Re: [PATCH v3 2/4] scsi: host: allocate struct Scsi_Host on the NUMA node of the host adapter

[John Garry <john.g.garry@xxxxxxxxxx>]

On 09/06/2026 13:18, Sumit Saxena wrote:
> scsi_host_alloc() used kzalloc(), which always picks an arbitrary node.
> Extend the function to accept a 'struct device *dev' parameter and use
> kzalloc_node() with dev_to_node(dev) so the Scsi_Host struct lands on
> the same NUMA node as the HBA, mirroring the treatment already applied
> to struct scsi_device, struct scsi_target, and shost_data.
>
> When dev is NULL (legacy ISA/platform drivers without a dma_dev) the
> allocation falls back to NUMA_NO_NODE, preserving existing behaviour.
>
> Update all in-tree callers:
>    - PCI-based HBA drivers pass &pdev->dev (or the equivalent struct
>      member such as &phba->pcidev->dev, &h->pdev->dev, &ha->pdev->dev)
>      so their host struct is placed on the adapter's node.
>    - Non-PCI drivers (ISA, Amiga, ARM PCMCIA, virtio, Hyper-V, PS3, …)
>      pass NULL.
>    - libfc's libfc_host_alloc() inline helper passes NULL; FC drivers
>      that want NUMA awareness can open-code the call with their pdev.
>
> Suggested-by: John Garry <john.g.garry@xxxxxxxxxx>
> Signed-off-by: Sumit Saxena <sumit.saxena@xxxxxxxxxxxx>
Wow ... I was not expecting such a large change, but admittedly I did 
not consider the implementation.
I did mention that pci-based adapters should already be effectively 
doing kzalloc_node() since the adapter driver is probed on the local 
NUMA node (and kmalloc first tries local NUMA allocations).
> ---
> diff --git a/drivers/scsi/hosts.c b/drivers/scsi/hosts.c
> index e047747d4ecf..e1f42be79729 100644
> --- a/drivers/scsi/hosts.c
> +++ b/drivers/scsi/hosts.c
> @@ -403,12 +403,14 @@ static const struct device_type scsi_host_type = {
>    * Return value:
>    *    Pointer to a new Scsi_Host
>    **/
> -struct Scsi_Host *scsi_host_alloc(const struct scsi_host_template *sht, int 
> privsize)
> +struct Scsi_Host *scsi_host_alloc(const struct scsi_host_template *sht, int 
> privsize,
> +                                 struct device *dev)
>   {
>         struct Scsi_Host *shost;
>         int index;
>   
> -	shost = kzalloc(sizeof(struct Scsi_Host) + privsize, GFP_KERNEL);
> +       shost = kzalloc_node(sizeof(struct Scsi_Host) + privsize, GFP_KERNEL,
> +                            dev ? dev_to_node(dev) : NUMA_NO_NODE);
>         if (!shost)
>                 return NULL;
>   
> -extern struct Scsi_Host *scsi_host_alloc(const struct scsi_host_template *, 
> int);
> +extern struct Scsi_Host *scsi_host_alloc(const struct scsi_host_template *sht,
> +                                        int privsize, struct device *dev);
>   extern int __must_check scsi_add_host_with_dma(struct Scsi_Host *,
>                                                struct device *,
>                                                struct device *);

scsi_add_host_with_dma() and scsi_add_host() do assignment of 
shost->dma_dev, so I think that could be moved to scsi_host_alloc().
I can imagine that we always know dev and dma_dev at Scsi_Host alloc 
time (and not just scsi_add_host()) time. However those would be very 
intrusive changes.
Let me consider this more. Maybe we can have a platform device version 
of shost alloc, as I can't imagine that we care about much more. Thanks!