linux-kernel - Re: [RFC 02/26] mm, slub: allocate private object map for validate_slab

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Date:   Tue, 25 May 2021 11:17:42 +0100
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Christoph Lameter <cl@...ux.com>,
        David Rientjes <rientjes@...gle.com>,
        Pekka Enberg <penberg@...nel.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Jann Horn <jannh@...gle.com>
Subject: Re: [RFC 02/26] mm, slub: allocate private object map for
 validate_slab_cache()

On Tue, May 25, 2021 at 01:39:22AM +0200, Vlastimil Babka wrote:
> validate_slab_cache() is called either to handle a sysfs write, or from a
> self-test context. In both situations it's straightforward to preallocate a
> private object bitmap instead of grabbing the shared static one meant for
> critical sections, so let's do that.
> 
> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
>
> <SNIP>
>
> @@ -4685,10 +4685,17 @@ static long validate_slab_cache(struct kmem_cache *s)
>  	int node;
>  	unsigned long count = 0;
>  	struct kmem_cache_node *n;
> +	unsigned long *obj_map;
> +
> +	obj_map = bitmap_alloc(oo_objects(s->oo), GFP_KERNEL);
> +	if (!obj_map)
> +		return -ENOMEM;
>  


Most callers of validate_slab_cache don't care about the return value
except when the validate sysfs file is written. Should a simply
informational message be displayed for -ENOMEM in case a writer to
validate fails and it's not obvious it was because of an allocation
failure?

It's a fairly minor concern so whether you add a message or not

Acked-by: Mel Gorman <mgorman@...hsingularity.net>

-- 
Mel Gorman
SUSE Labs