linux-kernel - Re: [PATCH] slub: fix __kmem_cache_empty for !CONFIG_SLUB

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Date:   Wed, 20 Jun 2018 14:36:33 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Andrey Ryabinin <aryabinin@...tuozzo.com>
Cc:     "Jason A . Donenfeld" <Jason@...c4.com>,
        Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        stable@...r.kernel.org
Subject: Re: [PATCH] slub: fix __kmem_cache_empty for !CONFIG_SLUB_DEBUG

On Wed, Jun 20, 2018 at 5:08 AM Andrey Ryabinin <aryabinin@...tuozzo.com> wrote:
>
>
>
> On 06/20/2018 12:33 AM, Shakeel Butt wrote:
> > For !CONFIG_SLUB_DEBUG, SLUB does not maintain the number of slabs
> > allocated per node for a kmem_cache. Thus, slabs_node() in
> > __kmem_cache_empty() will always return 0. So, in such situation, it is
> > required to check per-cpu slabs to make sure if a kmem_cache is empty or
> > not.
> >
> > Please note that __kmem_cache_shutdown() and __kmem_cache_shrink() are
> > not affected by !CONFIG_SLUB_DEBUG as they call flush_all() to clear
> > per-cpu slabs.
>
> So what? Yes, they call flush_all() and then check if there are non-empty slabs left.
> And that check doesn't work in case of disabled CONFIG_SLUB_DEBUG.
> How is flush_all() or per-cpu slabs even relevant here?
>

The flush_all() will move all cpu slabs and partials to node's partial
list and thus later check of node's partial list will handle non-empty
slabs situation. However what I missed is the 'full slabs' which are
not on any list for !CONFIG_SLUB_DEBUG. So, this patch is not the
complete solution. I think David's suggestion is the complete
solution. I will post a patch based on David's suggestion.