On 02/01/18 at 05:49am, Dave Hansen wrote: > On 02/01/2018 02:16 AM, Kirill A. Shutemov wrote: > > On Thu, Feb 01, 2018 at 03:19:56PM +0800, Baoquan He wrote: > >> In sparse_init(), we allocate usemap_map and map_map which are pointer > >> array with the size of NR_MEM_SECTIONS. The memory consumption can be > >> ignorable in 4-level paging mode. While in 5-level paging, this costs > >> much memory, 512M. Kdump kernel even can't boot up with a normal > >> 'crashkernel=' setting. > >> > >> Here add a new variable to record the number of present sections. Let's > >> allocate the usemap_map and map_map with the size of nr_present_sections. > >> We only need to make sure that for the ith present section, usemap_map[i] > >> and map_map[i] store its usemap and mem_map separately. > >> > >> This change can save much memory on most of systems. Anytime, we should > >> avoid to define array or allocate memory with the size of NR_MEM_SECTIONS. > > That's very desirable outcome. But I don't know much about sparsemem. > > ... with the downside being that we can no longer hot-add memory that > was not part of the original, present sections. > > Is that OK? Thanks for looking into this, Dave! I suppose these functions changed here are only called during system bootup, namely in paging_init(). Hot-add memory goes in a different path, __add_section() -> sparse_add_one_section(), different called functions. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
