Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752851AbbKCOLZ (ORCPT ); Tue, 3 Nov 2015 09:11:25 -0500 Received: from mail-pa0-f41.google.com ([209.85.220.41]:35638 "EHLO mail-pa0-f41.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751229AbbKCOLX (ORCPT ); Tue, 3 Nov 2015 09:11:23 -0500 Subject: Re: [PATCH v6 2/3] percpu: add PERCPU_ATOM_SIZE for a generic percpu area setup Mime-Version: 1.0 (Apple Message framework v1283) Content-Type: text/plain; charset=us-ascii From: Jungseok Lee In-Reply-To: Date: Tue, 3 Nov 2015 23:11:16 +0900 Cc: catalin.marinas@arm.com, will.deacon@arm.com, tj@kernel.org, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, james.morse@arm.com, takahiro.akashi@linaro.org, mark.rutland@arm.com, barami97@gmail.com, linux-kernel@vger.kernel.org Content-Transfer-Encoding: 7bit Message-Id: <8FA31B91-D361-4F98-A2D3-EFC5D877EDB1@gmail.com> References: <1446363977-23656-1-git-send-email-jungseoklee85@gmail.com> <1446363977-23656-3-git-send-email-jungseoklee85@gmail.com> To: Christoph Lameter X-Mailer: Apple Mail (2.1283) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1257 Lines: 30 On Nov 3, 2015, at 1:10 AM, Christoph Lameter wrote: Dear Christoph, > On Sun, 1 Nov 2015, Jungseok Lee wrote: > >> There is no room to adjust 'atom_size' now when a generic percpu area >> is used. It would be redundant to write down an architecture-specific >> setup_per_cpu_areas() in order to only change the 'atom_size'. Thus, >> this patch adds a new definition, PERCPU_ATOM_SIZE, which is PAGE_SIZE >> by default. The value could be updated if needed by architecture. > > What is atom_size? Why would you want a difference allocation size here? > The percpu area is virtually mapped regardless. So you will have > contiguous addresses even without atom_size. I think Catalin have already written down a perfect explanation. I'd like memory with an alignment greater than PAGE_SIZE. But, __per_cpu_offset[] is PAGE_SIZE aligned under a generic setup_per_cpu_areas(). That is, secondary cores cannot get that kind of space. Thanks for taking a look at this doubtable change! Best Regards Jungseok Lee -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/