From: Mike Rapoport <rppt@kernel.org>
To: "Maciej W. Rozycki" <macro@orcam.me.uk>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
Tiezhu Yang <yangtiezhu@loongson.cn>,
Andrew Morton <akpm@linux-foundation.org>,
Xuefeng Li <lixuefeng@loongson.cn>,
linux-mips@vger.kernel.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4 1/4] MIPS: Refactor early_parse_mem() to fix mem= parameter
Date: Sat, 5 Mar 2022 15:13:54 +0200 [thread overview]
Message-ID: <YiNiEqC294xQ6PXD@kernel.org> (raw)
In-Reply-To: <alpine.DEB.2.21.2203041634040.47558@angie.orcam.me.uk>
On Fri, Mar 04, 2022 at 05:11:44PM +0000, Maciej W. Rozycki wrote:
> On Fri, 4 Mar 2022, Thomas Bogendoerfer wrote:
>
> > > > With this patch, when add "mem=3G" to the command-line, the
> > > > kernel boots successfully, we can see the following messages:
> > >
> > > unfortunately this patch would break platforms without memory detection,
> > > which simply use mem=32M for memory configuration. Not sure how many
> > > rely on this mechanism. If we can make sure nobody uses it, I'm fine
> > > with your patch.
> >
> > maybe we could add a CONFIG option, which will be selected by
> > platforms, which don't need/want this usermem thing.
>
> FWIW I don't understand what the issue is here beyond that we have a bug
> that causes a system to hang when "mem=3G" is passed on the kernel command
> line. That is assuming that system does have contiguous RAM available for
> the kernel to use from address 0 up to 3GiB; otherwise it's a user error
> to tell the kernel it has that memory available (I did get bitten by that
> myself too): garbage in, garbage out.
This is exactly the case here because the system does not have contiguous
RAM:
[ 0.000000] Early memory node ranges
[ 0.000000] node 0: [mem 0x0000000004000000-0x000000000effffff]
[ 0.000000] node 0: [mem 0x0000000090200000-0x00000000ffffffff]
[ 0.000000] node 0: [mem 0x0000000120000000-0x00000001653fffff]
(from patch 3/4 in this series)
I don't see what "bug" this patch is trying to fix. Is indeed possible to
make MIPS' mem= behave like it does not arm64 and ppc, but that would break
systems that use current semantics and I recall seeing some of OpenWRT
machines using mem= to override memory map supplied by firmware.
> Maciej
--
Sincerely yours,
Mike.
next prev parent reply other threads:[~2022-03-05 13:14 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-01 4:28 [PATCH v4 0/4] MIPS: Modify mem= and memmap= parameter Tiezhu Yang
2022-03-01 4:28 ` [PATCH v4 1/4] MIPS: Refactor early_parse_mem() to fix mem= parameter Tiezhu Yang
2022-03-04 15:10 ` Thomas Bogendoerfer
2022-03-04 15:35 ` Thomas Bogendoerfer
2022-03-04 17:11 ` Maciej W. Rozycki
2022-03-05 13:13 ` Mike Rapoport [this message]
2022-03-07 16:29 ` Thomas Bogendoerfer
2022-03-07 22:07 ` Mike Rapoport
2022-03-07 23:09 ` Maciej W. Rozycki
2022-03-01 4:28 ` [PATCH v4 2/4] memblock: Introduce memblock_mem_range_remove_map() Tiezhu Yang
2022-03-01 4:29 ` [PATCH v4 3/4] MIPS: Refactor early_parse_memmap() to fix memmap= parameter Tiezhu Yang
2022-03-01 4:29 ` [PATCH v4 4/4] MIPS: Remove not used variable usermem Tiezhu Yang
2022-03-01 9:55 ` [PATCH v4 0/4] MIPS: Modify mem= and memmap= parameter Mike Rapoport
2022-03-01 11:51 ` Tiezhu Yang
2022-03-01 14:31 ` Mike Rapoport
2022-03-02 1:50 ` Tiezhu Yang
2022-03-02 8:03 ` Mike Rapoport
2022-03-02 9:28 ` Tiezhu Yang
2022-03-02 12:50 ` Mike Rapoport
2022-03-04 17:05 ` Maciej W. Rozycki
2022-03-05 6:19 ` Tiezhu Yang
2022-03-05 13:26 ` Mike Rapoport
2022-03-05 19:21 ` Maciej W. Rozycki
2022-03-05 20:09 ` Mike Rapoport
2022-03-06 1:22 ` Maciej W. Rozycki
2022-03-05 20:53 ` Maciej W. Rozycki
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