From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751558AbeDDHSR (ORCPT ); Wed, 4 Apr 2018 03:18:17 -0400 Received: from aserp2120.oracle.com ([141.146.126.78]:52738 "EHLO aserp2120.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751470AbeDDHSP (ORCPT ); Wed, 4 Apr 2018 03:18:15 -0400 Subject: Re: [PATCH 2/2] kfree_rcu() should use kfree_bulk() interface To: Matthew Wilcox Cc: linux-kernel@vger.kernel.org, paulmck@linux.vnet.ibm.com, joe@perches.com, brouer@redhat.com, linux-mm@kvack.org References: <1522776173-7190-1-git-send-email-rao.shoaib@oracle.com> <1522776173-7190-3-git-send-email-rao.shoaib@oracle.com> <20180403205822.GB30145@bombadil.infradead.org> <20180404022347.GA17512@bombadil.infradead.org> From: Rao Shoaib Message-ID: <954a9ea2-5202-4ee3-1fa2-21acf8d07cdb@oracle.com> Date: Wed, 4 Apr 2018 00:16:06 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <20180404022347.GA17512@bombadil.infradead.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=8852 signatures=668697 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=2 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1711220000 definitions=main-1804040075 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/03/2018 07:23 PM, Matthew Wilcox wrote: > On Tue, Apr 03, 2018 at 05:55:55PM -0700, Rao Shoaib wrote: >> On 04/03/2018 01:58 PM, Matthew Wilcox wrote: >>> I think you might be better off with an IDR. The IDR can always >>> contain one entry, so there's no need for this 'rbf_list_head' or >>> __rcu_bulk_schedule_list. The IDR contains its first 64 entries in >>> an array (if that array can be allocated), so it's compatible with the >>> kfree_bulk() interface. >>> >> I have just familiarized myself with what IDR is by reading your article. If >> I am incorrect please correct me. >> >> The list and head you have pointed are only used  if the container can not >> be allocated. That could happen with IDR as well. Note that the containers >> are allocated at boot time and are re-used. > No, it can't happen with the IDR. The IDR can always contain one entry > without allocating anything. If you fail to allocate the second entry, > just free the first entry. > >> IDR seems to have some overhead, such as I have to specifically add the >> pointer and free the ID, plus radix tree maintenance. > ... what? Adding a pointer is simply idr_alloc(), and you get back an > integer telling you which index it has. Your data structure has its > own set of overhead. The only overhead is a pointer that points to the head and an int to keep count. If I use idr, I would have to allocate an struct idr which is much larger. idr_alloc()/idr_destroy() operations are much more costly than updating two pointers. As the pointers are stored in slots/nodes corresponding to the id, I would  have to retrieve the pointers by calling idr_remove() to pass them to be freed, the slots/nodes would constantly be allocated and freed. IDR is a very useful interface for allocating/managing ID's but I really do not see the justification for using it over here, perhaps you can elaborate more on the benefits and also on how I can just pass the array to be freed. Shoaib