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Date:   Thu, 23 Nov 2023 13:12:50 +0300
From:   Serge Semin <fancer.lancer@gmail.com>
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        Mike Rapoport <rppt@kernel.org>,
        Matthew Wilcox <willy@infradead.org>,
        Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>,
        Arnd Bergmann <arnd@arndb.de>,
        Aleksandar Rikalo <aleksandar.rikalo@syrmia.com>,
        Aleksandar Rikalo <arikalo@gmail.com>,
        Dragan Mladjenovic <dragan.mladjenovic@syrmia.com>,
        Chao-ying Fu <cfu@wavecomp.com>,
        Jiaxun Yang <jiaxun.yang@flygoat.com>,
        Yinglu Yang <yangyinglu@loongson.cn>,
        Tiezhu Yang <yangtiezhu@loongson.cn>,
        Marc Zyngier <maz@kernel.org>, linux-mips@vger.kernel.org,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 0/7] MIPS: mm: Fix some memory-related issues
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References: <20231122182419.30633-1-fancer.lancer@gmail.com>
 <20231122102900.68216218f77b61e342f37627@linux-foundation.org>
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On Wed, Nov 22, 2023 at 10:29:00AM -0800, Andrew Morton wrote:
> On Wed, 22 Nov 2023 21:23:58 +0300 Serge Semin <fancer.lancer@gmail.com> wrote:
> 
> > Just recently I've rebased my MIPS32-related work from kernel 6.5-rc4 onto
> > the latest kernel 6.7-rc1 and immediately got into a bootup-time
> > mm-related bug (see patches 3-5 in this series). After fixing it I decided
> > it was time to submit for review the generic MIPS code fixes which I have
> > been collecting in my local repo for the last year. I was going to submit
> > them a bit later after I finished working on a patchset with my SoC
> > arch-specific changes, but since it was getting bigger and bigger, it
> > turned to be reasonable to spill out the generic part of series right away
> > especially seeing it might get to be useful in the most recent kernel.
> 

> It would have been better to separate out the two tiny unrelated MM
> patches from this series. 

One of them isn't completely unrelated to the series content. The
biggest problem I fixed in the patch
[PATCH 3/7] mips: Fix max_mapnr being uninitialized on early stages
Link: https://lore.kernel.org/linux-mips/20231122182419.30633-4-fancer.lancer@gmail.com/
of this series. I was sure that it was a correct fix at least for
having the pfn_valid() method working incorrectly, but I had doubts
whether the memory mapped IO pages were supposed to be left
uninitialized by the arch code relying on the init_unavailable_range()
doing that especially seeing it was printing a warning about having
unavailable ranges. If it turned out to be incorrect I would have
needed to drop the patch
[PATCH 5/7] mm/mm_init.c: Extend init unavailable range doc info
Link: https://lore.kernel.org/linux-mips/20231122182419.30633-6-fancer.lancer@gmail.com/
and fix that problem too in the framework of the MIPS arch.

My alternative assumption regarding that problem was that the
arch-code should have used memblock_reserve() method for the IO
ranges, so then the calls-chain:
mem_init()
+-> memblock_free_all()
    +-> free_low_memory_core_early()
        +-> memmap_init_reserved_pages()
            +-> memmap_init_reserved_pages(v)
                +-> for_each_reserved_mem_region(region)
                    +-> reserve_bootmem_region(start, end, nid);
would have properly initialized the IO-pages reserved earlier by means
of the memblock_reserve() method. But it turned out that
reserve_bootmem_region() was available only when
CONFIG_DEFERRED_STRUCT_PAGE_INIT was enabled which didn't seem to be
widespreadly utilized in the arch code. Not finding a better option I
decided to stick to the solution relying on the
init_unavailable_range() method doing the trick and just fix the
method kdoc. Seeing you accepted the patch
[PATCH 5/7] mm/mm_init.c: Extend init unavailable range doc info
it was a correct decision.

> I'll steal them - if they later turn up via
> the MIPS tree then that's OK.

Ok. Thanks for picking them up. I'll drop those two patches from the
series on v2.

-Serge(y)