Re: [PATCH 4/4] sfc: use kmalloc() to allocate logging buffer

[Edward Cree <ecree.xilinx@gmail.com>]

On 01/07/2026 14:57, Mike Rapoport (Microsoft) wrote:
> efx_mcdi_init() allocates a logging buffer for MCDI firmware
> communication diagnostics.
> 
> 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_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>

Reviewed-by: Edward Cree <ecree.xilinx@gmail.com>

> ---
>  drivers/net/ethernet/sfc/mcdi.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/ethernet/sfc/mcdi.c b/drivers/net/ethernet/sfc/mcdi.c
> index e65db9b70724..b806d3d90c42 100644
> --- a/drivers/net/ethernet/sfc/mcdi.c
> +++ b/drivers/net/ethernet/sfc/mcdi.c
> @@ -7,6 +7,7 @@
>  #include <linux/delay.h>
>  #include <linux/moduleparam.h>
>  #include <linux/atomic.h>
> +#include <linux/slab.h>
>  #include "net_driver.h"
>  #include "nic.h"
>  #include "io.h"
> @@ -71,7 +72,7 @@ int efx_mcdi_init(struct efx_nic *efx)
>  	mcdi->efx = efx;
>  #ifdef CONFIG_SFC_MCDI_LOGGING
>  	/* consuming code assumes buffer is page-sized */
> -	mcdi->logging_buffer = (char *)__get_free_page(GFP_KERNEL);
> +	mcdi->logging_buffer = kmalloc(PAGE_SIZE, GFP_KERNEL);
>  	if (!mcdi->logging_buffer)
>  		goto fail1;
>  	mcdi->logging_enabled = mcdi_logging_default;
> @@ -112,7 +113,7 @@ int efx_mcdi_init(struct efx_nic *efx)
>  	return 0;
>  fail2:
>  #ifdef CONFIG_SFC_MCDI_LOGGING
> -	free_page((unsigned long)mcdi->logging_buffer);
> +	kfree(mcdi->logging_buffer);
>  fail1:
>  #endif
>  	kfree(efx->mcdi);
> @@ -138,7 +139,7 @@ void efx_mcdi_fini(struct efx_nic *efx)
>  		return;
>  
>  #ifdef CONFIG_SFC_MCDI_LOGGING
> -	free_page((unsigned long)efx->mcdi->iface.logging_buffer);
> +	kfree(efx->mcdi->iface.logging_buffer);
>  #endif
>  
>  	kfree(efx->mcdi);
>