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

[David Laight <david.laight.linux@gmail.com>]

On Wed, 20 May 2026 11:17:52 +0300
"Mike Rapoport (Microsoft)" <rppt@kernel.org> wrote:

> raid6_select_algo() allocates an order 3 (8 pages) buffer that is used
> as a scratch area for selection of the best algorithm.

Should this code really be using a 4k buffer rather than a PAGE_SIZE one?

-- David

> 
> For such large allocations kmalloc() would fall back to alloc_pages() but
> still kmalloc() is a better API as it does not require unnecessary
> castings and may provide more debugging possibilities.
> 
> 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;
>  }
>