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Date:   Tue, 25 May 2021 10:06:31 +0200 (CEST)
From:   Christoph Lameter <cl@gentwo.de>
To:     Vlastimil Babka <vbabka@suse.cz>
cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        David Rientjes <rientjes@google.com>,
        Pekka Enberg <penberg@kernel.org>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Thomas Gleixner <tglx@linutronix.de>,
        Mel Gorman <mgorman@techsingularity.net>,
        Jesper Dangaard Brouer <brouer@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Jann Horn <jannh@google.com>
Subject: Re: [RFC 01/26] mm, slub: allocate private object map for sysfs
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In-Reply-To: <20210524233946.20352-2-vbabka@suse.cz>
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References: <20210524233946.20352-1-vbabka@suse.cz> <20210524233946.20352-2-vbabka@suse.cz>
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On Tue, 25 May 2021, Vlastimil Babka wrote:

> Slub has a static spinlock protected bitmap for marking which objects are on
> freelist when it wants to list them, for situations where dynamically
> allocating such map can lead to recursion or locking issues, and on-stack
> bitmap would be too large.
>
> The handlers of sysfs files alloc_calls and free_calls also currently use this
> shared bitmap, but their syscall context makes it straightforward to allocate a
> private map before entering locked sections, so switch these processing paths
> to use a private bitmap.

Right in that case a GFP_KERNEL allocation is fine and you can avoid the
static map.

Acked-by: Christoph Lameter <cl@linux.com>