From 31932757c6121b394cd4f158b6b8f1cca8ffe871 Mon Sep 17 00:00:00 2001 From: Alexander Gordeev Date: Sun, 8 Mar 2020 21:34:49 +0100 Subject: [PATCH] s390/mm: optimize page table upgrade routine There is a maximum of two new tables allocated on page table upgrade. Because we know that a loop the current implementation is based on could be unrolled with some improvements: * upgrade from 3 to 5 levels happens in one go - without an unnecessary re-take of page_table_lock in-between; * page tables initialization moved out of the atomic code; Signed-off-by: Alexander Gordeev Reviewed-by: Heiko Carstens Signed-off-by: Heiko Carstens Signed-off-by: Vasily Gorbik --- arch/s390/mm/pgalloc.c | 90 ++++++++++++++++++++++++++---------------- 1 file changed, 56 insertions(+), 34 deletions(-) diff --git a/arch/s390/mm/pgalloc.c b/arch/s390/mm/pgalloc.c index 3dd253f81a77..d3be3fe2c55d 100644 --- a/arch/s390/mm/pgalloc.c +++ b/arch/s390/mm/pgalloc.c @@ -77,43 +77,65 @@ static void __crst_table_upgrade(void *arg) int crst_table_upgrade(struct mm_struct *mm, unsigned long end) { - unsigned long *table, *pgd; - int rc, notify; + unsigned long *pgd = NULL, *p4d = NULL, *__pgd; + unsigned long asce_limit = mm->context.asce_limit; /* upgrade should only happen from 3 to 4, 3 to 5, or 4 to 5 levels */ - VM_BUG_ON(mm->context.asce_limit < _REGION2_SIZE); - rc = 0; - notify = 0; - while (mm->context.asce_limit < end) { - table = crst_table_alloc(mm); - if (!table) { - rc = -ENOMEM; - break; - } - spin_lock_bh(&mm->page_table_lock); - pgd = (unsigned long *) mm->pgd; - if (mm->context.asce_limit == _REGION2_SIZE) { - crst_table_init(table, _REGION2_ENTRY_EMPTY); - p4d_populate(mm, (p4d_t *) table, (pud_t *) pgd); - mm->pgd = (pgd_t *) table; - mm->context.asce_limit = _REGION1_SIZE; - mm->context.asce = __pa(mm->pgd) | _ASCE_TABLE_LENGTH | - _ASCE_USER_BITS | _ASCE_TYPE_REGION2; - mm_inc_nr_puds(mm); - } else { - crst_table_init(table, _REGION1_ENTRY_EMPTY); - pgd_populate(mm, (pgd_t *) table, (p4d_t *) pgd); - mm->pgd = (pgd_t *) table; - mm->context.asce_limit = -PAGE_SIZE; - mm->context.asce = __pa(mm->pgd) | _ASCE_TABLE_LENGTH | - _ASCE_USER_BITS | _ASCE_TYPE_REGION1; - } - notify = 1; - spin_unlock_bh(&mm->page_table_lock); + VM_BUG_ON(asce_limit < _REGION2_SIZE); + + if (end <= asce_limit) + return 0; + + if (asce_limit == _REGION2_SIZE) { + p4d = crst_table_alloc(mm); + if (unlikely(!p4d)) + goto err_p4d; + crst_table_init(p4d, _REGION2_ENTRY_EMPTY); } - if (notify) - on_each_cpu(__crst_table_upgrade, mm, 0); - return rc; + if (end > _REGION1_SIZE) { + pgd = crst_table_alloc(mm); + if (unlikely(!pgd)) + goto err_pgd; + crst_table_init(pgd, _REGION1_ENTRY_EMPTY); + } + + spin_lock_bh(&mm->page_table_lock); + + /* + * This routine gets called with mmap_sem lock held and there is + * no reason to optimize for the case of otherwise. However, if + * that would ever change, the below check will let us know. + */ + VM_BUG_ON(asce_limit != mm->context.asce_limit); + + if (p4d) { + __pgd = (unsigned long *) mm->pgd; + p4d_populate(mm, (p4d_t *) p4d, (pud_t *) __pgd); + mm->pgd = (pgd_t *) p4d; + mm->context.asce_limit = _REGION1_SIZE; + mm->context.asce = __pa(mm->pgd) | _ASCE_TABLE_LENGTH | + _ASCE_USER_BITS | _ASCE_TYPE_REGION2; + mm_inc_nr_puds(mm); + } + if (pgd) { + __pgd = (unsigned long *) mm->pgd; + pgd_populate(mm, (pgd_t *) pgd, (p4d_t *) __pgd); + mm->pgd = (pgd_t *) pgd; + mm->context.asce_limit = -PAGE_SIZE; + mm->context.asce = __pa(mm->pgd) | _ASCE_TABLE_LENGTH | + _ASCE_USER_BITS | _ASCE_TYPE_REGION1; + } + + spin_unlock_bh(&mm->page_table_lock); + + on_each_cpu(__crst_table_upgrade, mm, 0); + + return 0; + +err_pgd: + crst_table_free(mm, p4d); +err_p4d: + return -ENOMEM; } void crst_table_downgrade(struct mm_struct *mm)