On Fri, Apr 30, 2021 at 11:36:06AM -0300, Leonardo Bras wrote: > Because hypervisors may need to create HPTs without knowing the guest > page size, the smallest used page-size (4k) may be chosen, resulting in > a HPT that is possibly bigger than needed. > > On a guest with bigger page-sizes, the amount of entries for HTP may be > too high, causing the guest to ask for a HPT resize-down on the first > hotplug. > > This becomes a problem when HPT resize-down fails, and causes the > HPT resize to be performed on every LMB added, until HPT size is > compatible to guest memory size, causing a major slowdown. > > So, avoiding HPT resizing-down on hot-add significantly improves memory > hotplug times. > > As an example, hotplugging 256GB on a 129GB guest took 710s without this > patch, and 21s after applied. > > Signed-off-by: Leonardo Bras <leobra...@gmail.com>
Sorry it's taken me so long to look at these
I don't love the extra statefulness that the 'shrinking' parameter
adds, but I can't see an elegant way to avoid it, so:
Reviewed-by: David Gibson <da...@gibson.dropbear.id.au>
> ---
> arch/powerpc/mm/book3s64/hash_utils.c | 36 ++++++++++++++++-----------
> 1 file changed, 21 insertions(+), 15 deletions(-)
>
> diff --git a/arch/powerpc/mm/book3s64/hash_utils.c
> b/arch/powerpc/mm/book3s64/hash_utils.c
> index 581b20a2feaf..608e4ed397a9 100644
> --- a/arch/powerpc/mm/book3s64/hash_utils.c
> +++ b/arch/powerpc/mm/book3s64/hash_utils.c
> @@ -795,7 +795,7 @@ static unsigned long __init htab_get_table_size(void)
> }
>
> #ifdef CONFIG_MEMORY_HOTPLUG
> -static int resize_hpt_for_hotplug(unsigned long new_mem_size)
> +static int resize_hpt_for_hotplug(unsigned long new_mem_size, bool shrinking)
> {
> unsigned target_hpt_shift;
>
> @@ -804,19 +804,25 @@ static int resize_hpt_for_hotplug(unsigned long
> new_mem_size)
>
> target_hpt_shift = htab_shift_for_mem_size(new_mem_size);
>
> - /*
> - * To avoid lots of HPT resizes if memory size is fluctuating
> - * across a boundary, we deliberately have some hysterisis
> - * here: we immediately increase the HPT size if the target
> - * shift exceeds the current shift, but we won't attempt to
> - * reduce unless the target shift is at least 2 below the
> - * current shift
> - */
> - if (target_hpt_shift > ppc64_pft_size ||
> - target_hpt_shift < ppc64_pft_size - 1)
> - return mmu_hash_ops.resize_hpt(target_hpt_shift);
> + if (shrinking) {
>
> - return 0;
> + /*
> + * To avoid lots of HPT resizes if memory size is fluctuating
> + * across a boundary, we deliberately have some hysterisis
> + * here: we immediately increase the HPT size if the target
> + * shift exceeds the current shift, but we won't attempt to
> + * reduce unless the target shift is at least 2 below the
> + * current shift
> + */
> +
> + if (target_hpt_shift >= ppc64_pft_size - 1)
> + return 0;
> +
> + } else if (target_hpt_shift <= ppc64_pft_size) {
> + return 0;
> + }
> +
> + return mmu_hash_ops.resize_hpt(target_hpt_shift);
> }
>
> int hash__create_section_mapping(unsigned long start, unsigned long end,
> @@ -829,7 +835,7 @@ int hash__create_section_mapping(unsigned long start,
> unsigned long end,
> return -1;
> }
>
> - resize_hpt_for_hotplug(memblock_phys_mem_size());
> + resize_hpt_for_hotplug(memblock_phys_mem_size(), false);
>
> rc = htab_bolt_mapping(start, end, __pa(start),
> pgprot_val(prot), mmu_linear_psize,
> @@ -848,7 +854,7 @@ int hash__remove_section_mapping(unsigned long start,
> unsigned long end)
> int rc = htab_remove_mapping(start, end, mmu_linear_psize,
> mmu_kernel_ssize);
>
> - if (resize_hpt_for_hotplug(memblock_phys_mem_size()) == -ENOSPC)
> + if (resize_hpt_for_hotplug(memblock_phys_mem_size(), true) == -ENOSPC)
> pr_warn("Hash collision while resizing HPT\n");
>
> return rc;
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
signature.asc
Description: PGP signature
