linux-kernel - Re: [PATCH v4 1/2] x86/setup: always add the beginning of RAM as memblock.memory

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Date:   Mon, 1 Feb 2021 16:34:29 +0200
From:   Mike Rapoport <rppt@...nel.org>
To:     Baoquan He <bhe@...hat.com>
Cc:     David Hildenbrand <david@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrea Arcangeli <aarcange@...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>, Michal Hocko <mhocko@...nel.org>,
        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 v4 1/2] x86/setup: always add the beginning of RAM as
 memblock.memory

On Mon, Feb 01, 2021 at 07:26:05PM +0800, Baoquan He wrote:
> On 02/01/21 at 10:32am, David Hildenbrand wrote:
> > 
> > 2) In init_zone_unavailable_mem(), similar to round_up(max_pfn,
> > PAGES_PER_SECTION) handling, consider range
> > 	[round_down(min_pfn, PAGES_PER_SECTION), min_pfn - 1]
> > which would handle in the x86-64 case [0..0] and, therefore, initialize PFN
> > 0.
> 
> Sounds reasonable. Maybe we can change to get the real expected lowest
> pfn from find_min_pfn_for_node() by iterating memblock.memory and
> memblock.reserved and comparing.

As I've found out the hard way [1], reserved memory is not necessary present.

There could be a system that instead of reserving memory at 0xfe000000 like
in Guillaume's report, could have it reserved at 0x0 and populated only
from the first gigabyte...
 
[1] https://lore.kernel.org/lkml/127999c4-7d56-0c36-7f88-8e1a5c934cae@collabora.com


-- 
Sincerely yours,
Mike.