[PATCH 0/2] USB: replace __get_free_pages() with kmalloc()

[PATCH 0/2] USB: replace __get_free_pages() with kmalloc()

[Mike Rapoport (Microsoft)]

This is a (small) part of larger work of replacing page allocator calls
with kmalloc.

My initial intention a few month ago was to remove ugly casts [1], but then
willy pointed out that Linus objected to something like this [2] and it
looks like more than a decade old technical debt.

Largely, anything that doesn't need struct page (or a memdesc in the
future) should just use kmalloc() or kvmalloc() to allocate memory.
kmalloc() guarantees alignment, physical contiguity and working
virt_to_phys() and beside nicer API that returns void * on alloc and
doesn't require to know the allocation size on free, kmalloc() provides
better debugging capabilities than page allocator.

Another thing is that touching these allocation sites gives the reviewers
opportunity to see if a PAGE_SIZE buffer is actually needed or maybe
another size is appropriate.

For larger allocations that don't need physically contiguous memory
kvmalloc() can be a better option that __get_free_pages() because under
memory pressure it's is easier to allocate several order-0 pages than a
physically contiguous chunk with the same number of pages.

And last, but not least, removing needless calls to page allocator should
help with memdesc (aka project folio) conversion. There will be way less
places to audit to see if the user was actually using struct page.

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

[1] https://lore.kernel.org/all/20251018093002.3660549-1-rppt@kernel.org/
[2] https://lore.kernel.org/all/CA+55aFwp4iy4rtX2gE2WjBGFL=NxMVnoFeHqYa2j1dYOMMGqxg@mail.gmail.com/

---
Mike Rapoport (Microsoft) (2):
      usb: host: ohci-dbg: use kmalloc() for print buffer
      usb: core: devices: use kmalloc() to allocate dump buffer

 drivers/usb/core/devices.c  |  7 ++++---
 drivers/usb/host/ohci-dbg.c | 11 ++++-------
 2 files changed, 8 insertions(+), 10 deletions(-)
---
base-commit: dc59e4fea9d83f03bad6bddf3fa2e52491777482
change-id: 20260616-b4-usb-b302cae4004d

Best regards,
--  
Sincerely yours,
Mike.

[PATCH 1/2] usb: host: ohci-dbg: use kmalloc() for print buffer

[Mike Rapoport (Microsoft)]

ochi-dbg allocates buffers for formatting of various dump outputs.

These buffers can be allocated with kmalloc() as there's nothing special
about them 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.

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_zeroed_page() with kzalloc() and free_page() with
kfree().

While on it, make kfree() calls unconditional since kfree() can be passed a
NULL pointer.

Link: https://lore.kernel.org/all/635405e4-9423-4a25-a6e7-e03c8ea0bcbe@redhat.com
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
---
 drivers/usb/host/ohci-dbg.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/drivers/usb/host/ohci-dbg.c b/drivers/usb/host/ohci-dbg.c
index 9e0e06bbc570..0a648a7d9136 100644
--- a/drivers/usb/host/ohci-dbg.c
+++ b/drivers/usb/host/ohci-dbg.c
@@ -1,4 +1,5 @@
 // SPDX-License-Identifier: GPL-1.0+
+#include <linux/slab.h>
 /*
  * OHCI HCD (Host Controller Driver) for USB.
  *
@@ -683,7 +684,7 @@ static int fill_buffer(struct debug_buffer *buf)
 	int ret;
 
 	if (!buf->page)
-		buf->page = (char *)get_zeroed_page(GFP_KERNEL);
+		buf->page = kzalloc(PAGE_SIZE, GFP_KERNEL);
 
 	if (!buf->page) {
 		ret = -ENOMEM;
@@ -729,11 +730,8 @@ static int debug_close(struct inode *inode, struct file *file)
 {
 	struct debug_buffer *buf = file->private_data;
 
-	if (buf) {
-		if (buf->page)
-			free_page((unsigned long)buf->page);
-		kfree(buf);
-	}
+	kfree(buf->page);
+	kfree(buf);
 
 	return 0;
 }
@@ -782,4 +780,3 @@ static inline void remove_debug_files (struct ohci_hcd *ohci)
 }
 
 /*-------------------------------------------------------------------------*/
-

-- 
2.53.0

[PATCH 2/2] usb: core: devices: use kmalloc() to allocate dump buffer

[Mike Rapoport (Microsoft)]

usb_device_dump() allocates a buffer for formatting
/proc/bus/usb/devices output text.

