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

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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>
This commit is contained in:
David Hildenbrand 2018-08-06 17:54:07 +02:00 committed by Janosch Frank
parent 67d49d52ae
commit af4bf6c3d9
1 changed files with 8 additions and 2 deletions
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10
arch/s390/mm/gmap.c
View file

@ -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;
}