[PATCH 0/6] powerpc: Hash Page Table resizing for PAPR guests

[PATCH 0/6] powerpc: Hash Page Table resizing for PAPR guests

[David Gibson]

This series implements the guest side of a PAPR ACR which allows a
POWER guest's Hashed Page Table (HPT) to be resized at runtime.  This
is useful when a guest has a very large theoretical maximum RAM, but
is likely to only ever be expanded to a modest amount of RAM in
practice.  Without resizing the HPT has to be sized for the maximum
possible guest RAM, which can be very wasteful if that maximum is
never reached.

To use this requires a hypervisor/host which also supports the PAPR
extension.  The only implementation so far is my qemu branch at
    https://github.com/dgibson/qemu/tree/upstream/hpt-resize
    
I expect to merge that code to upstream qemu for qemu-2.9.  Note that
HPT resizing will so far only work for TCG guests, KVM support is in
the works.  The guest side code here will not require changing for
KVM, however.

An HPT resize can be triggered in one of two ways:
    * /sys/kernel/debug/powerpc/pft-size

        This debugfs file contains the current size of the HPT (as
        encoded in the ibm,pft-size) device tree property.  Writing to
        it will cause the guest to attempt an HPT resize to the given
        value.  Note that the current qemu implementation will not
        allow the guest to resize the HPT to more than 1/64th of guest
        RAM size.

    * Automatically on memory hotplug / unplug

        With these patches applied, the guest will automatically
        attempt to resize its HPT when its RAM size changes due to
        hotplug events.  (When hot adding RAM qemu considers the new
        size for purposes of the limit mentioned above, so this method
        can lift the HPT size larger than the former).

David Gibson (6):
  kvm: Move KVM_PPC_PVINFO_FLAGS_EV_IDLE definition next to its
    structure
  powerpc/kvm: Corectly report KVM_CAP_PPC_ALLOC_HTAB
  pseries: Add hypercall wrappers for hash page table resizing
  pseries: Add support for hash table resizing
  pseries: Advertise HPT resizing support via CAS
  pseries: Automatically resize HPT for memory hot add/remove

 arch/powerpc/include/asm/book3s/64/mmu-hash.h |   1 +
 arch/powerpc/include/asm/firmware.h           |   5 +-
 arch/powerpc/include/asm/hvcall.h             |   4 +-
 arch/powerpc/include/asm/plpar_wrappers.h     |  12 +++
 arch/powerpc/include/asm/prom.h               |   1 +
 arch/powerpc/include/asm/sparsemem.h          |   1 +
 arch/powerpc/kernel/prom_init.c               |   2 +-
 arch/powerpc/kvm/powerpc.c                    |   5 +-
 arch/powerpc/mm/hash_utils_64.c               |  57 +++++++++++++
 arch/powerpc/mm/mem.c                         |   4 +
 arch/powerpc/platforms/pseries/firmware.c     |   1 +
 arch/powerpc/platforms/pseries/lpar.c         | 110 ++++++++++++++++++++++++++
 include/uapi/linux/kvm.h                      |   5 +-
 13 files changed, 201 insertions(+), 7 deletions(-)

-- 
2.9.3

[PATCH 1/6] kvm: Move KVM_PPC_PVINFO_FLAGS_EV_IDLE definition next to its structure

[David Gibson]

The KVM_PPC_PVINFO_FLAGS_EV_IDLE macro defines a bit for use in the flags
field of struct kvm_ppc_pvinfo.  However, changes since that was introduced
have moved it away from that structure definition, which is confusing.