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.

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_pages() with kmalloc() and free_pages() with
kfree().

Link: https://lore.kernel.org/all/635405e4-9423-4a25-a6e7-e03c8ea0bcbe@redhat.com
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
---
 drivers/usb/core/devices.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/usb/core/devices.c b/drivers/usb/core/devices.c
index a247da73f34d..6f0354aba38b 100644
--- a/drivers/usb/core/devices.c
+++ b/drivers/usb/core/devices.c
@@ -37,6 +37,7 @@
  */
 
 #include <linux/fs.h>
+#include <linux/slab.h>
 #include <linux/mm.h>
 #include <linux/gfp.h>
 #include <linux/usb.h>
@@ -408,7 +409,7 @@ static ssize_t usb_device_dump(char __user **buffer, size_t *nbytes,
 		return 0;
 	/* allocate 2^1 pages = 8K (on i386);
 	 * should be more than enough for one device */
-	pages_start = (char *)__get_free_pages(GFP_NOIO, 1);
+	pages_start = kmalloc(PAGE_SIZE << 1, GFP_NOIO);
 	if (!pages_start)
 		return -ENOMEM;
 
@@ -479,7 +480,7 @@ static ssize_t usb_device_dump(char __user **buffer, size_t *nbytes,
 		if (length > *nbytes)
 			length = *nbytes;
 		if (copy_to_user(*buffer, pages_start + *skip_bytes, length)) {
-			free_pages((unsigned long)pages_start, 1);
+			kfree(pages_start);
 			return -EFAULT;
 		}
 		*nbytes -= length;
@@ -490,7 +491,7 @@ static ssize_t usb_device_dump(char __user **buffer, size_t *nbytes,
 	} else
 		*skip_bytes -= length;
 
-	free_pages((unsigned long)pages_start, 1);
+	kfree(pages_start);
 
 	/* Now look at all of this device's children. */
 	usb_hub_for_each_child(usbdev, chix, childdev) {

-- 
2.53.0

Re: [PATCH 1/2] usb: host: ohci-dbg: use kmalloc() for print buffer

[Alan Stern]

On Tue, Jun 30, 2026 at 01:27:08PM +0300, Mike Rapoport (Microsoft) wrote:
> ochi-dbg allocates buffers for formatting of various dump outputs.
> 
> These buffers can be allocated with kmalloc() as there's nothing special
> about them 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.
> 
> 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_zeroed_page() with kzalloc() and free_page() with
> kfree().
> 
> While on it, make kfree() calls unconditional since kfree() can be passed a
> NULL pointer.

That is not a good way of describing the last change.  The 
"kfree(buf->page)" call may indeed pass a NULL pointer, but the fact 
that it doesn't dereference a NULL pointer (i.e., buf) is not obvious.

> Link: https://lore.kernel.org/all/635405e4-9423-4a25-a6e7-e03c8ea0bcbe@redhat.com
> Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
> ---
>  drivers/usb/host/ohci-dbg.c | 11 ++++-------
>  1 file changed, 4 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/usb/host/ohci-dbg.c b/drivers/usb/host/ohci-dbg.c
> index 9e0e06bbc570..0a648a7d9136 100644
> --- a/drivers/usb/host/ohci-dbg.c
> +++ b/drivers/usb/host/ohci-dbg.c
> @@ -1,4 +1,5 @@
>  // SPDX-License-Identifier: GPL-1.0+
> +#include <linux/slab.h>

Thanks to the odd way in which ohci-hcd is built, this line is 
completely unnecessary.  It should not be part of the patch.

