linux-kernel - Re: [PATCH] Reinstate "resource: avoid unnecessary lookups in find_next_iomem

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Message-ID: <9fdc1d1f-ce00-47ff-bdf5-66e8a511be25@kernel.org>
Date: Tue, 25 Nov 2025 09:09:02 +0100
From: "David Hildenbrand (Red Hat)" <david@...nel.org>
To: Ilias Stamatis <ilstam@...zon.com>, akpm@...ux-foundation.org,
 linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org, nadav.amit@...il.com, huang.ying.caritas@...il.com,
 andriy.shevchenko@...ux.intel.com, bhe@...hat.com, nh-open-source@...zon.com
Subject: Re: [PATCH] Reinstate "resource: avoid unnecessary lookups in
 find_next_iomem_res()"

On 11/24/25 17:53, Ilias Stamatis wrote:
> Commit 97523a4edb7b ("kernel/resource: remove first_lvl / siblings_only
> logic") removed an optimization introduced by commit 756398750e11
> ("resource: avoid unnecessary lookups in find_next_iomem_res()"). That
> was not called out in the message of the first commit explicitly so it's
> not entirely clear whether removing the optimization happened
> inadvertently or not.

Remembering the history, we have some things where the top might not
fully describe what the lower levels do.

An example is for example found here:

Author: Dan Williams <dan.j.williams@...el.com>
Date:   Thu Feb 16 00:36:02 2023 -0800

     dax/kmem: Fix leak of memory-hotplug resources
     
     While experimenting with CXL region removal the following corruption of
     /proc/iomem appeared.
     
     Before:
     f010000000-f04fffffff : CXL Window 0
       f010000000-f02fffffff : region4
         f010000000-f02fffffff : dax4.0
           f010000000-f02fffffff : System RAM (kmem)

The CXL Windows will certainly not match System RAM, as one example.

How would your change affect such cases?


-- 
Cheers

David