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[209.85.220.65]) by mx.google.com with SMTPS id e123sor2369791ybb.190.2019.02.25.07.16.19 for (Google Transport Security); Mon, 25 Feb 2019 07:16:19 -0800 (PST) Received-SPF: pass (google.com: domain of dennisszhou@gmail.com designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; Authentication-Results: mx.google.com; spf=pass (google.com: domain of dennisszhou@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=dennisszhou@gmail.com; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=kernel.org X-Google-Smtp-Source: AHgI3IbPQDBBJv5dmRbrs6BvonMys2urOn/4rMhLOBnGs/VbY7xZxJp+i6QbgO4LmkeqW5c9WftOFg== X-Received: by 2002:a25:23ce:: with SMTP id j197mr6003459ybj.145.1551107779237; Mon, 25 Feb 2019 07:16:19 -0800 (PST) Received: from dennisz-mbp.dhcp.thefacebook.com ([2620:10d:c091:200::1:8bb9]) by smtp.gmail.com with ESMTPSA id d138sm1986291ywa.43.2019.02.25.07.16.17 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 25 Feb 2019 07:16:18 -0800 (PST) Date: Mon, 25 Feb 2019 10:16:16 -0500 From: "dennis@kernel.org" To: Peng Fan Cc: "tj@kernel.org" , "cl@linux.com" , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , "van.freenix@gmail.com" Subject: Re: [PATCH 2/2] percpu: km: no need to consider pcpu_group_offsets[0] Message-ID: <20190225151616.GB49611@dennisz-mbp.dhcp.thefacebook.com> References: <20190224132518.20586-1-peng.fan@nxp.com> <20190224132518.20586-2-peng.fan@nxp.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190224132518.20586-2-peng.fan@nxp.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Sun, Feb 24, 2019 at 01:13:50PM +0000, Peng Fan wrote: > percpu-km is used on UP systems which only has one group, > so the group offset will be always 0, there is no need > to subtract pcpu_group_offsets[0] when assigning chunk->base_addr > > Signed-off-by: Peng Fan > --- > mm/percpu-km.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/percpu-km.c b/mm/percpu-km.c > index 66e5598be876..8872c21a487b 100644 > --- a/mm/percpu-km.c > +++ b/mm/percpu-km.c > @@ -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. Thanks, Dennis