Re: why do we still need bootmem allocator?

[Mike Rapoport]

Hi,

On Mon, Jun 25, 2018 at 10:09:41AM -0600, Rob Herring wrote:
> On Mon, Jun 25, 2018 at 8:08 AM Michal Hocko <mhocko@xxxxxxxxxx> wrote:
> >
> > Hi,
> > I am wondering why do we still keep mm/bootmem.c when most architectures
> > already moved to nobootmem. Is there any fundamental reason why others
> > cannot or this is just a matter of work?
> 
> Just because no one has done the work. I did a couple of arches
> recently (sh, microblaze, and h8300) mainly because I broke them with
> some DT changes.

I've tried running the current upstream on h8300 gdb simulator and it
failed:

[    0.000000] BUG: Bad page state in process swapper  pfn:00004
[    0.000000] page:007ed080 count:0 mapcount:-128 mapping:00000000
index:0x0
[    0.000000] flags: 0x0()
[    0.000000] raw: 00000000 0040bdac 0040bdac 00000000 00000000 00000002
ffffff7f 00000000
[    0.000000] page dumped because: nonzero mapcount
---Type <return> to continue, or q <return> to quit---
[    0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 4.18.0-rc2+ #50
[    0.000000] Stack from 00401f2c:
[    0.000000]   00401f2c 001116cb 007ed080 00401f40 000e20e6 00401f54
0004df14 00000000
[    0.000000]   007ed080 007ed000 00401f5c 0004df8c 00401f90 0004e982
00000044 00401fd1
[    0.000000]   007ed000 007ed000 00000000 00000004 00000008 00000000
00000003 00000011
[    0.000000] 
[    0.000000] Call Trace:
[    0.000000]         [<000e20e6>] [<0004df14>] [<0004df8c>] [<0004e982>]
[    0.000000]         [<00051a28>] [<00001000>] [<00000100>]
[    0.000000] Disabling lock debugging due to kernel taint

With v4.13 I was able to get to "no valid init found".

I had a quick look at h8300 memory initialization and it seems it has
starting pfn set to 0 while fdt defines memory start at 4M.
 
> > Btw. what really needs to be
> > done? Btw. is there any documentation telling us what needs to be done
> > in that regards?
> 
> No. The commits converting the arches are the only documentation. It's
> a bit more complicated for platforms that have NUMA support.
> 
> Rob
> 

-- 
Sincerely yours,
Mike.