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

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Message-ID: <YCZagVNiYz/mRl+2@dhcp22.suse.cz>
Date:   Fri, 12 Feb 2021 11:37:53 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     Mike Rapoport <rppt@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Baoquan He <bhe@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Chris Wilson <chris@...is-wilson.co.uk>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Łukasz Majczak <lma@...ihalf.com>,
        Mel Gorman <mgorman@...e.de>,
        Mike Rapoport <rppt@...ux.ibm.com>, Qian Cai <cai@....pw>,
        "Sarvela, Tomi P" <tomi.p.sarvela@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vlastimil Babka <vbabka@...e.cz>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, stable@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH v5 1/1] mm: refactor initialization of struct page for
 holes in memory layout

On Fri 12-02-21 11:16:28, David Hildenbrand wrote:
> 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?

I have seen systems where NUMA nodes are interleaved.

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

I would have to double check all the details but I do remember there was
a non trivial work to handle those systems.
-- 
Michal Hocko
SUSE Labs