From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757707Ab3A1SAG (ORCPT ); Mon, 28 Jan 2013 13:00:06 -0500 Received: from mail-qc0-f174.google.com ([209.85.216.174]:63007 "EHLO mail-qc0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757680Ab3A1R76 (ORCPT ); Mon, 28 Jan 2013 12:59:58 -0500 Date: Mon, 28 Jan 2013 09:59:51 -0800 From: Tejun Heo To: Kent Overstreet Cc: Rusty Russell , linux-kernel@vger.kernel.org, linux-aio@kvack.org, linux-fsdevel@vger.kernel.org, zab@redhat.com, bcrl@kvack.org, jmoyer@redhat.com, axboe@kernel.dk, viro@zeniv.linux.org.uk, tytso@mit.edu, Oleg Nesterov , srivatsa.bhat@linux.vnet.ibm.com, Christoph Lameter , "Paul E. McKenney" Subject: Re: [PATCH 23/32] Generic dynamic per cpu refcounting Message-ID: <20130128175951.GA22465@mtj.dyndns.org> References: <1356573611-18590-1-git-send-email-koverstreet@google.com> <1356573611-18590-26-git-send-email-koverstreet@google.com> <20130125005136.GE2373@mtj.dyndns.org> <87libhpz4h.fsf@rustcorp.com.au> <20130128175304.GX26407@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130128175304.GX26407@google.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, Kent. On Mon, Jan 28, 2013 at 09:53:04AM -0800, Kent Overstreet wrote: > > Like Tejun, I'd prefer to see it always alloc up-front, because it > > avoids the _noalloc variant (which is backwards: please hand gfp_t, so > > you don't hide the alloc) and heuristics. > > Problem with gfp_t is alloc_percpu() doesn't take it. I don't know why, > but this all goes away with Tejun's idea for allocating from a pool > refilled by workqueue. It goes down to how we allocate page tables. percpu depends on vmalloc space allocation which in turn depends on page table allocation which unfortunately assumes GFP_KERNEL and is spread all across different architectures. Adding @gfp to it came up a couple times but the cases weren't strong enough to push it all the way through. There are some aspects that I like about forcing GFP_KERNEL on all percpu allocations but if there are strong enough cases and someone is willing enough to push it through, maybe. Thanks. -- tejun