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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 <agordeev@linux.ibm.com>
Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
This commit is contained in:
Alexander Gordeev 2020-03-08 21:34:49 +01:00 committed by Vasily Gorbik
parent bb533ec8ba
commit 31932757c6
1 changed files with 56 additions and 34 deletions
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90
arch/s390/mm/pgalloc.c
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@ -77,43 +77,65 @@ static void __crst_table_upgrade(void *arg)
int crst_table_upgrade(struct mm_struct *mm, unsigned long end) int crst_table_upgrade(struct mm_struct *mm, unsigned long end)
{ {
unsigned long *table, *pgd; unsigned long *pgd = NULL, *p4d = NULL, *__pgd;
int rc, notify; unsigned long asce_limit = mm->context.asce_limit;
/* upgrade should only happen from 3 to 4, 3 to 5, or 4 to 5 levels */ /* 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); VM_BUG_ON(asce_limit < _REGION2_SIZE);
rc = 0;
notify = 0; if (end <= asce_limit)
while (mm->context.asce_limit < end) { return 0;
table = crst_table_alloc(mm);
if (!table) { if (asce_limit == _REGION2_SIZE) {
rc = -ENOMEM; p4d = crst_table_alloc(mm);
break; if (unlikely(!p4d))
} goto err_p4d;
spin_lock_bh(&mm->page_table_lock); crst_table_init(p4d, _REGION2_ENTRY_EMPTY);
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);
} }
if (notify) if (end > _REGION1_SIZE) {
on_each_cpu(__crst_table_upgrade, mm, 0); pgd = crst_table_alloc(mm);
return rc; 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) void crst_table_downgrade(struct mm_struct *mm)