Re: [PATCH] Reinstate "resource: avoid unnecessary lookups in find_next_iomem_res()"

[Andrew Morton]

On Mon, 24 Nov 2025 16:53:49 +0000 Ilias Stamatis <ilstam@xxxxxxxxxx> 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"?