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

[Mike Rapoport <rppt@kernel.org>]

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@base is the proper way, I will submit a
> > > patch to use memmap=limit@base 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@base 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@64M. 

Do you see system hangs with mem=3G@64M?

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@base
> > > 
> > > 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.