From fe124c95df9e2acf202910b0510300e37afe074b Mon Sep 17 00:00:00 2001 From: Daniel Jordan Date: Tue, 11 Aug 2020 18:32:12 -0700 Subject: [PATCH] x86/mm: use max memory block size on bare metal Some of our servers spend significant time at kernel boot initializing memory block sysfs directories and then creating symlinks between them and the corresponding nodes. The slowness happens because the machines get stuck with the smallest supported memory block size on x86 (128M), which results in 16,288 directories to cover the 2T of installed RAM. The search for each memory block is noticeable even with commit 4fb6eabf1037 ("drivers/base/memory.c: cache memory blocks in xarray to accelerate lookup"). Commit 078eb6aa50dc ("x86/mm/memory_hotplug: determine block size based on the end of boot memory") chooses the block size based on alignment with memory end. That addresses hotplug failures in qemu guests, but for bare metal systems whose memory end isn't aligned to even the smallest size, it leaves them at 128M. Make kernels that aren't running on a hypervisor use the largest supported size (2G) to minimize overhead on big machines. Kernel boot goes 7% faster on the aforementioned servers, shaving off half a second. [daniel.m.jordan@oracle.com: v3] Link: http://lkml.kernel.org/r/20200714205450.945834-1-daniel.m.jordan@oracle.com Signed-off-by: Daniel Jordan Signed-off-by: Andrew Morton Acked-by: David Hildenbrand Cc: Andy Lutomirski Cc: Dave Hansen Cc: David Hildenbrand Cc: Michal Hocko Cc: Pavel Tatashin Cc: Peter Zijlstra Cc: Steven Sistare Cc: Ingo Molnar Cc: "H. Peter Anvin" Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/20200609225451.3542648-1-daniel.m.jordan@oracle.com Signed-off-by: Linus Torvalds --- arch/x86/mm/init_64.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c index 3b246ae40c8f..a4ac13cc3fdc 100644 --- a/arch/x86/mm/init_64.c +++ b/arch/x86/mm/init_64.c @@ -1452,6 +1452,15 @@ static unsigned long probe_memory_block_size(void) goto done; } + /* + * Use max block size to minimize overhead on bare metal, where + * alignment for memory hotplug isn't a concern. + */ + if (!boot_cpu_has(X86_FEATURE_HYPERVISOR)) { + bz = MAX_BLOCK_SIZE; + goto done; + } + /* Find the largest allowed block size that aligns to memory end */ for (bz = MAX_BLOCK_SIZE; bz > MIN_MEMORY_BLOCK_SIZE; bz >>= 1) { if (IS_ALIGNED(boot_mem_end, bz))