On Wed, Apr 21, 2021 at 11:41:24AM +0800, Muchun Song wrote: > > Documentation/admin-guide/kernel-parameters.txt already provides an > > explanation on memory_hotplug.memmap_on_memory parameter that states > > that the feature cannot be enabled when using hugetlb-vmemmap > > optimization. > > > > Users can always check whether the feature is enabled via > > /sys/modules/memory_hotplug/parameters/memmap_on_memory. Heh, I realized this is not completely true. Users can check whether the feature is __enabled__ by checking the sys fs, but although it is enabled, it might not be effective. This might be due to a different number of reasons, vmemmap does not fully span a PMD, the size we want to add spans more than a single memory block, etc. That is what "Note that even when enabled, there are a few cases where the feature is not effective." is supposed to mean. Anyway, I did not change my opionion on this. Thanks -- Oscar Salvador SUSE L3
