Re: [PATCH v2 2/2] lib/raid6: use kvmalloc() in raid6_select_algo()

[Andrew Morton]

On Tue, 26 May 2026 15:50:39 +0300 "Mike Rapoport (Microsoft)" <rppt@xxxxxxxxxx> wrote:

> raid6_select_algo() allocates an order 3 (8 pages) buffer that is used
> as a scratch area for selection of the best algorithm.
> 
> This buffer does not need to be physically contiguous and can be
> allocated with kvmalloc().
> 
> Replace __get_free_pages() call with kvmalloc().

This one needed some massaging due to hch's "cleanup the RAID6 P/Q
library" in mm-nonmm-unstable
(https://lore.kernel.org/20260518051804.462141-1-hch@xxxxxx)


From: "Mike Rapoport (Microsoft)" <rppt@xxxxxxxxxx>
Subject: lib/raid6: use kvmalloc() in raid6_select_algo()
Date: Tue, 26 May 2026 15:50:39 +0300

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

This buffer does not need to be physically contiguous and can be
allocated with kvmalloc().

Replace __get_free_pages() call with kvmalloc().

Link: https://lore.kernel.org/all/635405e4-9423-4a25-a6e7-e03c8ea0bcbe@xxxxxxxxxx
Link: https://lore.kernel.org/20260526-lib-v2-2-ca3f0fc24b14@xxxxxxxxxx
Signed-off-by: Mike Rapoport (Microsoft) <rppt@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 lib/raid/raid6/algos.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/lib/raid/raid6/algos.c~lib-raid6-use-kvmalloc-in-raid6_select_algo
+++ a/lib/raid/raid6/algos.c
@@ -7,6 +7,7 @@
 
 #include <linux/module.h>
 #include <linux/gfp.h>
+#include <linux/slab.h>
 #include <linux/raid/pq.h>
 #include <linux/static_call.h>
 #include <kunit/visibility.h>
@@ -153,7 +154,6 @@ EXPORT_SYMBOL_GPL(raid6_recov_datap);
 
 #define RAID6_TIME_JIFFIES_LG2	4
 #define RAID6_TEST_DISKS	8
-#define RAID6_TEST_DISKS_ORDER	3
 
 static int raid6_choose_gen(void *(*const dptrs)[RAID6_TEST_DISKS],
 		const int disks)
@@ -247,7 +247,7 @@ static int __init raid6_select_algo(void
 	}
 
 	/* prepare the buffer and fill it circularly with gfmul table */
-	disk_ptr = (char *)__get_free_pages(GFP_KERNEL, RAID6_TEST_DISKS_ORDER);
+	disk_ptr = kvmalloc(PAGE_SIZE * RAID6_TEST_DISKS, GFP_KERNEL);
 	if (!disk_ptr) {
 		pr_err("raid6: Yikes!  No memory available.\n");
 		return -ENOMEM;
@@ -269,7 +269,7 @@ static int __init raid6_select_algo(void
 	/* select raid gen_syndrome function */
 	error = raid6_choose_gen(&dptrs, disks);
 
-	free_pages((unsigned long)disk_ptr, RAID6_TEST_DISKS_ORDER);
+	kvfree(disk_ptr);
 
 	return error;
 }
_