linux-kernel - Re: [v2 PATCH] mm: move page_ext_init after all struct pages are initialized

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Date:	Mon, 23 May 2016 09:31:58 +0200
From:	Michal Hocko <mhocko@...nel.org>
To:	"Shi, Yang" <yang.shi@...aro.org>
Cc:	akpm@...ux-foundation.org, iamjoonsoo.kim@....com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linaro-kernel@...ts.linaro.org
Subject: Re: [v2 PATCH] mm: move page_ext_init after all struct pages are
 initialized

On Fri 20-05-16 08:41:09, Shi, Yang wrote:
> On 5/20/2016 6:16 AM, Michal Hocko wrote:
> > On Thu 19-05-16 15:13:26, Yang Shi wrote:
> > [...]
> > > diff --git a/init/main.c b/init/main.c
> > > index b3c6e36..2075faf 100644
> > > --- a/init/main.c
> > > +++ b/init/main.c
> > > @@ -606,7 +606,6 @@ asmlinkage __visible void __init start_kernel(void)
> > >  		initrd_start = 0;
> > >  	}
> > >  #endif
> > > -	page_ext_init();
> > >  	debug_objects_mem_init();
> > >  	kmemleak_init();
> > >  	setup_per_cpu_pageset();
> > > @@ -1004,6 +1003,8 @@ static noinline void __init kernel_init_freeable(void)
> > >  	sched_init_smp();
> > > 
> > >  	page_alloc_init_late();
> > > +	/* Initialize page ext after all struct pages are initializaed */
> > > +	page_ext_init();
> > > 
> > >  	do_basic_setup();
> > 
> > I might be missing something but don't we have the same problem with
> > CONFIG_FLATMEM? page_ext_init_flatmem is called way earlier. Or
> > CONFIG_DEFERRED_STRUCT_PAGE_INIT is never enabled for CONFIG_FLATMEM?
> 
> Yes, CONFIG_DEFERRED_STRUCT_PAGE_INIT depends on MEMORY_HOTPLUG which
> depends on SPARSEMEM. So, this config is not valid for FLATMEM at all.

Well
config MEMORY_HOTPLUG
        bool "Allow for memory hot-add"
	depends on SPARSEMEM || X86_64_ACPI_NUMA
	depends on ARCH_ENABLE_MEMORY_HOTPLUG

I wasn't really sure about X86_64_ACPI_NUMA dependency branch which
depends on X86_64 && NUMA && ACPI && PCI and that didn't sound like
SPARSEMEM only. If the FLATMEM shouldn't exist with
CONFIG_DEFERRED_STRUCT_PAGE_INIT can we make that explicit please?
-- 
Michal Hocko
SUSE Labs