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

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Message-ID: <CAHk-=wg-qT41Q1WgPUZPC9UmCi6xquk1KE3_yvxORbmDV3os0g@mail.gmail.com>
Date:   Sun, 31 Jan 2021 13:49:27 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Mike Rapoport <rppt@...nel.org>
Cc:     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>,
        David Hildenbrand <david@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        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 Mailing List <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>, stable <stable@...r.kernel.org>,
        "the arch/x86 maintainers" <x86@...nel.org>
Subject: Re: [PATCH v4 1/2] x86/setup: always add the beginning of RAM as memblock.memory

On Sun, Jan 31, 2021 at 12:04 AM Mike Rapoport <rppt@...nel.org> wrote:
>
> >
> > That's *particularly* true when the very line above it did a
> > "memblock_reserve()" of the exact same range that the memblock_add()
> > "adds".
>
> The most correct thing to do would have been to
>
>         memblock_add(0, end_of_first_memory_bank);
>
> Somewhere at e820__memblock_setup().

You miss my complaint.

Why does the memblock code care about this magical "memblock_add()",
when we just told it that the SAME REGION is reserved by doing a
"memblock_reserve()"?

IOW, I'm not interested in "the correct thing to do would have been
[another memblock_add()]". I'm saying that the memblock code itself is
being confused, and no additional thing should have been required at
all, because we already *did* that memblock_reserve().

See?

Honestly, I'm not seeing it being a good thing to move further towards
memblock code as the primary model for memory initialization, when the
memblock code is so confused.

              Linus