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

[Shi, Yang]

On 5/23/2016 12:31 AM, Michal Hocko wrote:
> 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

Actually, FLATMEMT depends on !NUMA.

> CONFIG_DEFERRED_STRUCT_PAGE_INIT can we make that explicit please?

Sure, it makes the condition clearer and more readable.

Thanks,
Yang

>