On Tue, Jun 09, 2020 at 06:54:51PM -0400, Daniel Jordan wrote: > 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. > > Signed-off-by: Daniel Jordan <daniel.m.jor...@oracle.com> > Cc: Andrew Morton <a...@linux-foundation.org> > Cc: Andy Lutomirski <l...@kernel.org> > Cc: Dave Hansen <dave.han...@linux.intel.com> > Cc: David Hildenbrand <da...@redhat.com> > Cc: Michal Hocko <mho...@kernel.org> > Cc: Pavel Tatashin <pasha.tatas...@soleen.com> > Cc: Peter Zijlstra <pet...@infradead.org> > Cc: Steven Sistare <steven.sist...@oracle.com> > Cc: linux...@kvack.org > Cc: linux-kernel@vger.kernel.org > ---
Forgot the v1 changes: - Thanks to David for the idea to make this conditional based on virtualization. - Update performance numbers to account for 4fb6eabf1037 (David)