Move it back next to the structure it belongs with.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 include/uapi/linux/kvm.h | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 4ee67cb..cac48ed 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -651,6 +651,9 @@ struct kvm_enable_cap {
 };
 
 /* for KVM_PPC_GET_PVINFO */
+
+#define KVM_PPC_PVINFO_FLAGS_EV_IDLE   (1<<0)
+
 struct kvm_ppc_pvinfo {
 	/* out */
 	__u32 flags;
@@ -682,8 +685,6 @@ struct kvm_ppc_smmu_info {
 	struct kvm_ppc_one_seg_page_size sps[KVM_PPC_PAGE_SIZES_MAX_SZ];
 };
 
-#define KVM_PPC_PVINFO_FLAGS_EV_IDLE   (1<<0)
-
 #define KVMIO 0xAE
 
 /* machine type bits, to be used as argument to KVM_CREATE_VM */
-- 
2.9.3

[PATCH 2/6] powerpc/kvm: Corectly report KVM_CAP_PPC_ALLOC_HTAB

[David Gibson]

At present KVM on powerpc always reports KVM_CAP_PPC_ALLOC_HTAB as enabled.
However, the ioctl() it advertises (KVM_PPC_ALLOCATE_HTAB) only actually
works on KVM HV.  On KVM PR it will fail with ENOTTY.

qemu already has a workaround for this, so it's not breaking things in
practice, but it would be better to advertise this correctly.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 arch/powerpc/kvm/powerpc.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
index 70963c8..7b6b9eb 100644
--- a/arch/powerpc/kvm/powerpc.c
+++ b/arch/powerpc/kvm/powerpc.c
@@ -536,7 +536,6 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 #ifdef CONFIG_PPC_BOOK3S_64
 	case KVM_CAP_SPAPR_TCE:
 	case KVM_CAP_SPAPR_TCE_64:
-	case KVM_CAP_PPC_ALLOC_HTAB:
 	case KVM_CAP_PPC_RTAS:
 	case KVM_CAP_PPC_FIXUP_HCALL:
 	case KVM_CAP_PPC_ENABLE_HCALL:
@@ -545,6 +544,10 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 #endif
 		r = 1;
 		break;
+
+	case KVM_CAP_PPC_ALLOC_HTAB:
+		r = hv_enabled;
+		break;
 #endif /* CONFIG_PPC_BOOK3S_64 */
 #ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
 	case KVM_CAP_PPC_SMT:
-- 
2.9.3

[PATCH 3/6] pseries: Add hypercall wrappers for hash page table resizing

[David Gibson]

This adds the hypercall numbers and wrapper functions for the hash page
table resizing hypercalls.

These are experimental "platform specific" values for now, until we have a
formal PAPR update.

It also adds a new firmware feature flag to track the presence of the
HPT resizing calls.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Paul Mackerras <paulus@samba.org>
---
 arch/powerpc/include/asm/firmware.h       |  5 +++--
 arch/powerpc/include/asm/hvcall.h         |  4 +++-
 arch/powerpc/include/asm/plpar_wrappers.h | 12 ++++++++++++
 arch/powerpc/platforms/pseries/firmware.c |  1 +
 4 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/include/asm/firmware.h b/arch/powerpc/include/asm/firmware.h
index 1e0b5a5..8645897 100644
--- a/arch/powerpc/include/asm/firmware.h
+++ b/arch/powerpc/include/asm/firmware.h
@@ -42,7 +42,7 @@
 #define FW_FEATURE_SPLPAR	ASM_CONST(0x0000000000100000)
 #define FW_FEATURE_LPAR		ASM_CONST(0x0000000000400000)
 #define FW_FEATURE_PS3_LV1	ASM_CONST(0x0000000000800000)
-/* Free				ASM_CONST(0x0000000001000000) */
+#define FW_FEATURE_HPT_RESIZE	ASM_CONST(0x0000000001000000)
 #define FW_FEATURE_CMO		ASM_CONST(0x0000000002000000)
 #define FW_FEATURE_VPHN		ASM_CONST(0x0000000004000000)
 #define FW_FEATURE_XCMO		ASM_CONST(0x0000000008000000)
@@ -66,7 +66,8 @@ enum {
 		FW_FEATURE_MULTITCE | FW_FEATURE_SPLPAR | FW_FEATURE_LPAR |
 		FW_FEATURE_CMO | FW_FEATURE_VPHN | FW_FEATURE_XCMO |
 		FW_FEATURE_SET_MODE | FW_FEATURE_BEST_ENERGY |
-		FW_FEATURE_TYPE1_AFFINITY | FW_FEATURE_PRRN,
+		FW_FEATURE_TYPE1_AFFINITY | FW_FEATURE_PRRN |
+		FW_FEATURE_HPT_RESIZE,
 	FW_FEATURE_PSERIES_ALWAYS = 0,
 	FW_FEATURE_POWERNV_POSSIBLE = FW_FEATURE_OPAL,
 	FW_FEATURE_POWERNV_ALWAYS = 0,
diff --git a/arch/powerpc/include/asm/hvcall.h b/arch/powerpc/include/asm/hvcall.h
index 708edeb..9b7ff7c 100644
--- a/arch/powerpc/include/asm/hvcall.h
+++ b/arch/powerpc/include/asm/hvcall.h
@@ -275,7 +275,9 @@
 #define H_COP			0x304
 #define H_GET_MPP_X		0x314
 #define H_SET_MODE		0x31C
-#define MAX_HCALL_OPCODE	H_SET_MODE
+#define H_RESIZE_HPT_PREPARE	0x36C
+#define H_RESIZE_HPT_COMMIT	0x370
+#define MAX_HCALL_OPCODE	H_RESIZE_HPT_COMMIT
 
