linux-kernel - Re: [PATCH v17 08/26] x86/mm: Introduce _PAGE

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Date:   Thu, 21 Jan 2021 12:44:38 -0800
From:   "Yu, Yu-cheng" <yu-cheng.yu@...el.com>
To:     Dave Hansen <dave.hansen@...el.com>, Borislav Petkov <bp@...en8.de>
Cc:     x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...nel.org>,
        Balbir Singh <bsingharora@...il.com>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        Florian Weimer <fweimer@...hat.com>,
        "H.J. Lu" <hjl.tools@...il.com>, Jann Horn <jannh@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Oleg Nesterov <oleg@...hat.com>, Pavel Machek <pavel@....cz>,
        Peter Zijlstra <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@...el.com>,
        Dave Martin <Dave.Martin@....com>,
        Weijiang Yang <weijiang.yang@...el.com>,
        Pengfei Xu <pengfei.xu@...el.com>
Subject: Re: [PATCH v17 08/26] x86/mm: Introduce _PAGE_COW

On 1/21/2021 12:26 PM, Dave Hansen wrote:
>> Usually, the compiler is better at making code efficient than humans.  I
>> find that coding it in the most human-readable way is best unless I
>> *know* the compiler is unable to generate god code.
> 
> "good code", even.
> 
> I really want a "god code" compiler, though. :)
> 
With my version of GCC, the shifting implementation creates five 
instructions, all operate on registers only.  The other implementation 
also creates five instructions, but introduces one jump and one memory 
access.  But, you are right, being readable is also important.  Maybe we 
can tweak it a little or create something similar to those in bitops.

--
Yu-cheng