As per PAPR, there are 2 device tree property
ibm,max-associativity-domains (which defines the maximum number of
domains that the firmware i.e PowerVM can support) and
ibm,current-associativity-domains (which defines the maximum number of
domains that the platform can support). Value of
ibm,max-associativity-domains property is always greater than or equal
to ibm,current-associativity-domains property.
Powerpc currently uses ibm,max-associativity-domains property while
setting the possible number of nodes. This is currently set at 32.
However the possible number of nodes for a platform may be significantly
less. Hence set the possible number of nodes based on
ibm,current-associativity-domains property.
$ lsprop /proc/device-tree/rtas/ibm,*associ*-domains
/proc/device-tree/rtas/ibm,current-associativity-domains
00000005 00000001 00000002 00000002 00000002 00000010
/proc/device-tree/rtas/ibm,max-associativity-domains
00000005 00000001 00000008 00000020 00000020 00000100
$ cat /sys/devices/system/node/possible ##Before patch
0-31
$ cat /sys/devices/system/node/possible ##After patch
0-1
Note the maximum nodes this platform can support is only 2 but the
possible nodes is set to 32.
This is important because lot of kernel and user space code allocate
structures for all possible nodes leading to a lot of memory that is
allocated but not used.
I ran a simple experiment to create and destroy 100 memory cgroups on
boot on a 8 node machine (Power8 Alpine).
Before patch
free -k at boot
total used free shared buff/cache available
Mem: 523498176 4106816 518820608 22272 570752 516606720
Swap: 4194240 0 4194240
free -k after creating 100 memory cgroups
total used free shared buff/cache available
Mem: 523498176 4628416 518246464 22336 623296 516058688
Swap: 4194240 0 4194240
free -k after destroying 100 memory cgroups
total used free shared buff/cache available
Mem: 523498176 4697408 518173760 22400 627008 515987904
Swap: 4194240 0 4194240
After patch
free -k at boot
total used free shared buff/cache available
Mem: 523498176 3969472 518933888 22272 594816 516731776
Swap: 4194240 0 4194240
free -k after creating 100 memory cgroups
total used free shared buff/cache available
Mem: 523498176 4181888 518676096 22208 640192 516496448
Swap: 4194240 0 4194240
free -k after destroying 100 memory cgroups
total used free shared buff/cache available
Mem: 523498176 4232320 518619904 22272 645952 516443264
Swap: 4194240 0 4194240
Observations:
Fixed kernel takes 137344 kb (4106816-3969472) less to boot.
Fixed kernel takes 309184 kb (4628416-4181888-137344) less to create 100 memcgs.
Cc: Nathan Lynch <nath...@linux.ibm.com>
Cc: Michael Ellerman <m...@ellerman.id.au>
Cc: linuxppc-dev@lists.ozlabs.org
Cc: Anton Blanchard <an...@ozlabs.org>
Cc: Bharata B Rao <bhar...@linux.ibm.com>
Cc: Tyrel Datwyler <tyr...@linux.ibm.com>
Signed-off-by: Srikar Dronamraju <sri...@linux.vnet.ibm.com>
---
v1:
https://lore.kernel.org/linuxppc-dev/20200706064002.14848-1-sri...@linux.vnet.ibm.com/t/#u
Changelog v1->v2:
Fallback to ibm,max-associativity-domains if ibm,current-associativity
is not available. Suggested by Tyrel Datwyler.
arch/powerpc/mm/numa.c | 15 ++++++++++++---
1 file changed, 12 insertions(+), 3 deletions(-)
diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
index 9fcf2d195830..fc7b0505bdd8 100644
--- a/arch/powerpc/mm/numa.c
+++ b/arch/powerpc/mm/numa.c
@@ -896,10 +896,19 @@ static void __init find_possible_nodes(void)
if (!rtas)
return;
- if (of_property_read_u32_index(rtas,
- "ibm,max-associativity-domains",
+ if (of_property_read_u32_index(rtas,
"ibm,current-associativity-domains",
+ min_common_depth, &numnodes)) {
+ /*
+ * ibm,current-associativity-domains is a fairly recent
+ * property. If it doesn't exist, then fallback on
+ * ibm,max-associativity-domains. Current denotes what the
+ * platform can support compared to max which denotes what the
+ * Hypervisor can support.
+ */
+ if (of_property_read_u32_index(rtas,
"ibm,max-associativity-domains",
min_common_depth, &numnodes))
- goto out;
+ goto out;
+ }
for (i = 0; i < numnodes; i++) {
if (!node_possible(i))
--
2.18.2
