linux-kernel - Re: [PATCH v4 0/4] MIPS: Modify mem= and memmap= parameter

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Date:   Tue, 1 Mar 2022 16:31:46 +0200
From:   Mike Rapoport <rppt@...nel.org>
To:     Tiezhu Yang <yangtiezhu@...ngson.cn>
Cc:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Xuefeng Li <lixuefeng@...ngson.cn>, linux-mips@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 0/4] MIPS: Modify mem= and memmap= parameter

On Tue, Mar 01, 2022 at 07:51:23PM +0800, Tiezhu Yang wrote:
> 
> 
> On 03/01/2022 05:55 PM, Mike Rapoport wrote:
> > Hi,
> > 
> > On Tue, Mar 01, 2022 at 12:28:57PM +0800, Tiezhu Yang wrote:
> > > In the current code, the kernel command-line parameter mem= and memmap=
> > > can not work well on MIPS, this patchset refactors the related code to
> > > fix them.
> > > 
> > > For kdump on MIPS, if the users want to limit the memory region for the
> > > capture kernel to avoid corrupting the memory image of the panic kernel,
> > > use the parameter memmap=limit@...e is the proper way, I will submit a
> > > patch to use memmap=limit@...e for kexec-tools after this patchset is
> > > applied.
> > 
> > Sorry, apparently I misread the prevoius version.
> > What's wrong with the current implementation of mem=limit@...e for the
> > kdump case?
> 
> In the current code, without this patchset, kernel boot hangs when add
> mem=3G, mem=3G@64M or memmap=3G@64M to the command-line, it means that
> the parameter mem= and memmap= have bug on mips.

I can see how mem=3G may be wrong when the memory does not start at 0, but
it seems to do the right thing of mem=3G@.... 

Do you see system hangs with mem=3G@...?

Do you have the logs before the hang?

As for memmap= option, it does not specify the memory map but rather alters
the memory map passed by the firmware. Particularity in MIPS implementation
it allows to add a single range of available or reserved memory.

AFAIU, for the kdump use-case mem=X@Y should suffice.

> Thanks,
> Tiezhu
> 
> > 
> > > v4: Fix some build warnings reported by kernel test robot
> > > 
> > > v3: Modify patch #3 to maintain compatibility for memmap=limit{$,#,!}base,
> > >     commented by Mike Rapoport, thank you
> > > 
> > > v2: Add some new patches to support memmap=limit@...e
> > > 
> > > Tiezhu Yang (4):
> > >   MIPS: Refactor early_parse_mem() to fix mem= parameter
> > >   memblock: Introduce memblock_mem_range_remove_map()
> > >   MIPS: Refactor early_parse_memmap() to fix memmap= parameter
> > >   MIPS: Remove not used variable usermem
> > > 
> > >  arch/mips/kernel/setup.c | 69 ++++++++++++++++++++++--------------------------
> > >  include/linux/memblock.h |  1 +
> > >  mm/memblock.c            |  9 +++++--
> > >  3 files changed, 40 insertions(+), 39 deletions(-)
> > > 
> > > --
> > > 2.1.0
> > > 
> > 
> 

-- 
Sincerely yours,
Mike.