linux-kernel - Re: [PATCH] alpha: switch to NO

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Date:   Fri, 29 Jun 2018 11:43:58 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Mike Rapoport <rppt@...ux.vnet.ibm.com>
Cc:     kbuild test robot <lkp@...el.com>, kbuild-all@...org,
        Richard Henderson <rth@...ddle.net>,
        Ivan Kokshaysky <ink@...assic.park.msu.ru>,
        linux-alpha <linux-alpha@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] alpha: switch to NO_BOOTMEM

On Fri 29-06-18 12:24:00, Mike Rapoport wrote:
> On Thu, Jun 28, 2018 at 05:38:29AM +0800, kbuild test robot wrote:
> > Hi Mike,
> > 
> > I love your patch! Yet something to improve:
> > 
> > [auto build test ERROR on linus/master]
> > [also build test ERROR on v4.18-rc2 next-20180627]
> > [if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
> > 
> > url:    https://github.com/0day-ci/linux/commits/Mike-Rapoport/alpha-switch-to-NO_BOOTMEM/20180627-194800
> > config: alpha-allyesconfig (attached as .config)
> > compiler: alpha-linux-gnu-gcc (Debian 7.2.0-11) 7.2.0
> > reproduce:
> >         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
> >         chmod +x ~/bin/make.cross
> >         # save the attached .config to linux build tree
> >         GCC_VERSION=7.2.0 make.cross ARCH=alpha 
> > 
> > All error/warnings (new ones prefixed by >>):
> > 
> >    mm/page_alloc.c: In function 'update_defer_init':
> > >> mm/page_alloc.c:321:14: error: 'PAGES_PER_SECTION' undeclared (first use in this function); did you mean 'USEC_PER_SEC'?
> >          (pfn & (PAGES_PER_SECTION - 1)) == 0) {
> >                  ^~~~~~~~~~~~~~~~~
> >                  USEC_PER_SEC
> 
> The PAGES_PER_SECTION is  defined only for SPARSEMEM with the exception of
> x86-32 defining it for DISCONTIGMEM as well. That said, any architecture
> that can have DISCTONTIGMEM=y && NO_BOOTMEM=y will fail the build with
> DEFERRED_STRUCT_PAGE_INIT enabled.
> 
> The simplest solution seems to make DEFERRED_STRUCT_PAGE_INIT explicitly
> dependent on SPARSEMEM rather than !FLATMEM. The downside is that deferred
> struct page initialization won't be available for x86-32 NUMA setups.

I am really dubious that 32b systems really need DEFERRED_STRUCT_PAGE_INIT.
Regardless of the memory mode. Those systems simply do not have enough
memory to bother. Deferred initialization is targeting much larger
beasts.
-- 
Michal Hocko
SUSE Labs