From: David Hildenbrand Date: Mon, 6 Aug 2018 15:54:07 +0000 (+0200) Subject: s390/mm: optimize locking without huge pages in gmap_pmd_op_walk() X-Git-Tag: v4.20-rc1~113^2~108^2~1 X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=af4bf6c3d9b45b62da86d928d3fd2d4ddc8549e6;p=linux.git 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 Reviewed-by: Janosch Frank Message-Id: <20180806155407.15252-1-david@redhat.com> Signed-off-by: Janosch Frank --- 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; }