Commit 31932757 authored by Alexander Gordeev's avatar Alexander Gordeev Committed by Vasily Gorbik
Browse files

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: default avatarAlexander Gordeev <agordeev@linux.ibm.com>
Reviewed-by: default avatarHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: default avatarHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: default avatarVasily Gorbik <gor@linux.ibm.com>
parent bb533ec8

arch/s390/mm/pgalloc.c

+56 −34
Original line number Diff line number Diff line
@@ -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;

	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 (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);

		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;



	/*

	 * 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);

		} else {

			crst_table_init(table, _REGION1_ENTRY_EMPTY);

			pgd_populate(mm, (pgd_t *) table, (p4d_t *) pgd);

			mm->pgd = (pgd_t *) table;

	}

	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;

	}

		notify = 1;



	spin_unlock_bh(&mm->page_table_lock);

	}

	if (notify)



	on_each_cpu(__crst_table_upgrade, mm, 0);

	return rc;



	return 0;



err_pgd:

	crst_table_free(mm, p4d);

err_p4d:

	return -ENOMEM;

}



void crst_table_downgrade(struct mm_struct *mm)

CRA Git | Maintained and supported by SUSTech CRA and CCSE