linux-kernel - Re: [PATCH v2 3/3] mm/compaction: speed up pageblock_pfn_to

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Date:	Wed, 10 Feb 2016 14:42:57 +0100
From:	Vlastimil Babka <vbabka@...e.cz>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Joonsoo Kim <js1304@...il.com>, Aaron Lu <aaron.lu@...el.com>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	David Rientjes <rientjes@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux Memory Management List <linux-mm@...ck.org>,
	Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH v2 3/3] mm/compaction: speed up pageblock_pfn_to_page()
 when zone is contiguous

On 02/09/2016 09:53 PM, Andrew Morton wrote:
> On Tue, 9 Feb 2016 18:58:32 +0100 Vlastimil Babka <vbabka@...e.cz> wrote:
> 
>> On 02/05/2016 05:11 PM, Joonsoo Kim wrote:
>>> Yeah, it seems wrong to me. :)
>>> Here goes fix.
>>
>> Doesn't apply for me, even after fixing the most obvious line wraps.
>> Seems like the version in mmotm is still your original patch and
>> Andrew's hotfix?
> 
> Yes, that patch was hopelessly mailer-mangled.  I painstakingly fixed
> it up and generated the incremental:

Thanks a lot. My review of the final patch also involved pain (due to
the cold, not the patch!).

You can take my Acked-by, but I also find the definitions of
set_zone_contiguous/clear_zone_contiguous() "in the header of the
consumer" (hotplug) somewhat unusual. It works, but e.g. mm/internal.h
would be more expected.

Then there's this:

> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -509,6 +509,8 @@ int __ref __add_pages(int nid, struct zone *zone, unsigned long phys_start_pfn,
>  	int start_sec, end_sec;
>  	struct vmem_altmap *altmap;
>  
> +	clear_zone_contiguous(zone);
> +
>  	/* during initialize mem_map, align hot-added range to section */
>  	start_sec = pfn_to_section_nr(phys_start_pfn);
>  	end_sec = pfn_to_section_nr(phys_start_pfn + nr_pages - 1);
> @@ -540,6 +542,8 @@ int __ref __add_pages(int nid, struct zone *zone, unsigned long phys_start_pfn,
>  	}
>  	vmemmap_populate_print_last();
>  
> +	set_zone_contiguous(zone);
> +
>  	return err;
>  }
>  EXPORT_SYMBOL_GPL(__add_pages);

Between the clear and set, __add_pages() might return with -EINVAL,
leaving the flag cleared potentially forever. Not critical, probably
rare, but it should be possible to avoid this by moving the clear below
the altmap check?

Thanks,
Vlastimil