linux-kernel - Re: [RFC PATCH v4 0/6] Promotion of Unmapped Page Cache Folios.

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Message-ID: <Z_uymiNhC6doPD23@casper.infradead.org>
Date: Sun, 13 Apr 2025 13:48:26 +0100
From: Matthew Wilcox <willy@...radead.org>
To: Donet Tom <donettom@...ux.ibm.com>
Cc: Gregory Price <gourry@...rry.net>, linux-mm@...ck.org,
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
	kernel-team@...a.com, akpm@...ux-foundation.org, mingo@...hat.com,
	peterz@...radead.org, juri.lelli@...hat.com,
	vincent.guittot@...aro.org, hannes@...xchg.org, mhocko@...nel.org,
	roman.gushchin@...ux.dev, shakeel.butt@...ux.dev,
	Huang Ying <ying.huang@...ux.alibaba.com>,
	Keith Busch <kbusch@...a.com>, Feng Tang <feng.tang@...el.com>,
	Neha Gholkar <nehagholkar@...a.com>
Subject: Re: [RFC PATCH v4 0/6] Promotion of Unmapped Page Cache Folios.

On Sun, Apr 13, 2025 at 10:53:48AM +0530, Donet Tom wrote:
> 
> On 4/12/25 5:19 AM, Matthew Wilcox wrote:
> > On Fri, Apr 11, 2025 at 06:11:05PM -0400, Gregory Price wrote:
> > > Unmapped page cache pages can be demoted to low-tier memory, but
> > No.  Page cache should never be demoted to low-tier memory.
> > NACK this patchset.
> 
> Hi Mathew,
> 
> I have one doubt. Under memory pressure, page cache allocations can
> fall back to lower-tier memory, right? So later, if those page cache pages
> become hot, shouldn't we promote them?

That shouldn't happen either.  CXL should never be added to the page
allocator.  You guys are creating a lot of problems for yourselves,
and I've been clear that I want no part of this.
>