From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ig0-f170.google.com (mail-ig0-f170.google.com [209.85.213.170]) by kanga.kvack.org (Postfix) with ESMTP id D6F726B0253 for ; Mon, 2 Nov 2015 13:11:34 -0500 (EST) Received: by igbdj2 with SMTP id dj2so59387260igb.1 for ; Mon, 02 Nov 2015 10:11:34 -0800 (PST) Received: from resqmta-ch2-10v.sys.comcast.net (resqmta-ch2-10v.sys.comcast.net. [2001:558:fe21:29:69:252:207:42]) by mx.google.com with ESMTPS id 143si12871236ioe.192.2015.11.02.10.11.34 for (version=TLSv1.2 cipher=RC4-SHA bits=128/128); Mon, 02 Nov 2015 10:11:34 -0800 (PST) Date: Mon, 2 Nov 2015 12:11:33 -0600 (CST) From: Christoph Lameter Subject: Re: [PATCH v6 2/3] percpu: add PERCPU_ATOM_SIZE for a generic percpu area setup In-Reply-To: <20151102173520.GC7637@e104818-lin.cambridge.arm.com> Message-ID: References: <1446363977-23656-1-git-send-email-jungseoklee85@gmail.com> <1446363977-23656-3-git-send-email-jungseoklee85@gmail.com> <20151102162236.GB7637@e104818-lin.cambridge.arm.com> <20151102173520.GC7637@e104818-lin.cambridge.arm.com> Content-Type: text/plain; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Catalin Marinas Cc: mark.rutland@arm.com, Jungseok Lee , linux-mm@kvack.org, barami97@gmail.com, will.deacon@arm.com, linux-kernel@vger.kernel.org, takahiro.akashi@linaro.org, james.morse@arm.com, tj@kernel.org, linux-arm-kernel@lists.infradead.org On Mon, 2 Nov 2015, Catalin Marinas wrote: > On Mon, Nov 02, 2015 at 10:48:17AM -0600, Christoph Lameter wrote: > > On Mon, 2 Nov 2015, Catalin Marinas wrote: > > > I haven't looked at the patch 3/3 in detail but I'm pretty sure I'll NAK > > > the approach (and the definition of PERCPU_ATOM_SIZE), therefore > > > rendering this patch unnecessary. IIUC, this is used to enforce some > > > alignment of the per-CPU IRQ stack to be able to check whether the > > > current stack is process or IRQ on exception entry. But there are other, > > > less intrusive ways to achieve the same (e.g. x86). > > > > The percpu allocator allows the specification of alignment requirements. > > Patch 3/3 does something like this: > > DEFINE_PER_CPU(char [IRQ_STACK_SIZE], irq_stacks) __aligned(IRQ_STACK_SIZE) > > where IRQ_STACK_SIZE > PAGE_SIZE. AFAICT, setup_per_cpu_areas() doesn't > guarantee alignment greater than PAGE_SIZE. And we cannot use percpu_alloc() instead? Aligning the whole of the percpu area because one allocation requires it? -- 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