linux-kernel - Re: [PATCH v2] mm: kmemleak: Use mempool allocations for kmemleak objects

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Message-Id: <20190730125743.113e59a9c449847d7f6ae7c3@linux-foundation.org>
Date:   Tue, 30 Jul 2019 12:57:43 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Catalin Marinas <catalin.marinas@....com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Michal Hocko <mhocko@...nel.org>,
        Matthew Wilcox <willy@...radead.org>, Qian Cai <cai@....pw>
Subject: Re: [PATCH v2] mm: kmemleak: Use mempool allocations for kmemleak
 objects

On Sat, 27 Jul 2019 14:23:33 +0100 Catalin Marinas <catalin.marinas@....com> wrote:

> Add mempool allocations for struct kmemleak_object and
> kmemleak_scan_area as slightly more resilient than kmem_cache_alloc()
> under memory pressure. Additionally, mask out all the gfp flags passed
> to kmemleak other than GFP_KERNEL|GFP_ATOMIC.
> 
> A boot-time tuning parameter (kmemleak.mempool) is added to allow a
> different minimum pool size (defaulting to NR_CPUS * 4).

Why would anyone ever want to alter this?  Is there some particular
misbehaviour which this will improve?  If so, what is it?

> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -2011,6 +2011,12 @@
>  			Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
>  			the default is off.
>  
> +	kmemleak.mempool=
> +			[KNL] Boot-time tuning of the minimum kmemleak
> +			metadata pool size.
> +			Format: <int>
> +			Default: NR_CPUS * 4
> +

This is the only documentation we provide people and it doesn't really
explain anything at all.  IOW, can we do a better job of explaining all this
to the target audience?

Why does the min size need to be tunable anyway?