[PATCH 01/13] s390/chsc: Use kzalloc() for CUBs

[Mike Rapoport (Microsoft)]

cub_alloc() allocates the channel measurement unit blocks and their
extended counterparts.

This memory 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@xxxxxxxxxx
Assisted-by: copilot:claude-opus
Signed-off-by: Mike Rapoport (Microsoft) <rppt@xxxxxxxxxx>
---
 drivers/s390/cio/chsc.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/s390/cio/chsc.c b/drivers/s390/cio/chsc.c
index 9689f722c863c..60a4a7e6086ce 100644
--- a/drivers/s390/cio/chsc.c
+++ b/drivers/s390/cio/chsc.c
@@ -931,12 +931,12 @@ static int cub_alloc(struct channel_subsystem *css)
 	int i;
 
 	for (i = 0; i < CSS_NUM_CUB_PAGES; i++) {
-		css->cub[i] = (void *)get_zeroed_page(GFP_KERNEL | GFP_DMA);
+		css->cub[i] = kzalloc(PAGE_SIZE, GFP_KERNEL | GFP_DMA);
 		if (!css->cub[i])
 			return -ENOMEM;
 	}
 	for (i = 0; i < CSS_NUM_ECUB_PAGES; i++) {
-		css->ecub[i] = (void *)get_zeroed_page(GFP_KERNEL);
+		css->ecub[i] = kzalloc(PAGE_SIZE, GFP_KERNEL);
 		if (!css->ecub[i])
 			return -ENOMEM;
 	}
@@ -949,11 +949,11 @@ static void cub_free(struct channel_subsystem *css)
 	int i;
 
 	for (i = 0; i < CSS_NUM_CUB_PAGES; i++) {
-		free_page((unsigned long)css->cub[i]);
+		kfree(css->cub[i]);
 		css->cub[i] = NULL;
 	}
 	for (i = 0; i < CSS_NUM_ECUB_PAGES; i++) {
-		free_page((unsigned long)css->ecub[i]);
+		kfree(css->ecub[i]);
 		css->ecub[i] = NULL;
 	}
 }

-- 
2.53.0