On Mon, 30 Apr 2018 18:34:32 +1000
Balbir Singh <bsinghar...@gmail.com> wrote:
> This reverts commit 53ecde0b9126ff140abe3aefd7f0ec64d6fa36b0.
>
> The commit above changed the memblock size to 1GiB, which did some
> nice things like create fewer TLB entries for mapping memory at
> the time of hotplug. The downside is that it changes the granularity
> at which memory can be hot-plugged and hot-unplugged. The implication
> is that if we had less than a 1GiB to hot-plug/hot-unplug that
> would not be possible.
>
> The reason we had this fix was to resolve an issue where we did not
> split mappings on hot-unplug, leaving a TLB entry that spanned the
> region that was unplugged. This is now fixed by 4dd5f8a99e79 which
> splits the page table, removing the MMU mappings for the hot-unplugged
> region correctly.
>
> This trade-offs performance as we increase the number of TLB's to
> map 1GiB of memory, mapped in via hot-plug, but gives us the ability
> to handle smaller memory sizes.
Why does powernv have any memory block size override at all now?
>
> Signed-off-by: Balbir Singh <bsinghar...@gmail.com>
> Signed-off-by: Michael Neuling <mi...@neuling.org>
> ---
> arch/powerpc/platforms/powernv/setup.c | 10 +---------
> 1 file changed, 1 insertion(+), 9 deletions(-)
>
> diff --git a/arch/powerpc/platforms/powernv/setup.c
> b/arch/powerpc/platforms/powernv/setup.c
> index ef8c9ce53a61..fa63d3fff14c 100644
> --- a/arch/powerpc/platforms/powernv/setup.c
> +++ b/arch/powerpc/platforms/powernv/setup.c
> @@ -356,15 +356,7 @@ static void pnv_kexec_cpu_down(int crash_shutdown, int
> secondary)
> #ifdef CONFIG_MEMORY_HOTPLUG_SPARSE
> static unsigned long pnv_memory_block_size(void)
> {
> - /*
> - * We map the kernel linear region with 1GB large pages on radix. For
> - * memory hot unplug to work our memory block size must be at least
> - * this size.
> - */
> - if (radix_enabled())
> - return 1UL * 1024 * 1024 * 1024;
> - else
> - return 256UL * 1024 * 1024;
> + return 256UL * 1024 * 1024;
> }
> #endif
>
