linux-kernel - Re: [PATCH 00/21] mm: ASI direct map management

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Message-ID: <DD7SCRK2OJI9.1EJ9GSEH9FHW2@google.com>
Date: Thu, 02 Oct 2025 11:05:20 +0000
From: Brendan Jackman <jackmanb@...gle.com>
To: Dave Hansen <dave.hansen@...el.com>, Yosry Ahmed <yosry.ahmed@...ux.dev>
Cc: Brendan Jackman <jackmanb@...gle.com>, Andy Lutomirski <luto@...nel.org>, 
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, "Liam R. Howlett" <Liam.Howlett@...cle.com>, 
	Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>, 
	Johannes Weiner <hannes@...xchg.org>, Zi Yan <ziy@...dia.com>, 
	Axel Rasmussen <axelrasmussen@...gle.com>, Yuanchu Xie <yuanchu@...gle.com>, 
	Roman Gushchin <roman.gushchin@...ux.dev>, <peterz@...radead.org>, <bp@...en8.de>, 
	<dave.hansen@...ux.intel.com>, <mingo@...hat.com>, <tglx@...utronix.de>, 
	<akpm@...ux-foundation.org>, <david@...hat.com>, <derkling@...gle.com>, 
	<junaids@...gle.com>, <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>, 
	<reijiw@...gle.com>, <rientjes@...gle.com>, <rppt@...nel.org>, 
	<vbabka@...e.cz>, <x86@...nel.org>
Subject: Re: [PATCH 00/21] mm: ASI direct map management

On Wed Oct 1, 2025 at 8:30 PM UTC, Dave Hansen wrote:
> On 10/1/25 13:22, Yosry Ahmed wrote:
>> On Wed, Oct 01, 2025 at 12:54:42PM -0700, Dave Hansen wrote:
>>> On 9/24/25 07:59, Brendan Jackman wrote:
>>>> As per [0] I think ASI is ready to start merging. This is the first
>>>> step. The scope of this series is: everything needed to set up the
>>>> direct map in the restricted address spaces.
>>> Brendan!
>>>
>>> Generally, we ask that patches get review tags before we consider them
>>> for being merged. Is there a reason this series doesn't need reviews
>>> before it gets merged?
>> I think Brendan just meant that this is not an RFC aimed at prompting
>> discussion anymore, these are fully functional patches aimed at being
>> merged after they are reviewed and iterated on accordingly.
>
> Just setting expectations ... I think Brendan has probably rewritten
> this two or three times. I suggest he's about halfway done; only two or
> three rewrites left. ;)

Yeah, I'd love to say "... and we have become exceedingly efficient at
it" [0], but no, debugging my idiotic freelist and pagetable corruptions
was just as hard this time as the first and second times...

[0] https://www.youtube.com/watch?v=r51EomcIqA0

> But, seriously, this _is_ a big deal. It's not going to be something
> that gets a few tags slapped on it and gets merged. At least that's not
> how I expect it to go.

Yeah, sorry if this was poorly worded, I'm DEFINITELY not asking anyone
to merge this without the requisite acks - "ready for merge" just means
"please review this as real grown-up code, I no longer consider this a
PoC". And I'm not expecting this to get merged in v2 either :)

Maybe worth noting here: there are two broad parties of important
reviewers - mm folks and x86 folks. I think we're at risk of a
chicken-and-egg problem where party A is thinking "no point in reviewing
this too carefully, it's not yet clear that party B is ever gonna accept
ASI even in theory". Meanwhile party B says "yeah ASI seems desirable,
but I'll keep my nose out until party A has ironed out the details on
their side".

So, if you can do anything to help develop a consensus on whether we
actually want this thing, that would help a lot. Maybe the best way to
do that is just to dig into the details anyway, I'm not sure.