linux-kernel - Re: [PATCH/RFC] module: replace module_layout with module

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Message-ID: <Y8gLJYA3ibA8De58@hirez.programming.kicks-ass.net>
Date:   Wed, 18 Jan 2023 16:07:17 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     Song Liu <song@...nel.org>,
        "linux-modules@...r.kernel.org" <linux-modules@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "songliubraving@...com" <songliubraving@...com>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH/RFC] module: replace module_layout with module_memory

On Tue, Jan 10, 2023 at 06:31:41AM +0000, Christophe Leroy wrote:
> Le 09/01/2023 à 21:51, Song Liu a écrit :

> > Do you mean one tree will cause addr_[min|max] to be inaccurate?
> > 
> 
> Yes at least. On powerpc you will have module text below kernel, 
> somewhere between 0xb0000000 and 0xcfffffff, and you will have module 
> data in vmalloc area, somewhere between 0xf0000000 and 0xffffffff.
> 
> If you have only one tree, any address between 0xc0000000 and 0xefffffff 
> will trigger a tree search.

The current min/max thing is tied to the tree because of easy update on
remove, but module-insert/remove is not a performance critical path.

So I think it should be possible to have {min,max}[TYPES] pairs.  Either
brute force the removal -- using a linear scan of the mod->list to find
the new bounds on removal.

Or overengineer the whole thing and use an augmented tree to keep that
many heaps in sync during the update -- but this seems total overkill.

The only consideration is testing that many ranges in
__module_address(), this is already 2 cachelines worth of range-checks
-- which seems a little excessive.

(also, I note that module_addr_{min,max} are unused these days)