 4/6] mm/vmstat: add zone range overlapping check Joonsoo Kim <iamjoonsoo.kim@lge.com> - 2016-03-24 01:10 +0100

#1363469 — Re: [PATCH 4/6] mm/vmstat: add zone range overlapping check

On 03/14/2016 08:31 AM, js1304@gmail.com wrote:
> From: Joonsoo Kim <iamjoonsoo.kim@lge.com>
>
> There is a system that node's pfn are overlapped like as following.
>
> -----pfn-------->
> N0 N1 N2 N0 N1 N2
>
> Therefore, we need to care this overlapping when iterating pfn range.
>
> There are two places in vmstat.c that iterates pfn range and
> they don't consider this overlapping. Add it.
>
> Without this patch, above system could over count pageblock number
> on a zone.
>
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> ---
>   mm/vmstat.c | 7 +++++++
>   1 file changed, 7 insertions(+)
>
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> index 5e43004..0a726e3 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -1010,6 +1010,9 @@ static void pagetypeinfo_showblockcount_print(struct seq_file *m,
>   		if (!memmap_valid_within(pfn, page, zone))
>   			continue;

The above already does this for each page within the block, but it's 
guarded by CONFIG_ARCH_HAS_HOLES_MEMORYMODEL. I guess that's not the 
case of your system, right?

I guess your added check should go above this, though. Also what about 
employing pageblock_pfn_to_page() here and in all other applicable 
places, so it's unified and optimized by zone->contiguous?

>
> +		if (page_zone(page) != zone)
> +			continue;
> +
>   		mtype = get_pageblock_migratetype(page);
>
>   		if (mtype < MIGRATE_TYPES)
> @@ -1076,6 +1079,10 @@ static void pagetypeinfo_showmixedcount_print(struct seq_file *m,
>   				continue;
>
>   			page = pfn_to_page(pfn);
> +
> +			if (page_zone(page) != zone)
> +				continue;
> +
>   			if (PageBuddy(page)) {
>   				pfn += (1UL << page_order(page)) - 1;
>   				continue;
>

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#1363794

On Wed, Mar 23, 2016 at 03:47:46PM +0100, Vlastimil Babka wrote:
> On 03/14/2016 08:31 AM, js1304@gmail.com wrote:
> >From: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> >
> >There is a system that node's pfn are overlapped like as following.
> >
> >-----pfn-------->
> >N0 N1 N2 N0 N1 N2
> >
> >Therefore, we need to care this overlapping when iterating pfn range.
> >
> >There are two places in vmstat.c that iterates pfn range and
> >they don't consider this overlapping. Add it.
> >
> >Without this patch, above system could over count pageblock number
> >on a zone.
> >
> >Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> >---
> >  mm/vmstat.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> >
> >diff --git a/mm/vmstat.c b/mm/vmstat.c
> >index 5e43004..0a726e3 100644
> >--- a/mm/vmstat.c
> >+++ b/mm/vmstat.c
> >@@ -1010,6 +1010,9 @@ static void pagetypeinfo_showblockcount_print(struct seq_file *m,
> >  		if (!memmap_valid_within(pfn, page, zone))
> >  			continue;
> 
> The above already does this for each page within the block, but it's
> guarded by CONFIG_ARCH_HAS_HOLES_MEMORYMODEL. I guess that's not the
> case of your system, right?
> 
> I guess your added check should go above this, though. Also what
> about employing pageblock_pfn_to_page() here and in all other
> applicable places, so it's unified and optimized by
> zone->contiguous?

Comment on memmap_valid_within() in mmzone.h says that page_zone()
linkages could be broken in that system even if pfn_valid() returns
true. So, we cannot do zone check before it.

In fact, I wonder how that system works fine under the situation where
there are many pfn interators which doesn't check
memmap_valid_within(). I guess there may be enough constraint.
Anyway, I think that it is another issue and would be revisited later.

Thanks.

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