[PATCH 10/14] s390/sclp_cmd: Replace page allocator calls with kzalloc()

[Mike Rapoport (Microsoft)]

_sclp_get_core_info(), do_chp_configure() and sclp_chp_read_info()
allocate the SCCBs used to read the CPU information, to configure a
channel path and to read the channel path information.

These buffers can be allocated with kmalloc() as there's nothing special
about them 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.

While on it, allocate only the amount of memory the SCCB actually
requires in _sclp_get_core_info() rather than rounding it up to the next
power of two. An SCCB must be page aligned and kmalloc() guarantees that
the alignment of an allocation is at least its largest power of two
divisor, so the extended SCCB is still page aligned.

Replace use of __get_free_pages() and get_zeroed_page() with kzalloc()
and free_page[s]() with kfree().

Link: https://lore.kernel.org/all/635405e4-9423-4a25-a6e7-e03c8ea0bcbe@xxxxxxxxxx
Signed-off-by: Mike Rapoport (Microsoft) <rppt@xxxxxxxxxx>
---
 drivers/s390/char/sclp_cmd.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/s390/char/sclp_cmd.c b/drivers/s390/char/sclp_cmd.c
index 1dc93d945be6f..6aaf1f6a3633f 100644
--- a/drivers/s390/char/sclp_cmd.c
+++ b/drivers/s390/char/sclp_cmd.c
@@ -102,7 +102,7 @@ int _sclp_get_core_info(struct sclp_core_info *info)
 		return -EOPNOTSUPP;
 
 	length = test_facility(140) ? EXT_SCCB_READ_CPU : PAGE_SIZE;
-	sccb = (void *)__get_free_pages(GFP_KERNEL | GFP_DMA | __GFP_ZERO, get_order(length));
+	sccb = kzalloc(length, GFP_KERNEL | GFP_DMA);
 	if (!sccb)
 		return -ENOMEM;
 	sccb->header.length = length;
@@ -119,7 +119,7 @@ int _sclp_get_core_info(struct sclp_core_info *info)
 	}
 	sclp_fill_core_info(info, sccb);
 out:
-	free_pages((unsigned long)sccb, get_order(length));
+	kfree(sccb);
 	return rc;
 }
 
@@ -173,7 +173,7 @@ static int do_chp_configure(sclp_cmdw_t cmd)
 
 	if (!SCLP_HAS_CHP_RECONFIG)
 		return -EOPNOTSUPP;
-	sccb = (struct chp_cfg_sccb *)get_zeroed_page(GFP_KERNEL | GFP_DMA);
+	sccb = kzalloc(PAGE_SIZE, GFP_KERNEL | GFP_DMA);
 	if (!sccb)
 		return -ENOMEM;
 	sccb->header.length = sizeof(*sccb);
@@ -193,7 +193,7 @@ static int do_chp_configure(sclp_cmdw_t cmd)
 		break;
 	}
 out:
-	free_page((unsigned long)sccb);
+	kfree(sccb);
 	return rc;
 }
 
@@ -236,7 +236,7 @@ int sclp_chp_read_info(struct sclp_chp_info *info)
 
 	if (!SCLP_HAS_CHP_INFO)
 		return -EOPNOTSUPP;
-	sccb = (struct chp_info_sccb *)get_zeroed_page(GFP_KERNEL | GFP_DMA);
+	sccb = kzalloc(PAGE_SIZE, GFP_KERNEL | GFP_DMA);
 	if (!sccb)
 		return -ENOMEM;
 	sccb->header.length = sizeof(*sccb);
@@ -253,6 +253,6 @@ int sclp_chp_read_info(struct sclp_chp_info *info)
 	memcpy(info->standby, sccb->standby, SCLP_CHP_INFO_MASK_SIZE);
 	memcpy(info->configured, sccb->configured, SCLP_CHP_INFO_MASK_SIZE);
 out:
-	free_page((unsigned long)sccb);
+	kfree(sccb);
 	return rc;
 }

-- 
2.53.0