linux-kernel - Re: [PATCH RFC 14/20] mempool: introduce mempool_use_prealloc

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Message-ID: <ZV44eczk0L_ihkwi@elver.google.com>
Date:   Wed, 22 Nov 2023 18:20:57 +0100
From:   Marco Elver <elver@...gle.com>
To:     andrey.konovalov@...ux.dev
Cc:     Alexander Potapenko <glider@...gle.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        kasan-dev@...glegroups.com, Evgenii Stepanov <eugenis@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Andrey Konovalov <andreyknvl@...gle.com>
Subject: Re: [PATCH RFC 14/20] mempool: introduce mempool_use_prealloc_only

On Mon, Nov 06, 2023 at 09:10PM +0100, andrey.konovalov@...ux.dev wrote:
> From: Andrey Konovalov <andreyknvl@...gle.com>
> 
> Introduce a new mempool_use_prealloc_only API that tells the mempool to
> only use the elements preallocated during the mempool's creation and to
> not attempt allocating new ones.
> 
> This API is required to test the KASAN poisoning/unpoisoning functinality
> in KASAN tests, but it might be also useful on its own.
> 
> Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
> ---
>  include/linux/mempool.h |  2 ++
>  mm/mempool.c            | 27 ++++++++++++++++++++++++---
>  2 files changed, 26 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/mempool.h b/include/linux/mempool.h
> index 4aae6c06c5f2..822adf1e7567 100644
> --- a/include/linux/mempool.h
> +++ b/include/linux/mempool.h
> @@ -18,6 +18,7 @@ typedef struct mempool_s {
>  	int min_nr;		/* nr of elements at *elements */
>  	int curr_nr;		/* Current nr of elements at *elements */
>  	void **elements;
> +	bool use_prealloc_only;	/* Use only preallocated elements */

This increases the struct size from 56 to 64 bytes (64 bit arch).
mempool_t is embedded in lots of other larger structs, and this may
result in some unwanted bloat.

Is there a way to achieve the same thing without adding a new bool to
the mempool struct?

It seems a little excessive only for the purpose of the tests.