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 <[email protected]>
> Cc: Andrew Morton <[email protected]>
> Cc: Andy Lutomirski <[email protected]>
> Cc: Dave Hansen <[email protected]>
> Cc: David Hildenbrand <[email protected]>
> Cc: Michal Hocko <[email protected]>
> Cc: Pavel Tatashin <[email protected]>
> Cc: Peter Zijlstra <[email protected]>
> Cc: Steven Sistare <[email protected]>
> Cc: [email protected]
> Cc: [email protected]
> ---
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)
