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

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Message-ID: <20190226163151.GA47262@dennisz-mbp.dhcp.thefacebook.com>
Date:   Tue, 26 Feb 2019 11:31:51 -0500
From:   Dennis Zhou <dennis@...nel.org>
To:     Christopher Lameter <cl@...ux.com>
Cc:     "dennis@...nel.org" <dennis@...nel.org>,
        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 Tue, Feb 26, 2019 at 03:15:50PM +0000, Christopher Lameter wrote:
> 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.
> 

Okay. I'll apply it with your ack if that's fine.

Thanks,
Dennis