[RFC 3/3] pseries: sysfs hack to trigger a hash page table resize

[Denis Kirjanov]

On 12/22/15, David Gibson <david at gibson.dropbear.id.au> wrote:
> This patch adds a special file in /sys/kernel/mm which can be used to view
> the current size of the hash page table (as a bit shift) and to trigger
> a resize of the hash table on PAPR guests.
>
> Logically this would make more sense as a debugfs file, but that doesn't
> see to provide an obvious way to have a "store" function that has an effect
> other than updating a variable.
>
> Signed-off-by: David Gibson <david at gibson.dropbear.id.au>
> ---
>  arch/powerpc/platforms/pseries/lpar.c | 41
> +++++++++++++++++++++++++++++++++++
>  1 file changed, 41 insertions(+)
>
> diff --git a/arch/powerpc/platforms/pseries/lpar.c
> b/arch/powerpc/platforms/pseries/lpar.c
> index aadb242..2759767 100644
> --- a/arch/powerpc/platforms/pseries/lpar.c
> +++ b/arch/powerpc/platforms/pseries/lpar.c
> @@ -903,3 +903,44 @@ int pSeries_lpar_resize_hpt(unsigned long shift)
>
>  	return 0;
>  }
> +
> +static ssize_t ppc64_pft_size_show(struct kobject *kobj,
> +				   struct kobj_attribute *attr, char *buf)
> +{
> +	return sprintf(buf, "%llu\n", (unsigned long long)ppc64_pft_size);
> +}
> +
> +static ssize_t ppc64_pft_size_store(struct kobject *kobj,
> +				    struct kobj_attribute *attr,
> +				    const char *buf, size_t count)
> +{
> +	unsigned long new_shift;
> +	int rc;
> +
> +	pr_err("lpar: ppc64_pft_size_store() count=%zd\n", count);
Why pr_err?
> +
> +	if (kstrtoul(buf, 0, &new_shift))
> +		return -EINVAL;
> +
> +	rc = pSeries_lpar_resize_hpt(new_shift);
> +	if (rc < 0)
> +		return rc;
> +
> +	return count;
> +}
> +
> +static struct kobj_attribute ppc64_pft_size_attr =
> +	__ATTR(ppc64_pft_size, 0600, ppc64_pft_size_show, ppc64_pft_size_store);
> +
> +static int __init pseries_lpar_sysfs(void)
> +{
> +	int rc;
> +
> +	rc = sysfs_create_file(mm_kobj, &ppc64_pft_size_attr.attr);
> +	if (rc)
> +		pr_err("lpar: unable to create ppc64_pft_size sysfs file (%d)\n",
> +		       rc);
> +
> +	return 0;
I think that we need to return rc value, right?
> +}
> +machine_device_initcall(pseries, pseries_lpar_sysfs);
> --
> 2.5.0
>
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