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

[Mike Rapoport <rppt@kernel.org>]

On Wed, May 20, 2026 at 02:06:57PM +0100, David Laight wrote:
> 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?

Why?
 
> -- 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;
> >  }
> > 
> 
> 

-- 
Sincerely yours,
Mike.