lkml.org 
[lkml]   [2018]   [Aug]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH] s390x/mm: avoid taking the table lock in gmap_pmd_op_walk()
Date
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).

So let's special case this, so
gmap_protect_range()/gmap_sync_dirty_log_pmd() will not take the lock in
case 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>
---
arch/s390/mm/gmap.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
index bb44990c8212..d4fa0a4514e0 100644
--- a/arch/s390/mm/gmap.c
+++ b/arch/s390/mm/gmap.c
@@ -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;
}
--
2.17.1
\
 
 \ /
  Last update: 2018-08-06 17:54    [W:0.154 / U:0.976 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site