linux-kernel - Re: [PATCH v6 13/19] mm: memcg/slab: simplify memcg cache creation

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Message-ID: <CALvZod50rUqhknV50zwvm4sLxdP=OWCLqFRKPPO_8Pff_v4EOg@mail.gmail.com>
Date:   Mon, 22 Jun 2020 10:29:29 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Roman Gushchin <guro@...com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Lameter <cl@...ux.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Linux MM <linux-mm@...ck.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Kernel Team <kernel-team@...com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 13/19] mm: memcg/slab: simplify memcg cache creation

On Mon, Jun 8, 2020 at 4:07 PM Roman Gushchin <guro@...com> wrote:
>
> Because the number of non-root kmem_caches doesn't depend on the
> number of memory cgroups anymore and is generally not very big,
> there is no more need for a dedicated workqueue.
>
> Also, as there is no more need to pass any arguments to the
> memcg_create_kmem_cache() except the root kmem_cache, it's
> possible to just embed the work structure into the kmem_cache
> and avoid the dynamic allocation of the work structure.
>
> This will also simplify the synchronization: for each root kmem_cache
> there is only one work. So there will be no more concurrent attempts
> to create a non-root kmem_cache for a root kmem_cache: the second and
> all following attempts to queue the work will fail.
>
>
> On the kmem_cache destruction path there is no more need to call the
> expensive flush_workqueue() and wait for all pending works to be
> finished. Instead, cancel_work_sync() can be used to cancel/wait for
> only one work.
>
> Signed-off-by: Roman Gushchin <guro@...com>
> Reviewed-by: Vlastimil Babka <vbabka@...e.cz>

Why not pre-allocate the non-root kmem_cache at the kmem_cache
creation time? No need for work_struct, queue_work() or
cancel_work_sync() at all.