[PATCH 04/14] s390/sclp_ctl: Replace get_zeroed_page() with kzalloc()

["Mike Rapoport (Microsoft)" <rppt@kernel.org>]

sclp_ctl_ioctl_sccb() allocates the SCCB that carries a user supplied
SCLP command.

This buffer can be allocated with kmalloc() as there's nothing special
about it to go directly to the page allocator.

kmalloc() provides a better API that does not require ugly casts and
kfree() does not need to know the size of the freed object.

Performance difference between kmalloc() and __get_free_pages() is not
measurable as both allocators take an object/page from a per-CPU list for
fast path allocations.

For the slow path the performance is anyway determined by the amount of
reclaim involved rather than by what allocator is used.

Replace use of get_zeroed_page() with kzalloc() and free_page() with
kfree().

Link: https://lore.kernel.org/all/635405e4-9423-4a25-a6e7-e03c8ea0bcbe@redhat.com
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
---
 drivers/s390/char/sclp_ctl.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/s390/char/sclp_ctl.c b/drivers/s390/char/sclp_ctl.c
index e23a97359286b..84aefff3be98f 100644
--- a/drivers/s390/char/sclp_ctl.c
+++ b/drivers/s390/char/sclp_ctl.c
@@ -8,6 +8,7 @@
  */
 
 #include <linux/uaccess.h>
+#include <linux/slab.h>
 #include <linux/miscdevice.h>
 #include <linux/gfp.h>
 #include <linux/init.h>
@@ -59,7 +60,7 @@ static int sclp_ctl_ioctl_sccb(void __user *user_area)
 		return -EFAULT;
 	if (!sclp_ctl_cmdw_supported(ctl_sccb.cmdw))
 		return -EOPNOTSUPP;
-	sccb = (void *) get_zeroed_page(GFP_KERNEL | GFP_DMA);
+	sccb = kzalloc(PAGE_SIZE, GFP_KERNEL | GFP_DMA);
 	if (!sccb)
 		return -ENOMEM;
 	copied = PAGE_SIZE -
@@ -79,7 +80,7 @@ static int sclp_ctl_ioctl_sccb(void __user *user_area)
 	if (copy_to_user(u64_to_uptr(ctl_sccb.sccb), sccb, sccb->length))
 		rc = -EFAULT;
 out_free:
-	free_page((unsigned long) sccb);
+	kfree(sccb);
 	return rc;
 }
 

-- 
2.53.0