linux-kernel - Re: [PATCH 02/16] mm: introduce leaf entry type and use to simplify leaf entry logic

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Message-ID: <7f507cb7-f6aa-4f52-b0b5-8f0f27905122@gmail.com>
Date: Wed, 5 Nov 2025 21:11:45 +0100
From: "David Hildenbrand (Red Hat)" <davidhildenbrandkernel@...il.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Gregory Price <gourry@...rry.net>
Cc: Matthew Wilcox <willy@...radead.org>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Christian Borntraeger <borntraeger@...ux.ibm.com>,
 Janosch Frank <frankja@...ux.ibm.com>,
 Claudio Imbrenda <imbrenda@...ux.ibm.com>,
 Alexander Gordeev <agordeev@...ux.ibm.com>,
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 Alexander Viro <viro@...iv.linux.org.uk>,
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 Arnd Bergmann <arnd@...db.de>, Zi Yan <ziy@...dia.com>,
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Subject: Re: [PATCH 02/16] mm: introduce leaf entry type and use to simplify
 leaf entry logic

On 05.11.25 21:05, Lorenzo Stoakes wrote:
> On Wed, Nov 05, 2025 at 03:01:00PM -0500, Gregory Price wrote:
>> On Wed, Nov 05, 2025 at 07:52:36PM +0000, Lorenzo Stoakes wrote:
>>> On Wed, Nov 05, 2025 at 02:25:34PM -0500, Gregory Price wrote:
>>>> On Wed, Nov 05, 2025 at 07:06:11PM +0000, Matthew Wilcox wrote:
>>> I thought about doing this but it doesn't really work as the type is
>>> _abstracted_ from the architecture-specific value, _and_ we use what is
>>> currently the swp_type field to identify what this is.
>>>
>>> So we would lose the architecture-specific information that any 'hardware leaf'
>>> entry would require and not be able to reliably identify it without losing bits.
>>>
>>> Trying to preserve the value _and_ correctly identify it as a present entry
>>> would be difficult.
>>>
>>> And I _really_ didn't want to go on a deep dive through all the architectures to
>>> see if we could encode it differently to allow for this.
>>>
>>> Rather I think it's better to differentiate between s/w + h/w leaf entries.
>>>
>>
>> Reasonable - names are hard, but just about anything will be better than swp_entry.
>>
>> SWE / sw_entry seems perfectly reasonable.
> 
> I'm not a lover of 'sw' in there it's just... eye-stabby. Is that a word?
> 
> I am quite fond of my suggested soft_leaf_t, softleaf_xxx()

We do have soft_dirty.

It will get interesting with pte_swp_soft_dirty() :)

ptw_softlead_soft_dirty() Well, at least I would understand it.