linux-kernel - Re: [PATCH 1/2] x86/mm: Kill a 32-bit #ifdef for shared PMD handling

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Message-ID: <a2f144f8-09ae-449a-a005-bc8d76dd0260@intel.com>
Date: Fri, 18 Apr 2025 11:49:12 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>
Cc: "luto@...nel.org" <luto@...nel.org>, "jgross@...e.com" <jgross@...e.com>,
 "x86@...nel.org" <x86@...nel.org>, "joro@...tes.org" <joro@...tes.org>,
 "peterz@...radead.org" <peterz@...radead.org>, "bp@...en8.de"
 <bp@...en8.de>, "tglx@...utronix.de" <tglx@...utronix.de>,
 "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH 1/2] x86/mm: Kill a 32-bit #ifdef for shared PMD handling

On 4/18/25 11:18, Edgecombe, Rick P wrote:
> On Fri, 2025-04-18 at 08:56 -0700, Dave Hansen wrote:
>> +
>> +	if (IS_ENABLED(CONFIG_X86_64))
>> +		return;
> Nit to throw away if you don't like it, but the below code the conditional is
> about special 32 bit requirements, not, not being 64 bit. So I'd have done:
> 
> 	if (!IS_ENABLED(CONFIG_X86_32))
> 		return;
> 
> Probably anyone reading this is going to know CONFIG_X86_64 and CONFIG_X86_32
> are exclusive, and there are only two options. But to me the check is a tiny bit
> harder to read this way. In either case:

I like the suggestion. I think I even wrote it that way originally.

I eventually decided to try and optimize for the lucky guy who comes
through some day and is removing all the non-64-bit code. It would be
easier for them to intuit that the cruft can go away here:

	if (IS_ENABLED(CONFIG_X86_64))
		return;
	// cruft

Does that make sense, or am I optimizing for the wrong thing?