Re: [RFC] Memory tiering kernel alignment

[SeongJae Park <sj@kernel.org>]

On Thu, 25 Jan 2024 13:37:02 -0800 (PST) David Rientjes <rientjes@google.com> wrote:

> 
> On Thu, 25 Jan 2024, Matthew Wilcox wrote:
> 
> > On Thu, Jan 25, 2024 at 12:04:37PM -0800, David Rientjes wrote:
> > > On Thu, 25 Jan 2024, Matthew Wilcox wrote:
> > > > On Thu, Jan 25, 2024 at 10:26:19AM -0800, David Rientjes wrote:
[...]
> This is **exactly** the type of discussion we're looking to have :)
> 
> There are some things that I've chatted informally with folks about that 
> I'd like to bring to the forum:
> 
>  - Decoupling CPU migration from memory migration for NUMA Balancing (or
>    perhaps deprecating CPU migration entirely)
> 
>  - Allowing NUMA Balancing to do migration as part of a kthread 
>    asynchronous to the NUMA hint fault, in kernel context
> 
>  - Abstraction for future hardware devices that can provide an expanded
>    view into page hotness that can be leveraged in different areas of the
>    kernel, including as a backend for NUMA Balanacing to replace NUMA
>    hint faults
> 
>  - Per-container support for configuring balancing and memory migration
> 
>  - Opting certain types of memory into NUMA Balancing (like tmpfs) while
>    leaving other types alone
> 
>  - Utilizing hardware accelerated memory migration as a replacement for
>    the traditional migrate_pages() path when available
> 
> I could go code all of this up and spend an enormous amount of time doing 
> so only to get NAKed by somebody because I'm ripping out their critical 
> use case that I just didn't know about :)  There's also the question of 
> whether DAMON should be the source of truth for this or it should be 
> decoupled.

I wouldn't dare to say DAMON should be the source of truth, but I hope DAMON to
be somewhat useful.  DAMON is designed to be able to be easily extended[1] for
various access monitoring / memory management primitives including hardware
features.  DAMOS of today provides a feature called filter[2], which allows
applying specific operations to specific pages depending on their
non-access-pattern information including type (anon vs file-backed) and which
memcg it belongs to.  Hence I think DAMON might be able to be used for a few of
above cases.

[1] https://docs.kernel.org/mm/damon/design.html#configurable-operations-set
[2] https://docs.kernel.org/mm/damon/design.html#filters


Thanks,
SJ

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