On Tue, Dec 22, 2015 at 02:19:20PM +0300, Denis Kirjanov wrote:

On 12/22/15, David Gibson [off-list ref] wrote:

quoted

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 <redacted>
---
 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.

quoted

+
+	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.

quoted

+}
+machine_device_initcall(pseries, pseries_lpar_sysfs);

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-- 
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