linux-kernel - Re: [PATCH] mm/zsmalloc: include sparsemem.h for MAX_PHYSMEM

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Date:   Wed, 11 Nov 2020 14:39:46 +0100
From:   Thomas Bogendoerfer <tsbogend@...ha.franken.de>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Mike Rapoport <rppt@...nel.org>, Stefan Agner <stefan@...er.ch>,
        Minchan Kim <minchan@...nel.org>, ngupta@...are.org,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        sjenning@...ux.vnet.ibm.com, gregkh <gregkh@...uxfoundation.org>,
        Arnd Bergmann <arnd@...db.de>, Linux-MM <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm/zsmalloc: include sparsemem.h for MAX_PHYSMEM_BITS

On Wed, Nov 11, 2020 at 11:57:02AM +0100, Arnd Bergmann wrote:
> On Wed, Nov 11, 2020 at 11:26 AM Mike Rapoport <rppt@...nel.org> wrote:
> >
> > On Wed, Nov 11, 2020 at 10:33:29AM +0100, Arnd Bergmann wrote:
> > > On Tue, Nov 10, 2020 at 5:21 PM Mike Rapoport <rppt@...nel.org> wrote:
> > > > On Tue, Nov 10, 2020 at 12:21:11PM +0100, Arnd Bergmann wrote:
> > > > >
> > > > > To be on the safe side, we could provoke a compile-time error
> > > > > when CONFIG_PHYS_ADDR_T_64BIT is set on a 32-bit
> > > > > architecture, but MAX_POSSIBLE_PHYSMEM_BITS is not set.
> > > >
> > > > Maybe compile time warning and a runtime error in zs_init() if 32 bit
> > > > machine has memory above 4G?
> > >
> > > If the fix is as easy as adding a single line in a header, I think a
> > > compile-time
> > > error makes it easier, no need to wait for someone to boot a broken
> > > system before fixing it.
> >
> > Not sure it would be as easy as adding a single line in a header for
> > MIPS with it's diversity.
> 
> I looked up the architecture, and found:
> 
> - The pre-MIPS32r1 cores only support 32-bit addressing
> - octeon selects PHYS_ADDR_T_64BIT but no longer
>   supports 32-bit kernels
> - Alchemy and netlogic (XLR, XLP) have 36-bit addressing
> - CONFIG_XPA implies 40-bit addressing

MIPS32r5 might have up to 60-bit addressing according to the MIPS32 PRA
docuemnt (MD00090). But there is probably no chip, which implements it
so for now 40-bit addressing is correct.

> 
> We should run it by the MIPS maintainers, but I think this patch
> is sufficient:

Do you want me to run it through mips tree or do you need an
Acked-By from me ?

Thomas.

-- 
Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
good idea.                                                [ RFC1925, 2.3 ]