This is v4 post. V3 can be found here: https://lkml.org/lkml/2018/2/27/928 V1 can be found here: https://www.spinics.net/lists/linux-mm/msg144486.html In sparse_init(), two temporary pointer arrays, usemap_map and map_map are allocated with the size of NR_MEM_SECTIONS. They are used to store each memory section's usemap and mem map if marked as present. In 5-level paging mode, this will cost 512M memory though they will be released at the end of sparse_init(). System with few memory, like kdump kernel which usually only has about 256M, will fail to boot because of allocation failure if CONFIG_X86_5LEVEL=y. In this patchset, optimize the memmap allocation code to only use usemap_map and map_map with the size of nr_present_sections. This makes kdump kernel boot up with normal crashkernel='' setting when CONFIG_X86_5LEVEL=y. Change log: v3->v4: Improve according to Dave's three concerns which are in patch 0004: Rename variable 'idx_present' to 'nr_consumed_maps' which used to index the memmap and usemap of present sections. Add a check if 'nr_consumed_maps' goes beyond nr_present_sections. Add code comment above the final for_each_present_section_nr() to tell why 'nr_consumed_maps' need be increased in each iteration whether the 'ms->section_mem_map' need cleared or out. v2->v3: Change nr_present_sections as __initdata and add code comment according to Andrew's suggestion. Change the local variable 'i' as idx_present which loops over the present sections, and improve the code. These are suggested by Dave and Pankaj. Add a new patch 0003 which adds a new parameter 'data_unit_size' to function alloc_usemap_and_memmap() in which we will update 'data' to make it point at new position. However its type 'void *' can't give us needed info to do that. Need pass the unit size in. So change code in patch 0004 accordingly. This is a code bug fix found when tested the memory deployed on multiple nodes. v1-v2: Split out the nr_present_sections adding as a single patch for easier reviewing. Rewrite patch log according to Dave's suggestion. Fix code bug in patch 0002 reported by test robot. Baoquan He (4): mm/sparse: Add a static variable nr_present_sections mm/sparsemem: Defer the ms->section_mem_map clearing mm/sparse: Add a new parameter 'data_unit_size' for alloc_usemap_and_memmap mm/sparse: Optimize memmap allocation during sparse_init() mm/sparse-vmemmap.c | 6 ++--- mm/sparse.c | 72 +++++++++++++++++++++++++++++++++++++++++------------ 2 files changed, 59 insertions(+), 19 deletions(-) -- 2.13.6
