From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f48.google.com (mail-pa0-f48.google.com [209.85.220.48]) by kanga.kvack.org (Postfix) with ESMTP id 64F8C6B0038 for ; Tue, 3 Nov 2015 09:11:24 -0500 (EST) Received: by padhx2 with SMTP id hx2so11870159pad.1 for ; Tue, 03 Nov 2015 06:11:24 -0800 (PST) Received: from mail-pa0-x22f.google.com (mail-pa0-x22f.google.com. [2607:f8b0:400e:c03::22f]) by mx.google.com with ESMTPS id yj5si39192455pbc.32.2015.11.03.06.11.23 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 03 Nov 2015 06:11:23 -0800 (PST) Received: by pabfh17 with SMTP id fh17so19689370pab.0 for ; Tue, 03 Nov 2015 06:11:23 -0800 (PST) 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 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> Sender: owner-linux-mm@kvack.org List-ID: To: Christoph Lameter 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 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, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org