linux-kernel - Re: [RFC PATCH 34/56] x86/alternative: Save old bytes for alternatives

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Message-ID: <2ae957fc-b686-4662-9e10-6dca1f10c749@suse.com>
Date: Thu, 30 Oct 2025 17:42:59 +0200
From: Nikolay Borisov <nik.borisov@...e.com>
To: "Kaplan, David" <David.Kaplan@....com>,
 David Laight <david.laight.linux@...il.com>
Cc: Juergen Gross <jgross@...e.com>, Thomas Gleixner <tglx@...utronix.de>,
 Borislav Petkov <bp@...en8.de>, Peter Zijlstra <peterz@...radead.org>,
 Josh Poimboeuf <jpoimboe@...nel.org>,
 Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
 Ingo Molnar <mingo@...hat.com>, Dave Hansen <dave.hansen@...ux.intel.com>,
 "x86@...nel.org" <x86@...nel.org>, "H . Peter Anvin" <hpa@...or.com>,
 Alexander Graf <graf@...zon.com>,
 Boris Ostrovsky <boris.ostrovsky@...cle.com>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [RFC PATCH 34/56] x86/alternative: Save old bytes for
 alternatives

On 10/30/25 16:39, Kaplan, David wrote:
<snip>

>>
> 
> Yes, there is an 8B pointer to each allocation (although I didn't include that in the number above).
> 
> There's a number of ways to optimize this, doing a single 'big buffer' with perhaps a 32-bit index seems rather straightforward.  And maybe there are then further ways to squeeze this.  But I think we're really talking about a small amount of memory, especially compared to the other overhead noted above.
> 

I spoke with Vlastimil who's a lot more familiar with MM and he said 
that allocations made early in the boot are likely to fall within the 
same 2mb block so actually what we are discussing here might very well 
fall within  "premature optimisation" land.

> Thanks
> --David Kaplan