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

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Date: Wed, 27 Mar 2024 09:52:07 +0100
From: David Hildenbrand <david@...hat.com>
To: Vishal Moola <vishal.moola@...il.com>,
 Qi Zheng <zhengqi.arch@...edance.com>
Cc: akpm@...ux-foundation.org, hughd@...gle.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 26.03.24 20:07, Vishal Moola wrote:
> 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.

The gmap shadow pages are page tables that are not linked into the user 
page tables.

I recall I raised in the past that using ptdesc from them is confusing.

-- 
Cheers,

David / dhildenb