 /* H_VIOCTL functions */
 #define H_GET_VIOA_DUMP_SIZE	0x01
diff --git a/arch/powerpc/include/asm/plpar_wrappers.h b/arch/powerpc/include/asm/plpar_wrappers.h
index 1b39424..b7ee6d9 100644
--- a/arch/powerpc/include/asm/plpar_wrappers.h
+++ b/arch/powerpc/include/asm/plpar_wrappers.h
@@ -242,6 +242,18 @@ static inline long plpar_pte_protect(unsigned long flags, unsigned long ptex,
 	return plpar_hcall_norets(H_PROTECT, flags, ptex, avpn);
 }
 
+static inline long plpar_resize_hpt_prepare(unsigned long flags,
+					    unsigned long shift)
+{
+	return plpar_hcall_norets(H_RESIZE_HPT_PREPARE, flags, shift);
+}
+
+static inline long plpar_resize_hpt_commit(unsigned long flags,
+					   unsigned long shift)
+{
+	return plpar_hcall_norets(H_RESIZE_HPT_COMMIT, flags, shift);
+}
+
 static inline long plpar_tce_get(unsigned long liobn, unsigned long ioba,
 		unsigned long *tce_ret)
 {
diff --git a/arch/powerpc/platforms/pseries/firmware.c b/arch/powerpc/platforms/pseries/firmware.c
index ea7f09b..658c02d 100644
--- a/arch/powerpc/platforms/pseries/firmware.c
+++ b/arch/powerpc/platforms/pseries/firmware.c
@@ -64,6 +64,7 @@ hypertas_fw_features_table[] = {
 	{FW_FEATURE_VPHN,		"hcall-vphn"},
 	{FW_FEATURE_SET_MODE,		"hcall-set-mode"},
 	{FW_FEATURE_BEST_ENERGY,	"hcall-best-energy-1*"},
+	{FW_FEATURE_HPT_RESIZE,		"hcall-hpt-resize"},
 };
 
 /* Build up the firmware features bitmask using the contents of
-- 
2.9.3

[PATCH 4/6] pseries: Add support for hash table resizing

[David Gibson]

This adds support for using experimental hypercalls to change the size
of the main hash page table while running as a PAPR guest.  For now these
hypercalls are only in experimental qemu versions.

The interface is two part: first H_RESIZE_HPT_PREPARE is used to allocate
and prepare the new hash table.  This may be slow, but can be done
asynchronously.  Then, H_RESIZE_HPT_COMMIT is used to switch to the new
hash table.  This requires that no CPUs be concurrently updating the HPT,
and so must be run under stop_machine().