Alan Stern

>  /*
>   * OHCI HCD (Host Controller Driver) for USB.
>   *
> @@ -683,7 +684,7 @@ static int fill_buffer(struct debug_buffer *buf)
>  	int ret;
>  
>  	if (!buf->page)
> -		buf->page = (char *)get_zeroed_page(GFP_KERNEL);
> +		buf->page = kzalloc(PAGE_SIZE, GFP_KERNEL);
>  
>  	if (!buf->page) {
>  		ret = -ENOMEM;
> @@ -729,11 +730,8 @@ static int debug_close(struct inode *inode, struct file *file)
>  {
>  	struct debug_buffer *buf = file->private_data;
>  
> -	if (buf) {
> -		if (buf->page)
> -			free_page((unsigned long)buf->page);
> -		kfree(buf);
> -	}
> +	kfree(buf->page);
> +	kfree(buf);
>  
>  	return 0;
>  }
> @@ -782,4 +780,3 @@ static inline void remove_debug_files (struct ohci_hcd *ohci)
>  }
>  
>  /*-------------------------------------------------------------------------*/
> -
> 
> -- 
> 2.53.0
> 

Re: [PATCH 2/2] usb: core: devices: use kmalloc() to allocate dump buffer

[Alan Stern]

On Tue, Jun 30, 2026 at 01:27:09PM +0300, Mike Rapoport (Microsoft) wrote:
> usb_device_dump() allocates a buffer for formatting
> /proc/bus/usb/devices output text.

You mean /sys/kernel/debug/usb/devices.  There is no /proc/bus/usb/ 
directory.

Aside from that mistake:

Reviewed-by: Alan Stern <stern@rowland.harvard.edu>

Alan Stern

> 
> 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.
> 
> 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_pages() with kmalloc() and free_pages() with
> kfree().
> 
> Link: https://lore.kernel.org/all/635405e4-9423-4a25-a6e7-e03c8ea0bcbe@redhat.com
> Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
> ---
>  drivers/usb/core/devices.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/usb/core/devices.c b/drivers/usb/core/devices.c
> index a247da73f34d..6f0354aba38b 100644
> --- a/drivers/usb/core/devices.c
> +++ b/drivers/usb/core/devices.c
> @@ -37,6 +37,7 @@
>   */
>  
>  #include <linux/fs.h>
> +#include <linux/slab.h>
>  #include <linux/mm.h>
>  #include <linux/gfp.h>
>  #include <linux/usb.h>
> @@ -408,7 +409,7 @@ static ssize_t usb_device_dump(char __user **buffer, size_t *nbytes,
>  		return 0;
>  	/* allocate 2^1 pages = 8K (on i386);
>  	 * should be more than enough for one device */
> -	pages_start = (char *)__get_free_pages(GFP_NOIO, 1);
> +	pages_start = kmalloc(PAGE_SIZE << 1, GFP_NOIO);
>  	if (!pages_start)
>  		return -ENOMEM;
>  
> @@ -479,7 +480,7 @@ static ssize_t usb_device_dump(char __user **buffer, size_t *nbytes,
>  		if (length > *nbytes)
>  			length = *nbytes;
>  		if (copy_to_user(*buffer, pages_start + *skip_bytes, length)) {
> -			free_pages((unsigned long)pages_start, 1);
> +			kfree(pages_start);
>  			return -EFAULT;
>  		}
>  		*nbytes -= length;
> @@ -490,7 +491,7 @@ static ssize_t usb_device_dump(char __user **buffer, size_t *nbytes,
>  	} else
>  		*skip_bytes -= length;
>  
> -	free_pages((unsigned long)pages_start, 1);
> +	kfree(pages_start);
>  
>  	/* Now look at all of this device's children. */
>  	usb_hub_for_each_child(usbdev, chix, childdev) {
> 
> -- 
> 2.53.0
>