[PATCH v2] block: partitions: replace __get_free_page() with kmalloc()

[PATCH v2] block: partitions: replace __get_free_page() with kmalloc()

[Mike Rapoport (Microsoft)]

check_partition() allocates a buffer to use as backing memory for
seq_buf.

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 that does not require ugly casts and
kfree() does not need to know the size of the freed object.

For a single allocation on the cold path the 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_free_page() with kmalloc() and free_page() with
kfree().

Link: https://lore.kernel.org/all/635405e4-9423-4a25-a6e7-e03c8ea0bcbe@redhat.com
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
---
This is a (tiny) part of larger work of replacing page allocator calls
with kmalloc:

Also in git:
https://git.kernel.org/pub/scm/linux/kernel/git/rppt/linux.git gfp-to-kmalloc/block

Signed-off-by: Mike Rapoport <rppt@kernel.org>
---
v2 changes:
* reword changelog

To: Jens Axboe <axboe@kernel.dk>
Cc: linux-block@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
v1: https://patch.msgid.link/20260520-block-v1-1-6463dc2cf042@kernel.org
---
 block/partitions/core.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/block/partitions/core.c b/block/partitions/core.c
index 5d5332ce586b..b5c59b79ca7c 100644
--- a/block/partitions/core.c
+++ b/block/partitions/core.c
@@ -124,7 +124,7 @@ static struct parsed_partitions *check_partition(struct gendisk *hd)
 	state = allocate_partitions(hd);
 	if (!state)
 		return NULL;
-	state->pp_buf.buffer = (char *)__get_free_page(GFP_KERNEL);
+	state->pp_buf.buffer = kmalloc(PAGE_SIZE, GFP_KERNEL);
 	if (!state->pp_buf.buffer) {
 		free_partitions(state);
 		return NULL;
@@ -154,7 +154,7 @@ static struct parsed_partitions *check_partition(struct gendisk *hd)
 	if (res > 0) {
 		printk(KERN_INFO "%s", seq_buf_str(&state->pp_buf));
 
-		free_page((unsigned long)state->pp_buf.buffer);
+		kfree(state->pp_buf.buffer);
 		return state;
 	}
 	if (state->access_beyond_eod)
@@ -170,7 +170,7 @@ static struct parsed_partitions *check_partition(struct gendisk *hd)
 		printk(KERN_INFO "%s", seq_buf_str(&state->pp_buf));
 	}
 
-	free_page((unsigned long)state->pp_buf.buffer);
+	kfree(state->pp_buf.buffer);
 	free_partitions(state);
 	return ERR_PTR(res);
 }

---
base-commit: 5d6919055dec134de3c40167a490f33c74c12581
change-id: 20260520-block-25582753fd38

Best regards,
--  
Sincerely yours,
Mike.

Re: [PATCH v2] block: partitions: replace __get_free_page() with kmalloc()

[Jens Axboe]

On Wed, 27 May 2026 17:33:28 +0300, Mike Rapoport (Microsoft) wrote:
> check_partition() allocates a buffer to use as backing memory for
> seq_buf.
> 
> 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 that does not require ugly casts and
> kfree() does not need to know the size of the freed object.
> 
> [...]

Applied, thanks!

[1/1] block: partitions: replace __get_free_page() with kmalloc()
      commit: 17d7492a50251d913ae7101f898cf30ede856cde

Best regards,
-- 
Jens Axboe