This also adds a debugfs file which can be used to manually control
HPT resizing or testing purposes.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Paul Mackerras <paulus@samba.org>
---
 arch/powerpc/include/asm/book3s/64/mmu-hash.h |   1 +
 arch/powerpc/mm/hash_utils_64.c               |  28 +++++++
 arch/powerpc/platforms/pseries/lpar.c         | 110 ++++++++++++++++++++++++++
 3 files changed, 139 insertions(+)

diff --git a/arch/powerpc/include/asm/book3s/64/mmu-hash.h b/arch/powerpc/include/asm/book3s/64/mmu-hash.h
index e407af2..efba649 100644
--- a/arch/powerpc/include/asm/book3s/64/mmu-hash.h
+++ b/arch/powerpc/include/asm/book3s/64/mmu-hash.h
@@ -153,6 +153,7 @@ struct mmu_hash_ops {
 					       unsigned long addr,
 					       unsigned char *hpte_slot_array,
 					       int psize, int ssize, int local);
+	int		(*resize_hpt)(unsigned long shift);
 	/*
 	 * Special for kexec.
 	 * To be called in real mode with interrupts disabled. No locks are
diff --git a/arch/powerpc/mm/hash_utils_64.c b/arch/powerpc/mm/hash_utils_64.c
index 78dabf06..474da2e 100644
--- a/arch/powerpc/mm/hash_utils_64.c
+++ b/arch/powerpc/mm/hash_utils_64.c
@@ -35,6 +35,7 @@
 #include <linux/memblock.h>
 #include <linux/context_tracking.h>
 #include <linux/libfdt.h>
+#include <linux/debugfs.h>
 
 #include <asm/processor.h>
 #include <asm/pgtable.h>
@@ -1815,3 +1816,30 @@ void hash__setup_initial_memory_limit(phys_addr_t first_memblock_base,
 	/* Finally limit subsequent allocations */
 	memblock_set_current_limit(ppc64_rma_size);
 }
+
+static int ppc64_pft_size_get(void *data, u64 *val)
+{
+	*val = ppc64_pft_size;
+	return 0;
+}
+
+static int ppc64_pft_size_set(void *data, u64 val)
+{
+	if (!mmu_hash_ops.resize_hpt)
+		return -ENODEV;
+	return mmu_hash_ops.resize_hpt(val);
+}
+
+DEFINE_SIMPLE_ATTRIBUTE(fops_ppc64_pft_size,
+			ppc64_pft_size_get, ppc64_pft_size_set,	"%llu\n");
+
+static int __init hash64_debugfs(void)
+{
+	if (!debugfs_create_file("pft-size", 0600, powerpc_debugfs_root,
+				 NULL, &fops_ppc64_pft_size)) {
+		pr_err("lpar: unable to create ppc64_pft_size debugsfs file\n");
+	}
+
+	return 0;
+}
+machine_device_initcall(pseries, hash64_debugfs);
diff --git a/arch/powerpc/platforms/pseries/lpar.c b/arch/powerpc/platforms/pseries/lpar.c
index aa35245..5f0cee3 100644
--- a/arch/powerpc/platforms/pseries/lpar.c
+++ b/arch/powerpc/platforms/pseries/lpar.c
@@ -27,6 +27,8 @@
 #include <linux/console.h>
 #include <linux/export.h>
 #include <linux/jump_label.h>
+#include <linux/delay.h>
+#include <linux/stop_machine.h>
 #include <asm/processor.h>
 #include <asm/mmu.h>
 #include <asm/page.h>
@@ -589,6 +591,113 @@ static int __init disable_bulk_remove(char *str)
 
