From: Anton Blanchard Date: Thu, 25 Feb 2010 20:18:46 +0000 (+0000) Subject: powerpc/mm: Bump SECTION_SIZE_BITS from 16MB to 256MB X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=7545ba6f82924d4523f8f8a2baf2e517a750265d;p=linux-beck.git powerpc/mm: Bump SECTION_SIZE_BITS from 16MB to 256MB The current setting for SECTION_SIZE_BITS is quite small compared to everyone else: arch/powerpc/include/asm/sparsemem.h:#define SECTION_SIZE_BITS 24 arch/sparc/include/asm/sparsemem.h:#define SECTION_SIZE_BITS 30 arch/ia64/include/asm/sparsemem.h:#define SECTION_SIZE_BITS (30) arch/s390/include/asm/sparsemem.h:#define SECTION_SIZE_BITS 28 arch/x86/include/asm/sparsemem.h:# define SECTION_SIZE_BITS 27 And it has proven to be an issue during boot on very large machines. If hotplug memory is enabled, drivers/base/memory.c does this: for (i = 0; i < NR_MEM_SECTIONS; i++) { if (!present_section_nr(i)) continue; err = add_memory_block(0, __nr_to_section(i), MEM_ONLINE, 0, BOOT); if (!ret) ret = err; } Which creates a sysfs directory for every 16MB of memory. As a result I'm seeing up to 30 minutes spent here during boot: c000000000248ee0 .__sysfs_add_one+0x28/0x128 c0000000002492a8 .sysfs_add_one+0x38/0x188 c000000000249c88 .create_dir+0x70/0x138 c000000000249d98 .sysfs_create_dir+0x48/0x78 c00000000032bad8 .kobject_add_internal+0x140/0x308 c00000000032beb4 .kobject_init_and_add+0x4c/0x68 c00000000046c2c0 .sysdev_register+0xa0/0x220 c00000000047b1dc .add_memory_block+0x124/0x1e8 c0000000008d1f28 .memory_dev_init+0xf4/0x168 c0000000008d1b64 .driver_init+0x50/0x64 c000000000890378 .do_basic_setup+0x40/0xd4 I assume there are some O(n^2) issues in sysfs as we add all the memory nodes. Bumping SECTION_SIZE_BITS to 256 MB drops the time to about 10 seconds and results in a much smaller /sys. Signed-off-by: Anton Blanchard Signed-off-by: Benjamin Herrenschmidt --- diff --git a/arch/powerpc/include/asm/sparsemem.h b/arch/powerpc/include/asm/sparsemem.h index 54a47ea2c3aa..13fe0a0e5806 100644 --- a/arch/powerpc/include/asm/sparsemem.h +++ b/arch/powerpc/include/asm/sparsemem.h @@ -8,7 +8,7 @@ * MAX_PHYSADDR_BITS 2^N: how much physical address space we have * MAX_PHYSMEM_BITS 2^N: how much memory we can have in that space */ -#define SECTION_SIZE_BITS 24 +#define SECTION_SIZE_BITS 28 #define MAX_PHYSADDR_BITS 44 #define MAX_PHYSMEM_BITS 44