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

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Date:   Wed, 11 Nov 2020 12:26:54 +0200
From:   Mike Rapoport <rppt@...nel.org>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     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 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.

How about adding a runtime detection like Minchan suggested for
!MEMORY_HOTPLUG (e.g. MIPS and ARC) and a compile time error otherwise
(i386, ppc)?

>        Arnd

-- 
Sincerely yours,
Mike.