linux-kernel - Re: [PATCH v3 09/14] x86: Minimal SLAB alignment

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Message-ID: <czzcsmwaf42v47arvmwgrh4p7h3misoarremtc7r2cme2ceuud@yya5jfuqhuye>
Date: Wed, 9 Apr 2025 14:49:02 +0200
From: Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>
To: Dave Hansen <dave.hansen@...el.com>
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Subject: Re: [PATCH v3 09/14] x86: Minimal SLAB alignment

On 2025-04-04 at 09:59:49 -0700, Dave Hansen wrote:
>On 4/4/25 06:14, Maciej Wieczor-Retman wrote:
>> Adjust x86 minimal SLAB alignment to match KASAN granularity size. In
>> tag-based mode the size changes to 16 bytes so the value needs to be 16.
>
>I feel like we need a _bit_ of a discussion of the impact here. We are,
>after all, trying to get this feature into shape so that it can be used
>more widely outside of just debugging environments.
>
>What's the impact of this in a production environment?

I tried booting a fedora 41 on a Sierra Forest system with KASAN disabled
(disabled only the reports so the 8 byte alignment doesn't cause a wall of debug
information). Did so for both 8 byte alignment (default) and 16 byte alignment
(added by the series).

The differences looked mostly like noise, sometimes the higher alignment would
use up a little bit less memory, sometimes a little bit more. I looked at all
values in "cat /proc/meminfo".

Is there some slab/slub benchmark for the kernel that would make sense to
checkout here?

-- 
Kind regards
Maciej Wieczór-Retman