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

From: David Gibson <[email-masked]>
Date: Wed, 23 Dec 2015 19:45:48 +1100

On Tue, Dec 22, 2015 at 02:19:20PM +0300, Denis Kirjanov wrote:
> On 12/22/15, David Gibson <[email-masked]> 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 <[email-masked]>
> > ---
> >  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.

> > +}
> > +machine_device_initcall(pseries, pseries_lpar_sysfs);
> >
> > _______________________________________________
> > Linuxppc-dev mailing list
> > [email-masked]
> > 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