Re: [PATCH 0/6] mm: make movable onlining suck less

[Reza Arbab]

On Tue, Apr 04, 2017 at 10:23:02AM +0200, Michal Hocko wrote:
> OK, so I've been thinkin about that and I believe that page_initialized
> check in get_nid_for_pfn is just bogus. There is nothing to rely on the
> page::lru to be already initialized. So I will go with the following as
> a separate preparatory patch.
>
> I believe the whole code should be revisited and I have put that on my
> ever growing todo list because I suspect that it is more complex than
> necessary. I suspect that memblock do not span more nodes and all this
> is just-in-case code (e.g. the onlining code assumes a single zone aka
> node. But let's do that later.
>
> ---
> From fd2e3b6eca1cf7766527203d23db6aca5957a3f1 Mon Sep 17 00:00:00 2001
> From: Michal Hocko <mhocko@xxxxxxxx>
> Date: Tue, 4 Apr 2017 10:05:06 +0200
> Subject: [PATCH] mm: drop page_initialized check from get_nid_for_pfn
>
> c04fc586c1a4 ("mm: show node to memory section relationship with
> symlinks in sysfs") has added means to export memblock<->node
> association into the sysfs. It has also introduced get_nid_for_pfn
> which is a rather confusing counterpart of pfn_to_nid which checks also
> whether the pfn page is already initialized (page_initialized).  This
> is done by checking page::lru != NULL which doesn't make any sense at
> all. Nothing in this path really relies on the lru list being used or
> initialized. Just remove it
>
> Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
> ---
> drivers/base/node.c | 5 -----
> 1 file changed, 5 deletions(-)
>
> diff --git a/drivers/base/node.c b/drivers/base/node.c
> index 5548f9686016..ee080a35e869 100644
> --- a/drivers/base/node.c
> +++ b/drivers/base/node.c
> @@ -368,8 +368,6 @@ int unregister_cpu_under_node(unsigned int cpu, unsigned int nid)
> }
>
> #ifdef CONFIG_MEMORY_HOTPLUG_SPARSE
> -#define page_initialized(page)  (page->lru.next)
> -
> static int __ref get_nid_for_pfn(unsigned long pfn)
> {
> 	struct page *page;
> @@ -380,9 +378,6 @@ static int __ref get_nid_for_pfn(unsigned long pfn)
> 	if (system_state == SYSTEM_BOOTING)
> 		return early_pfn_to_nid(pfn);
> #endif
> -	page = pfn_to_page(pfn);
> -	if (!page_initialized(page))
> -		return -1;
> 	return pfn_to_nid(pfn);
> }

Verified that /sys/devices/system/node/nodeX/memoryY links are there now.

--
Reza Arbab