 __setup("bulk_remove=", disable_bulk_remove);
 
+#define HPT_RESIZE_TIMEOUT	10000 /* ms */
+
+struct hpt_resize_state {
+	unsigned long shift;
+	int commit_rc;
+};
+
+static int pseries_lpar_resize_hpt_commit(void *data)
+{
+	struct hpt_resize_state *state = data;
+
+	state->commit_rc = plpar_resize_hpt_commit(0, state->shift);
+	if (state->commit_rc != H_SUCCESS)
+		return -EIO;
+
+	/* Hypervisor has transitioned the HTAB, update our globals */
+	ppc64_pft_size = state->shift;
+	htab_size_bytes = 1UL << ppc64_pft_size;
+	htab_hash_mask = (htab_size_bytes >> 7) - 1;
+
+	return 0;
+}
+
+/* Must be called in user context */
+static int pseries_lpar_resize_hpt(unsigned long shift)
+{
+	struct hpt_resize_state state = {
+		.shift = shift,
+		.commit_rc = H_FUNCTION,
+	};
+	unsigned int delay, total_delay = 0;
+	int rc;
+	ktime_t t0, t1, t2;
+
+	might_sleep();
+
+	if (!firmware_has_feature(FW_FEATURE_HPT_RESIZE))
+		return -ENODEV;
+
+	printk(KERN_INFO "lpar: Attempting to resize HPT to shift %lu\n",
+	       shift);
+
+	t0 = ktime_get();
+
+	rc = plpar_resize_hpt_prepare(0, shift);
+	while (H_IS_LONG_BUSY(rc)) {
+		delay = get_longbusy_msecs(rc);
+		total_delay += delay;
+		if (total_delay > HPT_RESIZE_TIMEOUT) {
+			/* prepare call with shift==0 cancels an
+			 * in-progress resize */
+			rc = plpar_resize_hpt_prepare(0, 0);
+			if (rc != H_SUCCESS)
+				printk(KERN_WARNING
+				       "lpar: Unexpected error %d cancelling timed out HPT resize\n",
+				       rc);
+			return -ETIMEDOUT;
+		}
+		msleep(delay);
+		rc = plpar_resize_hpt_prepare(0, shift);
+	};
+
+	switch (rc) {
+	case H_SUCCESS:
+		/* Continue on */
+		break;
+
+	case H_PARAMETER:
+		return -EINVAL;
+	case H_RESOURCE:
+		return -EPERM;
+	default:
+		printk(KERN_WARNING
+		       "lpar: Unexpected error %d from H_RESIZE_HPT_PREPARE\n",
+		       rc);
+		return -EIO;
+	}
+
+	t1 = ktime_get();
+
+	rc = stop_machine(pseries_lpar_resize_hpt_commit, &state, NULL);
+
+	t2 = ktime_get();
+
+	if (rc != 0) {
+		switch (state.commit_rc) {
+		case H_PTEG_FULL:
+			printk(KERN_WARNING
+			       "lpar: Hash collision while resizing HPT\n");
+			return -ENOSPC;
+
+		default:
+			printk(KERN_WARNING
+			       "lpar: Unexpected error %d from H_RESIZE_HPT_COMMIT\n",
+			       state.commit_rc);
+			return -EIO;
+		};
+	}
+
+	printk(KERN_INFO
+	       "lpar: HPT resize to shift %lu complete (%lld ms / %lld ms)\n",
+	       shift, (long long) ktime_ms_delta(t1, t0),
+	       (long long) ktime_ms_delta(t2, t1));
+
+	return 0;
+}
+
 void __init hpte_init_pseries(void)
 {
 	mmu_hash_ops.hpte_invalidate	 = pSeries_lpar_hpte_invalidate;
@@ -600,6 +709,7 @@ void __init hpte_init_pseries(void)
 	mmu_hash_ops.flush_hash_range	 = pSeries_lpar_flush_hash_range;
 	mmu_hash_ops.hpte_clear_all      = pSeries_lpar_hptab_clear;
 	mmu_hash_ops.hugepage_invalidate = pSeries_lpar_hugepage_invalidate;
+	mmu_hash_ops.resize_hpt		 = pseries_lpar_resize_hpt;
 }
 
 #ifdef CONFIG_PPC_SMLPAR
-- 
2.9.3

Re: [PATCH 4/6] pseries: Add support for hash table resizing

[kbuild test robot]

[-- Attachment #1: Type: text/plain, Size: 1827 bytes --]

Hi David,

[auto build test ERROR on v4.9-rc8]
[cannot apply to powerpc/next kvm/linux-next kvm-ppc/kvm-ppc-next next-20161208]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/David-Gibson/powerpc-Hash-Page-Table-resizing-for-PAPR-guests/20161208-145142
config: powerpc-ps3_defconfig (attached as .config)
compiler: powerpc64-linux-gnu-gcc (Debian 6.1.1-9) 6.1.1 20160705
reproduce:
        wget https://git.kernel.org/cgit/linux/kernel/git/wfg/lkp-tests.git/plain/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        make.cross ARCH=powerpc 

