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Date: Mon, 18 Jul 2022 13:30:55 +0530
From: Aneesh Kumar K V <aneesh.kumar@...ux.ibm.com>
To: "Huang, Ying" <ying.huang@...el.com>
Cc: linux-mm@...ck.org, akpm@...ux-foundation.org,
Wei Xu <weixugc@...gle.com>, Yang Shi <shy828301@...il.com>,
Davidlohr Bueso <dave@...olabs.net>,
Tim C Chen <tim.c.chen@...el.com>,
Michal Hocko <mhocko@...nel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Hesham Almatary <hesham.almatary@...wei.com>,
Dave Hansen <dave.hansen@...el.com>,
Jonathan Cameron <Jonathan.Cameron@...wei.com>,
Alistair Popple <apopple@...dia.com>,
Dan Williams <dan.j.williams@...el.com>,
Johannes Weiner <hannes@...xchg.org>, jvgediya.oss@...il.com,
Jagdish Gediya <jvgediya@...ux.ibm.com>
Subject: Re: [PATCH v9 1/8] mm/demotion: Add support for explicit memory tiers
On 7/18/22 12:27 PM, Huang, Ying wrote:
> Aneesh Kumar K V <aneesh.kumar@...ux.ibm.com> writes:
>
>> On 7/15/22 1:23 PM, Huang, Ying wrote:
>
> [snip]
>
>>>
>>> You dropped the original sysfs interface patches from the series, but
>>> the kernel internal implementation is still for the original sysfs
>>> interface. For example, memory tier ID is for the original sysfs
>>> interface, not for the new proposed sysfs interface. So I suggest you
>>> to implement with the new interface in mind. What do you think about
>>> the following design?
>>>
>>
>> Sorry I am not able to follow you here. This patchset completely drops
>> exposing memory tiers to userspace via sysfs. Instead it allow
>> creation of memory tiers with specific tierID from within the kernel/device driver.
>> Default tierID is 200 and dax kmem creates memory tier with tierID 100.
>>
>>
>>> - Each NUMA node belongs to a memory type, and each memory type
>>> corresponds to a "abstract distance", so each NUMA node corresonds to
>>> a "distance". For simplicity, we can start with static distances, for
>>> example, DRAM (default): 150, PMEM: 250. The distance of each NUMA
>>> node can be recorded in a global array,
>>>
>>> int node_distances[MAX_NUMNODES];
>>>
>>> or, just
>>>
>>> pgdat->distance
>>>
>>
>> I don't follow this. I guess you are trying to have a different design.
>> Would it be much easier if you can write this in the form of a patch?
>
> Written some pseudo code as follow to show my basic idea.
>
> #define MEMORY_TIER_ADISTANCE_DRAM 150
> #define MEMORY_TIER_ADISTANCE_PMEM 250
>
> struct memory_tier {
> /* abstract distance range covered by the memory tier */
> int adistance_start;
> int adistance_len;
> struct list_head list;
> nodemask_t nodemask;
> };
>
> /* RCU list of memory tiers */
> static LIST_HEAD(memory_tiers);
>
> /* abstract distance of each NUMA node */
> int node_adistances[MAX_NUMNODES];
>
> struct memory_tier *find_create_memory_tier(int adistance)
> {
> struct memory_tier *tier;
>
> list_for_each_entry(tier, &memory_tiers, list) {
> if (adistance >= tier->adistance_start &&
> adistance < tier->adistance_start + tier->adistance_len)
> return tier;
> }
> /* allocate a new memory tier and return */
> }
>
> void memory_tier_add_node(int nid)
> {
> int adistance;
> struct memory_tier *tier;
>
> adistance = node_adistances[nid] || MEMORY_TIER_ADISTANCE_DRAM;
> tier = find_create_memory_tier(adistance);
> node_set(nid, &tier->nodemask);
> /* setup demotion data structure, etc */
> }
>
> static int __meminit migrate_on_reclaim_callback(struct notifier_block *self,
> unsigned long action, void *_arg)
> {
> struct memory_notify *arg = _arg;
> int nid;
>
> nid = arg->status_change_nid;
> if (nid < 0)
> return notifier_from_errno(0);
>
> switch (action) {
> case MEM_ONLINE:
> memory_tier_add_node(nid);
> break;
> }
>
> return notifier_from_errno(0);
> }
>
> /* kmem.c */
> static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
> {
> node_adistances[dev_dax->target_node] = MEMORY_TIER_ADISTANCE_PMEM;
> /* add_memory_driver_managed() */
> }
>
> [snip]
>
> Best Regards,
> Huang, Ying
Implementing that I ended up with the below. The difference is adistance_len is not a memory tier property
instead it is a kernel parameter like memory_tier_chunk_size which can be tuned to create more memory tiers.
How about this? Not yet tested.
struct memory_tier {
struct list_head list;
int id;
int perf_level;
nodemask_t nodelist;
};
static LIST_HEAD(memory_tiers);
static DEFINE_MUTEX(memory_tier_lock);
static unsigned int default_memtier_perf_level = DEFAULT_MEMORY_TYPE_PERF;
core_param(default_memory_tier_perf_level, default_memtier_perf_level, uint, 0644);
static unsigned int memtier_perf_chunk_size = 150;
core_param(memory_tier_perf_chunk, memtier_perf_chunk_size, uint, 0644);
/*
* performance levels are grouped into memtiers each of chunk size
* memtier_perf_chunk
*/
static struct memory_tier *find_create_memory_tier(unsigned int perf_level)
{
bool found_slot = false;
struct list_head *ent;
struct memory_tier *memtier, *new_memtier;
static int next_memtier_id = 0;
/*
* zero is special in that it indicates uninitialized
* perf level by respective driver. Pick default memory
* tier perf level for that.
*/
if (!perf_level)
perf_level = default_memtier_perf_level;
lockdep_assert_held_once(&memory_tier_lock);
list_for_each(ent, &memory_tiers) {
memtier = list_entry(ent, struct memory_tier, list);
if (perf_level >= memtier->perf_level &&
perf_level < memtier->perf_level + memtier_perf_chunk_size)
return memtier;
else if (perf_level < memtier->perf_level) {
found_slot = true;
break;
}
}
new_memtier = kzalloc(sizeof(struct memory_tier), GFP_KERNEL);
if (!new_memtier)
return ERR_PTR(-ENOMEM);
new_memtier->id = next_memtier_id++;
new_memtier->perf_level = ALIGN_DOWN(perf_level, memtier_perf_chunk_size);
if (found_slot)
list_add_tail(&new_memtier->list, ent);
else
list_add_tail(&new_memtier->list, &memory_tiers);
return new_memtier;
}
static int __init memory_tier_init(void)
{
int node;
struct memory_tier *memtier;
/*
* Since this is early during boot, we could avoid
* holding memtory_tier_lock. But keep it simple by
* holding locks. So we can add lock held debug checks
* in other functions.
*/
mutex_lock(&memory_tier_lock);
memtier = find_create_memory_tier(default_memtier_perf_level);
if (IS_ERR(memtier))
panic("%s() failed to register memory tier: %ld\n",
__func__, PTR_ERR(memtier));
/* CPU only nodes are not part of memory tiers. */
memtier->nodelist = node_states[N_MEMORY];
/*
* nodes that are already online and that doesn't
* have perf level assigned is assigned a default perf
* level.
*/
for_each_node_state(node, N_MEMORY) {
struct node *node_property = node_devices[node];
if (!node_property->perf_level)
node_property->perf_level = default_memtier_perf_level;
}
mutex_unlock(&memory_tier_lock);
return 0;
}
subsys_initcall(memory_tier_init);
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