Re: [LSF/MM/BPF TOPIC] DAMON Requirements for Access-aware MM of Future

[Yuanchu Xie <yuanchu@google.com>]

On Mon, Jan 13, 2025 at 7:06 PM Gregory Price <gourry@gourry.net> wrote:
> 5) Scarce resources
>
>    We need to be careful not to consume excessive amounts of resources
>    in an attempt to track all these identifying mechanisms.  Even 1 byte
>    per folio is 256MB on a 1TB machine.  This gets out of hand quick.
>
>    With task-work, I was able to add no additional resource consumption,
>    but deferring to a fully async scenario and needing to track things
>    like last-accessing CPU, timestamps, and etc.
>
>    We'll need to examine this closely if we decide to aggregate either
>    of these mechanisms.
My concern with physical address space monitoring is fragmentation. I
ran some numbers on a few prod machines. Grouping by regions with the
same memcg and ignoring any unmapped memory to be generous, machines
with higher utilization can have a region/total pages ratio of ~40%,
and even those with lower utilization (<50%) can also reach 20%.
Accurately tracking these regions would require quite the region
metadata, on the order of GBs.