Re: [PATCH] mm/hotplug: fix an imbalance with DEBUG_PAGEALLOC

[Michal Hocko]

On Mon 25-02-19 14:17:10, Qian Cai wrote:
> When onlining memory pages, it calls kernel_unmap_linear_page(),
> However, it does not call kernel_map_linear_page() while offlining
> memory pages. As the result, it triggers a panic below while onlining on
> ppc64le as it checks if the pages are mapped before unmapping,
> Therefore, let it call kernel_map_linear_page() when setting all pages
> as reserved.

This really begs for much more explanation. All the pages should be
unmapped as they get freed AFAIR. So why do we need a special handing
here when this path only offlines free pages?

-- 
Michal Hocko
SUSE Labs