Re: [PATCH v5 1/1] mm: refactor initialization of struct page for holes in memory layout

From: David Hildenbrand <david@redhat.com>
To: Michal Hocko <mhocko@suse.com>
Cc: "Mike Rapoport" <rppt@kernel.org>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Andrea Arcangeli" <aarcange@redhat.com>,
	"Baoquan He" <bhe@redhat.com>, "Borislav Petkov" <bp@alien8.de>,
	"Chris Wilson" <chris@chris-wilson.co.uk>,
	"H. Peter Anvin" <hpa@zytor.com>,
	"Ingo Molnar" <mingo@redhat.com>,
	"Linus Torvalds" <torvalds@linux-foundation.org>,
	"Łukasz Majczak" <lma@semihalf.com>,
	"Mel Gorman" <mgorman@suse.de>,
	"Mike Rapoport" <rppt@linux.ibm.com>, "Qian Cai" <cai@lca.pw>,
	"Sarvela, Tomi P" <tomi.p.sarvela@intel.com>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Vlastimil Babka" <vbabka@suse.cz>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	stable@vger.kernel.org, x86@kernel.org
Subject: Re: [PATCH v5 1/1] mm: refactor initialization of struct page for holes in memory layout
Date: Fri, 12 Feb 2021 11:16:28 +0100	[thread overview]
Message-ID: <1523f1a6-41be-1fc7-08b9-b777a5b4ef24@redhat.com> (raw)
In-Reply-To: <YCZUOf0jGyWx0IwL@dhcp22.suse.cz>

On 12.02.21 11:11, Michal Hocko wrote:
> On Fri 12-02-21 10:56:19, David Hildenbrand wrote:
>> On 12.02.21 10:55, David Hildenbrand wrote:
>>> On 08.02.21 12:08, Mike Rapoport wrote:
> [...]
>>>> @@ -6519,8 +6581,19 @@ void __init get_pfn_range_for_nid(unsigned int nid,
>>>>     		*end_pfn = max(*end_pfn, this_end_pfn);
>>>>     	}
>>>> -	if (*start_pfn == -1UL)
>>>> +	if (*start_pfn == -1UL) {
>>>>     		*start_pfn = 0;
>>>> +		return;
>>>> +	}
>>>> +
>>>> +#ifdef CONFIG_SPARSEMEM
>>>> +	/*
>>>> +	 * Sections in the memory map may not match actual populated
>>>> +	 * memory, extend the node span to cover the entire section.
>>>> +	 */
>>>> +	*start_pfn = round_down(*start_pfn, PAGES_PER_SECTION);
>>>> +	*end_pfn = round_up(*end_pfn, PAGES_PER_SECTION);
>>>
>>> Does that mean that we might create overlapping zones when one node
>>
>> s/overlapping zones/overlapping nodes/
> 
> I didn't get to review the patch yet. Just wanted to note that we can
> interleave nodes/zone. Or what kind of concern do you have in mind?

I know that we can have it after boot, when hotplugging memory. How 
about during boot?

For example, which node will a PFN then actually be assigned to?

I was just wondering if this might result in issues - if that can 
already happen, then it's just fine I guess.

-- 
Thanks,

David / dhildenb