On Tue 26-02-19 09:16:30, Qian Cai wrote: > > > On 2/26/19 7:35 AM, Michal Hocko wrote: > > 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? > > > > It sounds like this is exact the point to explain the imbalance. When offlining, > every page has already been unmapped and marked reserved. When onlining, it > tries to free those reserved pages via __online_page_free(). Since those pages > are order 0, it goes free_unref_page() which in-turn call > kernel_unmap_linear_page() again without been mapped first. How is this any different from an initial page being freed to the allocator during the boot? -- Michal Hocko SUSE Labs
