[PATCH v3 0/2] lib/raid: replace __get_free_pages() call with kvmalloc()

[PATCH v3 0/2] lib/raid: replace __get_free_pages() call with kvmalloc()

[Mike Rapoport (Microsoft)]

This is a (tiny) part of larger work of replacing page allocator calls
with k*malloc.

Nowadays the right way to say "I need a buffer" is kmalloc() rather than
ancient and ugly __get_free_pages().

---
v3 changes:
* restore kmalloc() per Christoph
* update changelog

v2: https://patch.msgid.link/20260526-lib-v2-0-ca3f0fc24b14@kernel.org
* replace kmalloc() with kvmalloc()

v1: https://patch.msgid.link/20260520-lib-v1-0-cb3045bef2d8@kernel.org

---
Mike Rapoport (Microsoft) (2):
      xor: use kmalloc() in calibrate_xor_blocks()
      raid6: use kmalloc() in raid6_select_algo()

 lib/raid/xor/xor-core.c | 5 +++--
 lib/raid6/algos.c       | 6 +++---
 2 files changed, 6 insertions(+), 5 deletions(-)
---
base-commit: 5d6919055dec134de3c40167a490f33c74c12581
change-id: 20260520-lib-8afb92134307

Best regards,
--  
Sincerely yours,
Mike.

[PATCH v3 1/2] xor: use kmalloc() in calibrate_xor_blocks()

[Mike Rapoport (Microsoft)]

The xor benchmark allocates 4 pages for a scratch buffer that is used
purely as a CPU-only XOR working area.

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 than ancient __get_free_pages().
kmalloc() does not require ugly casts and kfree() does not need to know the
size of the freed object.

There is no performance difference because kmalloc() redirects allocations
of such size to the page allocator.

Replace __get_free_pages() call with kmalloc().

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

diff --git a/lib/raid/xor/xor-core.c b/lib/raid/xor/xor-core.c
index bd4e6e434418..7f6436774644 100644
--- a/lib/raid/xor/xor-core.c
+++ b/lib/raid/xor/xor-core.c
@@ -8,6 +8,7 @@
 
 #include <linux/module.h>
 #include <linux/gfp.h>
+#include <linux/slab.h>
 #include <linux/raid/xor.h>
 #include <linux/jiffies.h>
 #include <linux/preempt.h>
@@ -114,7 +115,7 @@ static int __init calibrate_xor_blocks(void)
 	if (forced_template)
 		return 0;
 
-	b1 = (void *) __get_free_pages(GFP_KERNEL, 2);
+	b1 = kmalloc(PAGE_SIZE * 4, GFP_KERNEL);
 	if (!b1) {
 		pr_warn("xor: Yikes!  No memory available.\n");
 		return -ENOMEM;
@@ -132,7 +133,7 @@ static int __init calibrate_xor_blocks(void)
 	pr_info("xor: using function: %s (%d MB/sec)\n",
 	       fastest->name, fastest->speed);
 
-	free_pages((unsigned long)b1, 2);
+	kvfree(b1);
 	return 0;
 }
 

-- 
2.53.0

Re: [PATCH v3 1/2] xor: use kmalloc() in calibrate_xor_blocks()

[Christoph Hellwig]

On Thu, May 28, 2026 at 10:27:55AM +0300, Mike Rapoport (Microsoft) wrote:
> -	b1 = (void *) __get_free_pages(GFP_KERNEL, 2);
> +	b1 = kmalloc(PAGE_SIZE * 4, GFP_KERNEL);
>  	if (!b1) {
>  		pr_warn("xor: Yikes!  No memory available.\n");
>  		return -ENOMEM;
> @@ -132,7 +133,7 @@ static int __init calibrate_xor_blocks(void)
>  	pr_info("xor: using function: %s (%d MB/sec)\n",
>  	       fastest->name, fastest->speed);
>  
> -	free_pages((unsigned long)b1, 2);
> +	kvfree(b1);

This should be kfree now.

Re: [PATCH v3 1/2] xor: use kmalloc() in calibrate_xor_blocks()

[Mike Rapoport]

On Thu, May 28, 2026 at 01:54:44AM -0700, Christoph Hellwig wrote:
> On Thu, May 28, 2026 at 10:27:55AM +0300, Mike Rapoport (Microsoft) wrote:
> > -	b1 = (void *) __get_free_pages(GFP_KERNEL, 2);
> > +	b1 = kmalloc(PAGE_SIZE * 4, GFP_KERNEL);
> >  	if (!b1) {
> >  		pr_warn("xor: Yikes!  No memory available.\n");
> >  		return -ENOMEM;
> > @@ -132,7 +133,7 @@ static int __init calibrate_xor_blocks(void)
> >  	pr_info("xor: using function: %s (%d MB/sec)\n",
> >  	       fastest->name, fastest->speed);
> >  
> > -	free_pages((unsigned long)b1, 2);
> > +	kvfree(b1);
> 
> This should be kfree now.

kvfree still works, but I'll send v4 for pedantry sake ;-P

-- 
Sincerely yours,
Mike.

[PATCH v3 2/2] raid6: use kmalloc() in raid6_select_algo()

[Mike Rapoport (Microsoft)]

raid6_select_algo() allocates 8 pages for buffer that is used
as a scratch area for selection of the best algorithm.

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 than ancient __get_free_pages().
kmalloc() does not require ugly casts and kfree() does not need to know the
size of the freed object.

There is no performance difference because kmalloc() redirects allocations
of such size to the page allocator.

Replace __get_free_pages() call with kmalloc().

Link: https://lore.kernel.org/all/635405e4-9423-4a25-a6e7-e03c8ea0bcbe@redhat.com
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
---
 lib/raid6/algos.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/lib/raid6/algos.c b/lib/raid6/algos.c
index 799e0e5eac26..89e627c62e30 100644
--- a/lib/raid6/algos.c
+++ b/lib/raid6/algos.c
@@ -12,6 +12,7 @@
  */
 
 #include <linux/raid/pq.h>
+#include <linux/slab.h>
 #ifndef __KERNEL__
 #include <sys/mman.h>
 #include <stdio.h>
@@ -129,7 +130,6 @@ const struct raid6_recov_calls *const raid6_recov_algos[] = {
 #endif
 
 #define RAID6_TEST_DISKS	8
-#define RAID6_TEST_DISKS_ORDER	3
 
 static inline const struct raid6_recov_calls *raid6_choose_recov(void)
 {
@@ -250,7 +250,7 @@ int __init raid6_select_algo(void)
 	int i, cycle;
 
 	/* prepare the buffer and fill it circularly with gfmul table */
-	disk_ptr = (char *)__get_free_pages(GFP_KERNEL, RAID6_TEST_DISKS_ORDER);
+	disk_ptr = kmalloc(PAGE_SIZE * RAID6_TEST_DISKS, GFP_KERNEL);
 	if (!disk_ptr) {
 		pr_err("raid6: Yikes!  No memory available.\n");
 		return -ENOMEM;
@@ -275,7 +275,7 @@ int __init raid6_select_algo(void)
 	/* select raid recover functions */
 	rec_best = raid6_choose_recov();
 
-	free_pages((unsigned long)disk_ptr, RAID6_TEST_DISKS_ORDER);
+	kfree(disk_ptr);
 
 	return gen_best && rec_best ? 0 : -EINVAL;
 }

-- 
2.53.0

Re: [PATCH v3 2/2] raid6: use kmalloc() in raid6_select_algo()

[Christoph Hellwig]

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>