Commit af4bf6c3 authored Aug 06, 2018 by David Hildenbrand Committed by Janosch Frank Oct 01, 2018

s390/mm: optimize locking without huge pages in gmap_pmd_op_walk()



Right now we temporarily take the page table lock in
gmap_pmd_op_walk() even though we know we won't need it (if we can
never have 1mb pages mapped into the gmap).

Let's make this a special case, so gmap_protect_range() and
gmap_sync_dirty_log_pmd() will not take the lock when huge pages are
not allowed.

gmap_protect_range() is called quite frequently for managing shadow
page tables in vSIE environments.

Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
Message-Id: <20180806155407.15252-1-david@redhat.com>
Signed-off-by: Janosch Frank <frankja@linux.ibm.com>

parent 67d49d52

arch/s390/mm/gmap.c

+8 −2

Original line number	Diff line number	Diff line
		@@ -905,10 +905,16 @@ static inline pmd_t gmap_pmd_op_walk(struct gmap gmap, unsigned long gaddr)
		pmd_t *pmdp;

		BUG_ON(gmap_is_shadow(gmap));
		spin_lock(&gmap->guest_table_lock);
		pmdp = (pmd_t *) gmap_table_walk(gmap, gaddr, 1);
		if (!pmdp)
		return NULL;

		if (!pmdp \|\| pmd_none(*pmdp)) {
		/* without huge pages, there is no need to take the table lock */
		if (!gmap->mm->context.allow_gmap_hpage_1m)
		return pmd_none(*pmdp) ? NULL : pmdp;

		spin_lock(&gmap->guest_table_lock);
		if (pmd_none(*pmdp)) {
		spin_unlock(&gmap->guest_table_lock);
		return NULL;
		}

Admin message