linux-kernel - Re: [PATCH v4 2/2] mm: avoid slub allocation while holding list

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Message-ID: <alpine.DEB.2.21.1911092313460.32415@www.lameter.com>
Date:   Sat, 9 Nov 2019 23:16:28 +0000 (UTC)
From:   Christopher Lameter <cl@...ux.com>
To:     Yu Zhao <yuzhao@...gle.com>
cc:     Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH v4 2/2] mm: avoid slub allocation while holding
 list_lock

On Sat, 9 Nov 2019, Yu Zhao wrote:

> >  	struct page *page, *h;
> > +	unsigned long *map = bitmap_alloc(oo_objects(s->max), GFP_KERNEL);
> > +
> > +	if (!map)
> > +		return;
>
> What would happen if we are trying to allocate from the slab that is
> being shut down? And shouldn't the allocation be conditional (i.e.,
> only when CONFIG_SLUB_DEBUG=y)?

Kmalloc slabs are never shut down.

The allocation does not hurt and CONFIG_SLUB_DEBUG is on in most
configurations.