linux-kernel - Re: [PATCH v2 3/3] mm/slub: Use percpu partial free counter

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Date:   Wed, 3 Mar 2021 20:15:58 +0100 (CET)
From:   Christoph Lameter <cl@...two.de>
To:     Matthew Wilcox <willy@...radead.org>
cc:     Xunlei Pang <xlpang@...ux.alibaba.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Wen Yang <wenyang@...ux.alibaba.com>,
        Roman Gushchin <guro@...com>, Pekka Enberg <penberg@...il.com>,
        Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
        David Rientjes <rientjes@...gle.com>,
        linux-kernel@...r.kernel.org,
        "linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH v2 3/3] mm/slub: Use percpu partial free counter

On Wed, 3 Mar 2021, Matthew Wilcox wrote:

> On Tue, Mar 02, 2021 at 10:14:53AM +0100, Christoph Lameter wrote:
> > On Mon, 10 Aug 2020, Xunlei Pang wrote:
> > > -	atomic_long_t partial_free_objs;
> > > +	atomic_long_t __percpu *partial_free_objs;
> >
> > A percpu counter is never atomic. Just use unsigned long and use this_cpu
> > operations for this thing. That should cut down further on the overhead.
>
> What about allocations from interrupt context?  Should this be a local_t
> instead?

Can this be allocated in an interrupt context?

And I am not sure how local_t relates to that? Percpu counters can be used
in an interrupt context without the overhead of the address calculations
that are required by a local_t.