linux-kernel - Re: [PATCH] x86/mce: Increase the size of the MCE pool from 2 to 8 pages

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Message-ID: <dd72296c-def6-4fb3-9984-348641cdb6a4@intel.com>
Date:   Mon, 16 Oct 2023 07:24:34 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Yazen Ghannam <yazen.ghannam@....com>,
        "Sironi, Filippo" <sironi@...zon.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc:     "tony.luck@...el.com" <tony.luck@...el.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "x86@...nel.org" <x86@...nel.org>, "hpa@...or.com" <hpa@...or.com>,
        "linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>
Subject: Re: [PATCH] x86/mce: Increase the size of the MCE pool from 2 to 8
 pages

On 10/16/23 07:14, Yazen Ghannam wrote:
> 1) Keep the current config size for boot time. 
> 2) Add a kernel parameter
> and/or sysfs file to allow users to request additional genpool capacity.
> 3) Use gen_pool_add(), or whichever, to add the capacity based on user
> input. Maybe this can be expanded later to be automatic. But I think it
> simpler to start with explicit user input.

I guarantee virtually nobody will ever use an explicit kernel interface
to bump the size up.  It'll be the same exact folks that recompile their
kernels.

An automatic resizing one doesn't have to be fancy and only has to
expand once:

static bool expanded = false;

...

	if (full && !expanded) {
		expand();
		expanded = true;
	}

It might be a _wee_ bit worse than that because you might have to queue
some work outside of #MC context but seriously we're talking 10-ish
lines of code.  It'd probably be even smaller than doing it when poked
by userspace and wouldn't involve new ABI.