On Fri, Dec 27, 2024 at 01:19:30PM +0530, Anshuman Khandual wrote: > On 12/24/24 19:39, Catalin Marinas wrote: > > On Tue, Dec 24, 2024 at 05:32:06PM +0800, Zhenhua Huang wrote: > >> I have two ideas: > >> 1. Completely disable this PMD mapping optimization since there is no > >> guarantee we must align 128M memory for hotplug .. > > > > I'd be in favour of this, at least if CONFIG_MEMORY_HOTPLUG is enabled. > > I think the only advantage here is that we don't allocate a full 2MB > > block for vmemmap when only plugging in a sub-section. > > Agreed, that will be the right fix for the problem which can be back ported. > We will have to prevent PMD/PUD/CONT mappings for both linear and as well as > vmemmap for all non-boot memory sections, that can be hot-unplugged. I haven't read your diffs below yet but why not allow PMD mappings of the hotplugged memory (not vmemmap)? SUBSECTION_SHIFT is 21, so we can have 2MB blocks in a 4KB page configuration. -- Catalin
