On Tue 04-04-17 09:34:12, Michal Hocko wrote:
> On Tue 04-04-17 09:23:29, Michal Hocko wrote:
> > [Let's add Gary who as introduced this code c04fc586c1a48]
>
> OK, so Gary's email doesn't exist anymore. Does anybody can comment on
> this? I suspect this code is just-in-case... Mel?
>
> > On Mon 03-04-17 15:42:13, Reza Arbab wrote:
> [...]
> > > Almost there. I'm seeing the memory in the correct node now, but the
> > > /sys/devices/system/node/nodeX/memoryY links are not being created.
> > >
> > > I think it's tripping up here, in register_mem_sect_under_node():
> > >
> > > page_nid = get_nid_for_pfn(pfn);
> > > if (page_nid < 0)
> > > continue;
> >
> > Huh, this code is confusing. How can we have a memblock spanning more
> > nodes? If not then the loop over all sections in the memblock seem
> > pointless as well. Also why do we require page_initialized() in
> > get_nid_for_pfn? The changelog doesn't explain that and there are no
> > comments that would help either.
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);
}
--
2.11.0
--
Michal Hocko
SUSE Labs
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