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

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Date:   Mon, 22 Jun 2020 11:03:23 -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 22, 2020 at 10:40 AM Roman Gushchin <guro@...com> wrote:
>
> On Mon, Jun 22, 2020 at 10:29:29AM -0700, Shakeel Butt wrote:
> > 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.
>
> Simple because some kmem_caches are created very early, so we don't
> even know at that time if we will need memcg slab caches. But this
> code is likely going away if we're going with a single set for all
> allocations.
>

LGTM.

Reviewed-by: Shakeel Butt <shakeelb@...gle.com>