• Anton Blanchard's avatar
    powerpc: Increase NODES_SHIFT on 64bit from 4 to 8 · ea55bf29
    Anton Blanchard authored
    Some System p configurations can already have more than 16 nodes so we
    need to increase NODES_SHIFT. I chose 256 to give us some room to grow in the
    future, although we can look at something smaller if the memory bloat is
    considered too much.
    
    Unless we clamp MAX_ACTIVE_REGIONS we end up with 300kB of extra bloat in
    early_node_map in mm/page_alloc.c:
    
    < 6144   early_node_map
    > 307200 early_node_map
    
    due to:
    
        #if MAX_NUMNODES >= 32
          /* If there can be many nodes, allow up to 50 holes per node */
          #define MAX_ACTIVE_REGIONS (MAX_NUMNODES*50)
        #else
          /* By default, allow up to 256 distinct regions */
        #define MAX_ACTIVE_REGIONS 256
    
    Since our memory is mostly contiguous it seems reasonable to keep this
    at 256 for now. I also set 32bit to 32 to save space (is there any chance
    a 32bit system will have more than 32 discontiguous memory ranges?).
    
    Even with that fixed we have a few data structures that grow:
    
    < 896   bootmem_node_data
    > 14336 bootmem_node_data
    
    < 1280  node_devices
    > 20480 node_devices
    
    < 25088 kmalloc_caches
    > 59648 kmalloc_caches
    
    < 1632  hstates
    > 21792 hstates
    Signed-off-by: default avatarAnton Blanchard <anton@samba.org>
    Signed-off-by: default avatarBenjamin Herrenschmidt <benh@kernel.crashing.org>
    ea55bf29
Kconfig 23.5 KB