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)
