linux-kernel - Re: [PATCH 5/5] [DEBUG] slab: Report number of NULLings

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Message-ID: <e3437446-798d-f4f3-11d7-675f8886575b@gentwo.org>
Date: Mon, 24 Mar 2025 09:16:47 -0700 (PDT)
From: "Christoph Lameter (Ampere)" <cl@...two.org>
To: Kees Cook <kees@...nel.org>
cc: Vlastimil Babka <vbabka@...e.cz>, Pekka Enberg <penberg@...nel.org>, 
    David Rientjes <rientjes@...gle.com>, Joonsoo Kim <iamjoonsoo.kim@....com>, 
    Andrew Morton <akpm@...ux-foundation.org>, 
    Roman Gushchin <roman.gushchin@...ux.dev>, 
    Hyeonggon Yoo <42.hyeyoo@...il.com>, linux-mm@...ck.org, 
    Miguel Ojeda <ojeda@...nel.org>, Nathan Chancellor <nathan@...nel.org>, 
    Marco Elver <elver@...gle.com>, Nick Desaulniers <ndesaulniers@...gle.com>, 
    Przemek Kitszel <przemyslaw.kitszel@...el.com>, 
    linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH 5/5] [DEBUG] slab: Report number of NULLings

On Fri, 21 Mar 2025, Kees Cook wrote:

> diff --git a/include/linux/slab.h b/include/linux/slab.h
> index 2717ad238fa2..a4740c8b6ccb 100644
> --- a/include/linux/slab.h
> +++ b/include/linux/slab.h
> @@ -469,6 +469,8 @@ void __kfree(const void *objp);
>  void __kfree_sensitive(const void *objp);
>  size_t __ksize(const void *objp);
>
> +extern atomic_t count_nulled;

That is a scalability issue. Use a vmstat counter instead?