During memory hotunplug, after each LMB is removed, the HPT may be resized-down if it would map a max of 4 times the current amount of memory. (2 shifts, due to introduced histeresis)
It usually is not an issue, but it can take a lot of time if HPT resizing-down fails. This happens because resize-down failures usually repeat at each LMB removal, until there are no more bolted entries conflict, which can take a while to happen. This can be solved by doing a single HPT resize at the end of memory hotunplug, after all requested entries are removed. To make this happen, it's necessary to temporarily disable all HPT resize-downs before hotunplug, re-enable them after hotunplug ends, and then resize-down HPT to the current memory size. As an example, hotunplugging 256GB from a 385GB guest took 621s without this patch, and 100s after applied. Signed-off-by: Leonardo Bras <leobra...@gmail.com> --- arch/powerpc/include/asm/book3s/64/hash.h | 2 + arch/powerpc/mm/book3s64/hash_utils.c | 45 +++++++++++++++++-- .../platforms/pseries/hotplug-memory.c | 26 +++++++++++ 3 files changed, 70 insertions(+), 3 deletions(-) diff --git a/arch/powerpc/include/asm/book3s/64/hash.h b/arch/powerpc/include/asm/book3s/64/hash.h index fad4af8b8543..6cd66e7e98c9 100644 --- a/arch/powerpc/include/asm/book3s/64/hash.h +++ b/arch/powerpc/include/asm/book3s/64/hash.h @@ -256,6 +256,8 @@ int hash__create_section_mapping(unsigned long start, unsigned long end, int hash__remove_section_mapping(unsigned long start, unsigned long end); void hash_batch_expand_prepare(unsigned long newsize); +void hash_batch_shrink_begin(void); +void hash_batch_shrink_end(void); #endif /* !__ASSEMBLY__ */ #endif /* __KERNEL__ */ diff --git a/arch/powerpc/mm/book3s64/hash_utils.c b/arch/powerpc/mm/book3s64/hash_utils.c index 3fa395b3fe57..73ecd0f61acd 100644 --- a/arch/powerpc/mm/book3s64/hash_utils.c +++ b/arch/powerpc/mm/book3s64/hash_utils.c @@ -795,6 +795,9 @@ static unsigned long __init htab_get_table_size(void) } #ifdef CONFIG_MEMORY_HOTPLUG + +static DEFINE_MUTEX(hpt_resize_down_lock); + static int resize_hpt_for_hotplug(unsigned long new_mem_size, bool shrinking) { unsigned target_hpt_shift; @@ -805,7 +808,7 @@ static int resize_hpt_for_hotplug(unsigned long new_mem_size, bool shrinking) target_hpt_shift = htab_shift_for_mem_size(new_mem_size); if (shrinking) { - + int ret; /* * To avoid lots of HPT resizes if memory size is fluctuating * across a boundary, we deliberately have some hysterisis @@ -818,10 +821,20 @@ static int resize_hpt_for_hotplug(unsigned long new_mem_size, bool shrinking) if (target_hpt_shift >= ppc64_pft_size - 1) return 0; - } else if (target_hpt_shift <= ppc64_pft_size) { - return 0; + /* When batch removing entries, only resizes HPT at the end. */ + + if (!mutex_trylock(&hpt_resize_down_lock)) + return 0; + + ret = mmu_hash_ops.resize_hpt(target_hpt_shift); + + mutex_unlock(&hpt_resize_down_lock); + return ret; } + if (target_hpt_shift <= ppc64_pft_size) + return 0; + return mmu_hash_ops.resize_hpt(target_hpt_shift); } @@ -879,6 +892,32 @@ void hash_batch_expand_prepare(unsigned long newsize) break; } } + +void hash_batch_shrink_begin(void) +{ + /* Disable HPT resize-down during hot-unplug */ + mutex_lock(&hpt_resize_down_lock); +} + +void hash_batch_shrink_end(void) +{ + const u64 starting_size = ppc64_pft_size; + unsigned long newsize; + + newsize = memblock_phys_mem_size(); + /* Resize to smallest SHIFT possible */ + while (resize_hpt_for_hotplug(newsize, true) == -ENOSPC) { + newsize *= 2; + pr_warn("Hash collision while resizing HPT\n"); + + /* Do not try to resize to the starting size, or bigger value */ + if (htab_shift_for_mem_size(newsize) >= starting_size) + break; + } + + /* Re-enables HPT resize-down after hot-unplug */ + mutex_unlock(&hpt_resize_down_lock); +} #endif /* CONFIG_MEMORY_HOTPLUG */ static void __init hash_init_partition_table(phys_addr_t hash_table, diff --git a/arch/powerpc/platforms/pseries/hotplug-memory.c b/arch/powerpc/platforms/pseries/hotplug-memory.c index 48b2cfe4ce69..44bc50d72353 100644 --- a/arch/powerpc/platforms/pseries/hotplug-memory.c +++ b/arch/powerpc/platforms/pseries/hotplug-memory.c @@ -426,6 +426,9 @@ static int dlpar_memory_remove_by_count(u32 lmbs_to_remove) return -EINVAL; } + if (!radix_enabled()) + hash_batch_shrink_begin(); + for_each_drmem_lmb(lmb) { rc = dlpar_remove_lmb(lmb); if (rc) @@ -471,6 +474,9 @@ static int dlpar_memory_remove_by_count(u32 lmbs_to_remove) rc = 0; } + if (!radix_enabled()) + hash_batch_shrink_end(); + return rc; } @@ -533,6 +539,9 @@ static int dlpar_memory_remove_by_ic(u32 lmbs_to_remove, u32 drc_index) if (lmbs_available < lmbs_to_remove) return -EINVAL; + if (!radix_enabled()) + hash_batch_shrink_begin(); + for_each_drmem_lmb_in_range(lmb, start_lmb, end_lmb) { if (!(lmb->flags & DRCONF_MEM_ASSIGNED)) continue; @@ -573,6 +582,9 @@ static int dlpar_memory_remove_by_ic(u32 lmbs_to_remove, u32 drc_index) } } + if (!radix_enabled()) + hash_batch_shrink_end(); + return rc; } @@ -703,6 +715,9 @@ static int dlpar_memory_add_by_count(u32 lmbs_to_add) if (lmbs_added != lmbs_to_add) { pr_err("Memory hot-add failed, removing any added LMBs\n"); + if (!radix_enabled()) + hash_batch_shrink_begin(); + for_each_drmem_lmb(lmb) { if (!drmem_lmb_reserved(lmb)) continue; @@ -716,6 +731,10 @@ static int dlpar_memory_add_by_count(u32 lmbs_to_add) drmem_remove_lmb_reservation(lmb); } + + if (!radix_enabled()) + hash_batch_shrink_end(); + rc = -EINVAL; } else { for_each_drmem_lmb(lmb) { @@ -817,6 +836,9 @@ static int dlpar_memory_add_by_ic(u32 lmbs_to_add, u32 drc_index) if (rc) { pr_err("Memory indexed-count-add failed, removing any added LMBs\n"); + if (!radix_enabled()) + hash_batch_shrink_begin(); + for_each_drmem_lmb_in_range(lmb, start_lmb, end_lmb) { if (!drmem_lmb_reserved(lmb)) continue; @@ -830,6 +852,10 @@ static int dlpar_memory_add_by_ic(u32 lmbs_to_add, u32 drc_index) drmem_remove_lmb_reservation(lmb); } + + if (!radix_enabled()) + hash_batch_shrink_end(); + rc = -EINVAL; } else { for_each_drmem_lmb_in_range(lmb, start_lmb, end_lmb) { -- 2.30.2