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From:   "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
To:     Wei Xu <weixugc@google.com>
Cc:     "ying.huang@intel.com" <ying.huang@intel.com>,
        Andrew Morton <akpm@linux-foundation.org>,
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        Alistair Popple <apopple@nvidia.com>,
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        Linux MM <linux-mm@kvack.org>,
        Brice Goglin <brice.goglin@gmail.com>,
        Hesham Almatary <hesham.almatary@huawei.com>
Subject: Re: RFC: Memory Tiering Kernel Interfaces (v2)
In-Reply-To: <CAAPL-u-g86QqHaHGGtVJMER8ENC2dpekK+2qOkxoRFmC0F_80g@mail.gmail.com>
References: <CAAPL-u-DGLcKRVDnChN9ZhxPkfxQvz9Sb93kVoX_4J2oiJSkUw@mail.gmail.com>
 <56b41ce6922ed5f640d9bd46a603fa27576532a9.camel@intel.com>
 <c5d55131-76ff-7354-2954-7cfac365a9a5@linux.ibm.com>
 <CAAPL-u-g86QqHaHGGtVJMER8ENC2dpekK+2qOkxoRFmC0F_80g@mail.gmail.com>
Date:   Thu, 12 May 2022 13:06:10 +0530
Message-ID: <87y1z7jj85.fsf@linux.ibm.com>
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Wei Xu <weixugc@google.com> writes:

> On Thu, May 12, 2022 at 12:12 AM Aneesh Kumar K V
> <aneesh.kumar@linux.ibm.com> wrote:
>>
>> On 5/12/22 12:33 PM, ying.huang@intel.com wrote:
>> > On Wed, 2022-05-11 at 23:22 -0700, Wei Xu wrote:
>> >> Sysfs Interfaces
>> >> ================
>> >>
>> >> * /sys/devices/system/memtier/memtierN/nodelist
>> >>
>> >>    where N = 0, 1, 2 (the kernel supports only 3 tiers for now).
>> >>
>> >>    Format: node_list
>> >>
>> >>    Read-only.  When read, list the memory nodes in the specified tier.
>> >>
>> >>    Tier 0 is the highest tier, while tier 2 is the lowest tier.
>> >>
>> >>    The absolute value of a tier id number has no specific meaning.
>> >>    What matters is the relative order of the tier id numbers.
>> >>
>> >>    When a memory tier has no nodes, the kernel can hide its memtier
>> >>    sysfs files.
>> >>
>> >> * /sys/devices/system/node/nodeN/memtier
>> >>
>> >>    where N = 0, 1, ...
>> >>
>> >>    Format: int or empty
>> >>
>> >>    When read, list the memory tier that the node belongs to.  Its value
>> >>    is empty for a CPU-only NUMA node.
>> >>
>> >>    When written, the kernel moves the node into the specified memory
>> >>    tier if the move is allowed.  The tier assignment of all other nodes
>> >>    are not affected.
>> >>
>> >>    Initially, we can make this interface read-only.
>> >
>> > It seems that "/sys/devices/system/node/nodeN/memtier" has all
>> > information we needed.  Do we really need
>> > "/sys/devices/system/memtier/memtierN/nodelist"?
>> >
>> > That can be gotten via a simple shell command line,
>> >
>> > $ grep . /sys/devices/system/node/nodeN/memtier | sort -n -k 2 -t ':'
>> >
>>
>> It will be really useful to fetch the memory tier node list in an easy
>> fashion rather than reading multiple sysfs directories. If we don't have
>> other attributes for memorytier, we could keep
>> "/sys/devices/system/memtier/memtierN" a NUMA node list there by
>> avoiding /sys/devices/system/memtier/memtierN/nodelist
>>
>> -aneesh
>
> It is harder to implement memtierN as just a file and doesn't follow
> the existing sysfs pattern, either.  Besides, it is extensible to have
> memtierN as a directory. 

diff --git a/drivers/base/node.c b/drivers/base/node.c
index 6248326f944d..251f38ec3816 100644
--- a/drivers/base/node.c
+++ b/drivers/base/node.c
@@ -1097,12 +1097,49 @@ static struct attribute *node_state_attrs[] = {
 	NULL
 };
 
+#define MAX_TIER 3
+nodemask_t memory_tier[MAX_TIER];
+
+#define _TIER_ATTR_RO(name, tier_index)					\
+	{ __ATTR(name, 0444, show_tier, NULL), tier_index, NULL }
+
+struct memory_tier_attr {
+	struct device_attribute attr;
+	int tier_index;
+	int (*write)(nodemask_t nodes);
+};
+
+static ssize_t show_tier(struct device *dev,
+			 struct device_attribute *attr, char *buf)
+{
+	struct memory_tier_attr *mt = container_of(attr, struct memory_tier_attr, attr);
+
+	return sysfs_emit(buf, "%*pbl\n",
+			  nodemask_pr_args(&memory_tier[mt->tier_index]));
+}
+
 static const struct attribute_group memory_root_attr_group = {
 	.attrs = node_state_attrs,
 };
 
+
+#define TOP_TIER 0
+static struct memory_tier_attr memory_tiers[] = {
+	[0] = _TIER_ATTR_RO(memory_top_tier, TOP_TIER),
+};
+
+static struct attribute *memory_tier_attrs[] = {
+	&memory_tiers[0].attr.attr,
+	NULL
+};
+
+static const struct attribute_group memory_tier_attr_group = {
+	.attrs = memory_tier_attrs,
+};
+
 static const struct attribute_group *cpu_root_attr_groups[] = {
 	&memory_root_attr_group,
+	&memory_tier_attr_group,
 	NULL,
 };
 

As long as we have the ability to see the nodelist, I am good with the
proposal.

-aneesh