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

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Message-Id: <20251124085816.07dbf5a4ec6235b2943840a0@linux-foundation.org>
Date: Mon, 24 Nov 2025 08:58:16 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Ilias Stamatis <ilstam@...zon.com>
Cc: <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
 <david@...nel.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 Mon, 24 Nov 2025 16:53:49 +0000 Ilias Stamatis <ilstam@...zon.com> 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.
> 
> As the original commit message of the optimization explains there is no
> point considering the children of a subtree in find_next_iomem_res() if
> the top level range does not match. Reinstating the optimization results
> in significant performance improvements in systems with very large iomem
> maps when mmaping /dev/mem.

It would be great if we could quantify "significant performance
improvements"?