From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754051AbYKPFsW (ORCPT ); Sun, 16 Nov 2008 00:48:22 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751202AbYKPFsH (ORCPT ); Sun, 16 Nov 2008 00:48:07 -0500 Received: from smtp1.linux-foundation.org ([140.211.169.13]:54717 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751108AbYKPFsG (ORCPT ); Sun, 16 Nov 2008 00:48:06 -0500 Date: Sat, 15 Nov 2008 21:47:35 -0800 From: Andrew Morton To: Lai Jiangshan Cc: Arjan van de Ven , Paul Menage , kamezawa.hiroyu@jp.fujitsu.com, Balbir Singh , Jens Axboe , "David S. Miller" , Jan Kara , Jes Sorensen , Linux Kernel Mailing List Subject: Re: [PATCH 1/7] mm: introduce simple_malloc()/simple_free() Message-Id: <20081115214735.8f6ab585.akpm@linux-foundation.org> In-Reply-To: <491FB107.6050703@cn.fujitsu.com> References: <491FA28B.2070003@cn.fujitsu.com> <20081115205229.765f7ee3@infradead.org> <20081115210334.3870cdf6.akpm@linux-foundation.org> <491FB107.6050703@cn.fujitsu.com> X-Mailer: Sylpheed 2.4.8 (GTK+ 2.12.5; x86_64-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 16 Nov 2008 13:35:03 +0800 Lai Jiangshan wrote: > Andrew Morton wrote: > > On Sat, 15 Nov 2008 20:52:29 -0800 Arjan van de Ven wrote: > > > >> On Sun, 16 Nov 2008 12:33:15 +0800 > >> Lai Jiangshan wrote: > >> > >>> some subsystem needs vmalloc() when required memory is large. > >>> but current kernel has not APIs for this requirement. > >>> this patch introduces simple_malloc() and simple_free(). > >> Hi > >> > >> I kinda really don't like this approach. vmalloc() (and especially, > >> vfree()) is a really expensive operation, and vmalloc()'d memory is > >> also slower (due to tlb pressure). > > > > And it can fragment, which effectively means a dead box. > > > >> Realistically, people should try hard > >> to use small datastructure instead.... > > > > Yup, it makes it easier for people to do something which we strongly > > discourage. The risk got worse with all these 64-bit machines with > > vast amounts of virtual address space. It makes it easier for people > > to develop and "test" code which isn't reliable on smaller machines. > > > > > > vmalloc() is not good for performance and increasing fragment. > but vmalloc() is need for some subsystems' alternative malloc, > like cgroup's tasks file and other subsystems(about 20 subsystems). > > these subsystems use kmalloc() in the most condition, but may need > vmalloc() in some rare condition. so they use alternative malloc. > > So, since these subsystems' maintainer have good reasons for using vmalloc(), > they can use simple_malloc() too. simple_malloc() is not for common using. > (I should document when we use simple_malloc() in the code) > > simple_free() is useful. there are several subsystems which use a flags > for selecting kfree() or vfree(), and some subsystems recount the size hardy > before kfree() or vfree(). > Sure. Apart from the names of the functions, it's a good cleanup of existing code. It's just that we must *really* discourage the use of vmalloc :( Maybe we should call it i_am_a_hopeless_loser_alloc(). Sending the per-subsystem patches to the maintainers would be fun.