Re: [PATCH v2] mm/mempolicy: track page allocations per mempolicy

["Huang, Ying" <ying.huang@linux.alibaba.com>]

"JP Kobryn (Meta)" <jp.kobryn@linux.dev> writes:

> On 3/12/26 6:40 AM, Vlastimil Babka (SUSE) wrote:
>> On 3/7/26 05:55, JP Kobryn (Meta) wrote:
>>> When investigating pressure on a NUMA node, there is no straightforward way
>>> to determine which policies are driving allocations to it.
>>>
>>> Add per-policy page allocation counters as new node stat items. These
>>> counters track allocations to nodes and also whether the allocations were
>>> intentional or fallbacks.
>>>
>>> The new stats follow the existing numa hit/miss/foreign style and have the
>>> following meanings:
>>>
>>>    hit
>>>      - for BIND and PREFERRED_MANY, allocation succeeded on node in nodemask
>>>      - for other policies, allocation succeeded on intended node
>>>      - counted on the node of the allocation
>>>    miss
>>>      - allocation intended for other node, but happened on this one
>>>      - counted on other node
>>>    foreign
>>>      - allocation intended on this node, but happened on other node
>>>      - counted on this node
>>>
>>> Counters are exposed per-memcg, per-node in memory.numa_stat and globally
>>> in /proc/vmstat.
>>>
>>> Signed-off-by: JP Kobryn (Meta) <jp.kobryn@linux.dev>
>> I think I've been on of the folks on previous versions arguing
>> against the
>> many counters, and one of the arguments was it they can't tell the full
>> story anyway (compared to e.g. tracing), but I don't think adding even more
>> counters is the right solution. Seems like a number of other people
>> responding to the thread are providing similar feedback.
>> For example I'm still not sure how it would help me if I knew the
>> hits/misses were due to a preferred vs preferred_many policy, or interleave
>> vs weithed interleave?
>> 
>
> How about I change from per-policy hit/miss/foreign triplets to a single
> aggregated policy triplet (i.e. just 3 new counters which account for
> all policies)? They would follow the same hit/miss/foreign semantics
> already proposed (visible in quoted text above). This would still
> provide the otherwise missing signal of whether policy-driven
> allocations to a node are intentional or fallback.
>
> Note that I am also planning on moving the stats off of the memcg so the
> 3 new counters will be global per-node in response to similar feedback.

Emm, what's the difference between these newly added counters and the
existing numa_hit/miss/foreign counters?

---
Best Regards,
Huang, Ying