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

[Denis Kirjanov]

On 12/23/15, David Gibson <david at gibson.dropbear.id.au> wrote:
> On Tue, Dec 22, 2015 at 02:19:20PM +0300, Denis Kirjanov wrote:
>> 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?
>
> Uh.. good question.  That's a not particularly useful debug comment I
> should just remove anyway.
>
>> > +
>> > +	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?
>
> No.  Failing to register this sysfs file shouldn't cause the boot to fail.
Then we don't need rc at all ;)
>
>> > +}
>> > +machine_device_initcall(pseries, pseries_lpar_sysfs);
>> >
>> > _______________________________________________
>> > Linuxppc-dev mailing list
>> > Linuxppc-dev at lists.ozlabs.org
>> > https://lists.ozlabs.org/listinfo/linuxppc-dev
>>
>
> --
> David Gibson			| I'll have my music baroque, and my code
> david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
> 				| _way_ _around_!
> http://www.ozlabs.org/~dgibson
>