linux-kernel - Re: [RFC PATCH v2 0/8] mm: Hot page tracking and promotion infrastructure

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Message-ID: <20251022100950.00002785@huawei.com>
Date: Wed, 22 Oct 2025 10:09:50 +0100
From: Jonathan Cameron <jonathan.cameron@...wei.com>
To: Gregory Price <gourry@...rry.net>, <hannes@...xchg.org>
CC: Yiannis Nikolakopoulos <yiannis.nikolakop@...il.com>, Wei Xu
	<weixugc@...gle.com>, David Rientjes <rientjes@...gle.com>, Matthew Wilcox
	<willy@...radead.org>, Bharata B Rao <bharata@....com>,
	<linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
	<dave.hansen@...el.com>, <mgorman@...hsingularity.net>, <mingo@...hat.com>,
	<peterz@...radead.org>, <raghavendra.kt@....com>, <riel@...riel.com>,
	<sj@...nel.org>, <ying.huang@...ux.alibaba.com>, <ziy@...dia.com>,
	<dave@...olabs.net>, <nifan.cxl@...il.com>, <xuezhengchu@...wei.com>,
	<akpm@...ux-foundation.org>, <david@...hat.com>, <byungchul@...com>,
	<kinseyho@...gle.com>, <joshua.hahnjy@...il.com>, <yuanchu@...gle.com>,
	<balbirs@...dia.com>, <alok.rathore@...sung.com>, <yiannis@...corp.com>, Adam
 Manzanares <a.manzanares@...sung.com>
Subject: Re: [RFC PATCH v2 0/8] mm: Hot page tracking and promotion
 infrastructure

On Tue, 21 Oct 2025 14:57:26 -0400
Gregory Price <gourry@...rry.net> wrote:

> On Tue, Oct 21, 2025 at 02:52:40PM -0400, Gregory Price wrote:
> > I would prefer the former, since this is already what's done for
> > hostbridge interleave vs non-interleave setups, where the host may
> > expose multiple CFMW for the same devices depending on how the OS.  
> 
> bah, got distracted
> 
> "Depending on how the OS may choose to configure things at some unknown
> point in the future"

My gut feeling is the need to do dynamic NUMA nodes will not be driven
but this but more by large scale fabrics (if that ever happens)
and trade offs of host PA space vs QoS in the hardware.  Those
trade offs might put memory with very different performance
characteristics behind one window.

Maybe it'll become a thing that can be used for compression.
Otherwise compression from host hardware point of view might be
like the question of share or separate fixed memory windows for
persistent / volatile. Ideally they'd be separate but if Host PA space
is limited, someone might build a system where a single fixed memory
window is used to support both.

Possible virtualization of some of this stuff will make it more complex
again.  Any crazy mess can share a fake fixed memory window as the QoS is
all behind some page tables.

Meh. Let's suggest people burn host PA space for now.  If anyone hits
that limit they can solve it (crosses fingers it's not my lot :)

Jonathan

> 
> 
> ~Gregory