linux-kernel - Re: [PATCH 0/3] minor fixes and supplement for ptdesc

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Date: Tue, 26 Mar 2024 12:07:41 -0700
From: Vishal Moola <vishal.moola@...il.com>
To: Qi Zheng <zhengqi.arch@...edance.com>
Cc: akpm@...ux-foundation.org, hughd@...gle.com, david@...hat.com,
	rppt@...nel.org, willy@...radead.org, muchun.song@...ux.dev,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] minor fixes and supplement for ptdesc

On Mon, Mar 04, 2024 at 07:07:17PM +0800, Qi Zheng wrote:
> Hi all,

Sorry for the late review. Thanks for looking at doing some ptdesc
conversions. This patchset has the right idea and looks *mostly* fine.

> In this series, the [PATCH 1/3] and [PATCH 2/3] are fixes for some issues
> discovered during code inspection.
> 
> The [PATCH 3/3] is a supplement to ptdesc conversion in s390, I don't know
> why this is not done in the commit 6326c26c1514 ("s390: convert various pgalloc
> functions to use ptdescs"), maybe I missed something. And since I don't have an

It's important to keep in mind the end goal of ptdescs, cleaning up much
of the struct page field misuse by standardizing their usage. s390 page
tables and gmap are similar but not the same, so the conversions require
deeper thought. 

My initial "Split ptdesc from struct page" patchset tried to focus on the
most straightforward, simple conversions in order to introduce the
descriptor and lay a foundation for future conversions - you can see some
more complicated iterations v6 and prior.

When converting to ptdescs (and any other newer descriptors), we should
be careful about generating superficial code churn instead of using
them to solve the problems they are trying to solve.