linux-kernel - Re: why do we still need bootmem allocator?

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Message-Id: <20180627160206.GB19182@rapoport-lnx>
Date:   Wed, 27 Jun 2018 19:02:07 +0300
From:   Mike Rapoport <rppt@...ux.vnet.ibm.com>
To:     Rob Herring <robh@...nel.org>
Cc:     mhocko@...nel.org, linux-mm@...ck.org,
        Johannes Weiner <hannes@...xchg.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "open list:GENERIC INCLUDE/ASM HEADER FILES" 
        <linux-arch@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: why do we still need bootmem allocator?

On Wed, Jun 27, 2018 at 07:33:55AM -0600, Rob Herring wrote:
> On Wed, Jun 27, 2018 at 5:27 AM Mike Rapoport <rppt@...ux.vnet.ibm.com> wrote:
> >
> > 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@...nel.org> 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:
> 
> It seems my patch[1] is still not applied. The maintainer said he applied it.

I've applied it manually. Without it unflatten_and_copy_device_tree() fails
to allocate memory. It indeed can be fixed with moving bootmem_init()
before, as you've noted in the commit message.

I'll try to dig deeper into it.
 
> > [    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.
> 
> Perhaps there's another issue.
> 
> Rob
> 
> [1] https://patchwork.kernel.org/patch/10290317/
> 

-- 
Sincerely yours,
Mike.