linux-kernel - Re: [RFC 01/26] mm, slub: allocate private object map for sysfs listings

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Date:   Tue, 25 May 2021 10:06:31 +0200 (CEST)
From:   Christoph Lameter <cl@...two.de>
To:     Vlastimil Babka <vbabka@...e.cz>
cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        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>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Jann Horn <jannh@...gle.com>
Subject: Re: [RFC 01/26] mm, slub: allocate private object map for sysfs
 listings

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@...ux.com>