I plan to fold the following into this patch. --- >From 2cdb8e398eaeddf8b743bddb421dc5d9e49e442d Mon Sep 17 00:00:00 2001 From: Michal Hocko <mho...@suse.com> Date: Thu, 27 Apr 2017 09:53:01 +0200 Subject: [PATCH] fold me "mm: consider zone which is not fully populated to have holes"
- clarify pfn_valid semantic - requested by Joonsoo --- include/linux/mmzone.h | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-) diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index aa8cc03287b0..f8c9453635e5 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -1268,10 +1268,15 @@ unsigned long __init node_memmap_size_bytes(int, unsigned long, unsigned long); #ifdef CONFIG_ARCH_HAS_HOLES_MEMORYMODEL /* * pfn_valid() is meant to be able to tell if a given PFN has valid memmap - * associated with it or not. In FLATMEM, it is expected that holes always - * have valid memmap as long as there is valid PFNs either side of the hole. - * In SPARSEMEM, it is assumed that a valid section has a memmap for the - * entire section. + * associated with it or not. This means that a struct page exists for this + * pfn. The caller cannot assume the page is fully initialized in general. + * Hotplugable pages might not have been onlined yet. pfn_to_online_page() + * will ensure the struct page is fully online and initialized. Special pages + * (e.g. ZONE_DEVICE) are never onlined and should be treated accordingly. + * + * In FLATMEM, it is expected that holes always have valid memmap as long as + * there is valid PFNs either side of the hole. In SPARSEMEM, it is assumed + * that a valid section has a memmap for the entire section. * * However, an ARM, and maybe other embedded architectures in the future * free memmap backing holes to save memory on the assumption the memmap is -- 2.11.0 -- Michal Hocko SUSE Labs
