linux-kernel - Re: [PATCH 2/2] percpu: km: no need to consider pcpu_group

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Date:   Tue, 26 Feb 2019 15:15:50 +0000
From:   Christopher Lameter <cl@...ux.com>
To:     "dennis@...nel.org" <dennis@...nel.org>
cc:     Peng Fan <peng.fan@....com>, "tj@...nel.org" <tj@...nel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "van.freenix@...il.com" <van.freenix@...il.com>
Subject: Re: [PATCH 2/2] percpu: km: no need to consider
 pcpu_group_offsets[0]

On Mon, 25 Feb 2019, dennis@...nel.org wrote:

> > @@ -67,7 +67,7 @@ static struct pcpu_chunk *pcpu_create_chunk(gfp_t gfp)
> >  		pcpu_set_page_chunk(nth_page(pages, i), chunk);
> >
> >  	chunk->data = pages;
> > -	chunk->base_addr = page_address(pages) - pcpu_group_offsets[0];
> > +	chunk->base_addr = page_address(pages);
> >
> >  	spin_lock_irqsave(&pcpu_lock, flags);
> >  	pcpu_chunk_populated(chunk, 0, nr_pages, false);
> > --
> > 2.16.4
> >
>
> While I do think you're right, creating a chunk is not a part of the
> critical path and subtracting 0 is incredibly minor overhead. So I'd
> rather keep the code as is to maintain consistency between percpu-vm.c
> and percpu-km.c.

Well it is confusing if there the expression is there but never used. It
is clearer with the patch.