All errors (new ones prefixed by >>):

   arch/powerpc/mm/hash_utils_64.c: In function 'hash64_debugfs':
>> arch/powerpc/mm/hash_utils_64.c:1838:45: error: 'powerpc_debugfs_root' undeclared (first use in this function)
     if (!debugfs_create_file("pft-size", 0600, powerpc_debugfs_root,
                                                ^~~~~~~~~~~~~~~~~~~~
   arch/powerpc/mm/hash_utils_64.c:1838:45: note: each undeclared identifier is reported only once for each function it appears in

vim +/powerpc_debugfs_root +1838 arch/powerpc/mm/hash_utils_64.c

  1832	
  1833	DEFINE_SIMPLE_ATTRIBUTE(fops_ppc64_pft_size,
  1834				ppc64_pft_size_get, ppc64_pft_size_set,	"%llu\n");
  1835	
  1836	static int __init hash64_debugfs(void)
  1837	{
> 1838		if (!debugfs_create_file("pft-size", 0600, powerpc_debugfs_root,
  1839					 NULL, &fops_ppc64_pft_size)) {
  1840			pr_err("lpar: unable to create ppc64_pft_size debugsfs file\n");
  1841		}

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

[-- Attachment #2: .config.gz --]
[-- Type: application/gzip, Size: 14177 bytes --]

[PATCH 5/6] pseries: Advertise HPT resizing support via CAS

[David Gibson]

The hypervisor needs to know a guest is capable of using the HPT resizing
PAPR extension in order to make full advantage of it for memory hotplug.

If the hypervisor knows the guest is HPT resize aware, it can size the
initial HPT based on the initial guest RAM size, relying on the guest to
resize the HPT when more memory is hot-added.  Without this, the hypervisor
must size the HPT for the maximum possible guest RAM, which can lead to
a huge waste of space if the guest never actually expends to that maximum
size.

This patch advertises the guest's support for HPT resizing via the
ibm,client-architecture-support OF interface.  We use bit 5 of byte 6 of
option vector 5 for this purpose (tentatively assigned in in-progress PAPR
change request).

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Anshuman Khandual <khandual@linux.vnet.ibm.com>
Reviewed-by: Paul Mackerras <paulus@samba.org>
---
 arch/powerpc/include/asm/prom.h | 1 +
 arch/powerpc/kernel/prom_init.c | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/include/asm/prom.h b/arch/powerpc/include/asm/prom.h
index 7f436ba..94c92bb 100644
--- a/arch/powerpc/include/asm/prom.h
+++ b/arch/powerpc/include/asm/prom.h
@@ -151,6 +151,7 @@ struct of_drconf_cell {
 #define OV5_XCMO		0x0440	/* Page Coalescing */
 #define OV5_TYPE1_AFFINITY	0x0580	/* Type 1 NUMA affinity */
 #define OV5_PRRN		0x0540	/* Platform Resource Reassignment */
+#define OV5_RESIZE_HPT		0x0601	/* Hash Page Table resizing */
 #define OV5_PFO_HW_RNG		0x0E80	/* PFO Random Number Generator */
 #define OV5_PFO_HW_842		0x0E40	/* PFO Compression Accelerator */
 #define OV5_PFO_HW_ENCR		0x0E20	/* PFO Encryption Accelerator */
diff --git a/arch/powerpc/kernel/prom_init.c b/arch/powerpc/kernel/prom_init.c
index 88ac964..9942d9f 100644
--- a/arch/powerpc/kernel/prom_init.c
+++ b/arch/powerpc/kernel/prom_init.c
@@ -713,7 +713,7 @@ unsigned char ibm_architecture_vec[] = {
 	0,
 #endif
 	OV5_FEAT(OV5_TYPE1_AFFINITY) | OV5_FEAT(OV5_PRRN),
-	0,
+	OV5_FEAT(OV5_RESIZE_HPT),
 	0,
 	0,
 	/* WARNING: The offset of the "number of cores" field below
-- 
2.9.3

[PATCH 6/6] pseries: Automatically resize HPT for memory hot add/remove

[David Gibson]

We've now implemented code in the pseries platform to use the new PAPR
interface to allow resizing the hash page table (HPT) at runtime.

