Re: [PATCH v1] drivers/base/node.c: get rid of get_nid_for_pfn()

[David Hildenbrand <david@redhat.com>]

On 28.11.19 12:50, Michal Hocko wrote:
> On Thu 28-11-19 12:23:08, David Hildenbrand wrote:
> [...]
>> >From fc13fd540a1702592e389e821f6266098e41e2bd Mon Sep 17 00:00:00 2001
>> From: David Hildenbrand <david@redhat.com>
>> Date: Wed, 27 Nov 2019 16:18:42 +0100
>> Subject: [PATCH] drivers/base/node.c: optimize get_nid_for_pfn()
>>
>> Since commit d84f2f5a7552 ("drivers/base/node.c: simplify
>> unregister_memory_block_under_nodes()") we only have a single user of
>> get_nid_for_pfn(). The remaining user calls this function when booting -
>> where all added memory is online.
>>
>> Make it clearer that this function should only be used during boot (
>> e.g., calling it on offline memory would be bad) by renaming the
>> function to something meaningful, optimize out the ifdef and the additional
>> system_state check, and add a comment why CONFIG_DEFERRED_STRUCT_PAGE_INIT
>> handling is in place at all.
>>
>> Also, optimize the call site. There is no need to check against
>> page_nid < 0 - it will never match the nid (nid >= 0).
>>
>> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>> Cc: "Rafael J. Wysocki" <rafael@kernel.org>
>> Cc: Michal Hocko <mhocko@kernel.org>
>> Cc: Oscar Salvador <osalvador@suse.de>
>> Cc: Andrew Morton <akpm@linux-foundation.org>
>> Signed-off-by: David Hildenbrand <david@redhat.com>
> 
> Yes this looks much better! I am not sure this will pass all weird
> config combinations because IS_ENABLED will not hide early_pfn_to_nid
> from the early compiler stages so it might complain. But if this passes
> 0day compile scrutiny then this is much much better. If not then we just
> have to use ifdef which is a minor thing.

The compiler should optimize out

if (0)
	code

and therefore never link to early_pfn_to_nid.

Will give it a try, though - thanks!

> 
> Acked-by: Michal Hocko <mhocko@suse.com>
> 
> Thanks!


-- 
Thanks,

David / dhildenb