This patch uses that interface to automatically attempt to resize the HPT
when memory is hot added or removed.  This tries to always keep the HPT at
a reasonable size for our current memory size.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Paul Mackerras <paulus@samba.org>
---
 arch/powerpc/include/asm/sparsemem.h |  1 +
 arch/powerpc/mm/hash_utils_64.c      | 29 +++++++++++++++++++++++++++++
 arch/powerpc/mm/mem.c                |  4 ++++
 3 files changed, 34 insertions(+)

diff --git a/arch/powerpc/include/asm/sparsemem.h b/arch/powerpc/include/asm/sparsemem.h
index f6fc0ee..737335c 100644
--- a/arch/powerpc/include/asm/sparsemem.h
+++ b/arch/powerpc/include/asm/sparsemem.h
@@ -16,6 +16,7 @@
 #endif /* CONFIG_SPARSEMEM */
 
 #ifdef CONFIG_MEMORY_HOTPLUG
+extern void resize_hpt_for_hotplug(unsigned long new_mem_size);
 extern int create_section_mapping(unsigned long start, unsigned long end);
 extern int remove_section_mapping(unsigned long start, unsigned long end);
 #ifdef CONFIG_NUMA
diff --git a/arch/powerpc/mm/hash_utils_64.c b/arch/powerpc/mm/hash_utils_64.c
index 474da2e..e2eb461 100644
--- a/arch/powerpc/mm/hash_utils_64.c
+++ b/arch/powerpc/mm/hash_utils_64.c
@@ -748,6 +748,35 @@ static unsigned long __init htab_get_table_size(void)
 }
 
 #ifdef CONFIG_MEMORY_HOTPLUG
+void resize_hpt_for_hotplug(unsigned long new_mem_size)
+{
+	unsigned target_hpt_shift;
+
+	if (!mmu_hash_ops.resize_hpt)
+		return;
+
+	target_hpt_shift = htab_shift_for_mem_size(new_mem_size);
+
+	/*
+	 * To avoid lots of HPT resizes if memory size is fluctuating
+	 * across a boundary, we deliberately have some hysterisis
+	 * here: we immediately increase the HPT size if the target
+	 * shift exceeds the current shift, but we won't attempt to
+	 * reduce unless the target shift is at least 2 below the
+	 * current shift
+	 */
+	if ((target_hpt_shift > ppc64_pft_size)
+	    || (target_hpt_shift < (ppc64_pft_size - 1))) {
+		int rc;
+
+		rc = mmu_hash_ops.resize_hpt(target_hpt_shift);
+		if (rc)
+			printk(KERN_WARNING
+			       "Unable to resize hash page table to target order %d: %d\n",
+			       target_hpt_shift, rc);
+	}
+}
+
 int create_section_mapping(unsigned long start, unsigned long end)
 {
 	int rc = htab_bolt_mapping(start, end, __pa(start),
diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
index 5f84433..9ee536e 100644
--- a/arch/powerpc/mm/mem.c
+++ b/arch/powerpc/mm/mem.c
@@ -134,6 +134,8 @@ int arch_add_memory(int nid, u64 start, u64 size, bool for_device)
 	unsigned long nr_pages = size >> PAGE_SHIFT;
 	int rc;
 
+	resize_hpt_for_hotplug(memblock_phys_mem_size());
+
 	pgdata = NODE_DATA(nid);
 
 	start = (unsigned long)__va(start);
@@ -174,6 +176,8 @@ int arch_remove_memory(u64 start, u64 size)
 	 */
 	vm_unmap_aliases();
 
+	resize_hpt_for_hotplug(memblock_phys_mem_size());
+
 	return ret;
 }
 #endif
-- 
2.9.3