From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933576AbcBQAxm (ORCPT ); Tue, 16 Feb 2016 19:53:42 -0500 Received: from mail-io0-f177.google.com ([209.85.223.177]:33486 "EHLO mail-io0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933513AbcBQAxk (ORCPT ); Tue, 16 Feb 2016 19:53:40 -0500 Subject: Re: Idea for reducing sysfs memory usage To: Greg Kroah-Hartman , Edward Cree References: <56C3B4E9.7030207@cantab.net> <20160216235502.GA14565@kroah.com> <56C3C0D2.9090407@cantab.net> <20160217004730.GA7558@kroah.com> Cc: linux-kernel@vger.kernel.org From: David Ahern Message-ID: <56C3C492.9040401@cumulusnetworks.com> Date: Tue, 16 Feb 2016 17:53:38 -0700 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.11; rv:38.0) Gecko/20100101 Thunderbird/38.6.0 MIME-Version: 1.0 In-Reply-To: <20160217004730.GA7558@kroah.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2/16/16 5:47 PM, Greg Kroah-Hartman wrote: > How many sysfs entries are you creating for that 20kb? And how did you > measure it? If you don't access the files, the backing store is not > allocated, saving you a lot of memory. If you do access it, it will be > freed later on afterward, so it's sometimes really hard to measure this > accurately. Using the kmem tracepoints: perf record -g \ -e kmem:kmalloc,kmem:kmem_cache_alloc,kmem:mm_page_alloc,kmem:kfree,kmem:kmem_cache_free,kmem:mm_page_free -- ip link add dummy1 type dummy First go round I painstakenly examined each allocation and location. After that I modified perf-kmem to do the summary for me for other use cases. I can forward the full notes if you want them. Here's the first few and last few: ################ # sysfs -- start # directory # device_add -> kobject_add -- register with generic layer ip 1732 [005] 27128.556548: kmem:kmalloc: ptr=0xffff8800ba9a5d60 bytes_req=7 bytes_alloc=32 gfp_flags=37748928 ffffffff8113e5ce __kmalloc_track_caller ([kernel.kallsyms]) ffffffff81116643 kstrdup ([kernel.kallsyms]) ffffffff8111667c kstrdup_const ([kernel.kallsyms]) ffffffff811a6bf5 __kernfs_new_node ([kernel.kallsyms]) ffffffff811a7397 kernfs_new_node ([kernel.kallsyms]) ffffffff811a7813 kernfs_create_dir_ns ([kernel.kallsyms]) ffffffff811a95f0 sysfs_create_dir_ns ([kernel.kallsyms]) ffffffff8126f76f kobject_add_internal ([kernel.kallsyms]) ffffffff8126fa62 kobject_add ([kernel.kallsyms]) ffffffff81319317 device_add ([kernel.kallsyms]) ffffffff81408528 netdev_register_kobject ([kernel.kallsyms]) ffffffff813f2cbb register_netdevice ([kernel.kallsyms]) ffffffff81401314 rtnl_newlink ([kernel.kallsyms]) # directory ip 1732 [005] 27128.556555: kmem:kmem_cache_alloc: ptr=0xffff8801399d6018 bytes_req=168 bytes_alloc=168 gfp_flags=37781696 ffffffff8113ee09 kmem_cache_alloc ([kernel.kallsyms]) ffffffff811a6c0e __kernfs_new_node ([kernel.kallsyms]) ffffffff811a7397 kernfs_new_node ([kernel.kallsyms]) ffffffff811a7813 kernfs_create_dir_ns ([kernel.kallsyms]) ffffffff811a95f0 sysfs_create_dir_ns ([kernel.kallsyms]) ffffffff8126f76f kobject_add_internal ([kernel.kallsyms]) ffffffff8126fa62 kobject_add ([kernel.kallsyms]) ffffffff81319317 device_add ([kernel.kallsyms]) ffffffff81408528 netdev_register_kobject ([kernel.kallsyms]) ffffffff813f2cbb register_netdevice ([kernel.kallsyms]) ffffffff81401314 rtnl_newlink ([kernel.kallsyms]) # device_add -> device_create_file(dev, &dev_attr_uevent) --> sysfs_create_file(&dev->kobj, &attr->attr) ip 1732 [005] 27128.556583: kmem:kmem_cache_alloc: ptr=0xffff8801399d60c0 bytes_req=168 bytes_alloc=168 gfp_flags=37781696 ffffffff8113ee09 kmem_cache_alloc ([kernel.kallsyms]) ffffffff811a6c0e __kernfs_new_node ([kernel.kallsyms]) ffffffff811a7397 kernfs_new_node ([kernel.kallsyms]) ffffffff811a8ac7 __kernfs_create_file ([kernel.kallsyms]) ffffffff811a9310 sysfs_add_file_mode_ns ([kernel.kallsyms]) ffffffff811a9370 sysfs_create_file_ns ([kernel.kallsyms]) ffffffff81317f3b device_create_file ([kernel.kallsyms]) ffffffff81319342 device_add ([kernel.kallsyms]) ffffffff81408528 netdev_register_kobject ([kernel.kallsyms]) ffffffff813f2cbb register_netdevice ([kernel.kallsyms]) ffffffff81401314 rtnl_newlink ([kernel.kallsyms]) ... ip 1732 [005] 27128.560734: kmem:kmem_cache_alloc: ptr=0xffff8800b94758a0 bytes_req=168 bytes_alloc=168 gfp_flags=37781696 ffffffff8113ee09 kmem_cache_alloc ([kernel.kallsyms]) ffffffff811a6c0e __kernfs_new_node ([kernel.kallsyms]) ffffffff811a7397 kernfs_new_node ([kernel.kallsyms]) ffffffff811a8ac7 __kernfs_create_file ([kernel.kallsyms]) ffffffff811a9310 sysfs_add_file_mode_ns ([kernel.kallsyms]) ffffffff811a9cd2 internal_create_group ([kernel.kallsyms]) ffffffff811a9e20 sysfs_create_group ([kernel.kallsyms]) ffffffff814083ca netdev_queue_update_kobjects ([kernel.kallsyms]) ffffffff81408583 netdev_register_kobject ([kernel.kallsyms]) ffffffff813f2cbb register_netdevice ([kernel.kallsyms]) ffffffff81401314 rtnl_newlink ([kernel.kallsyms]) ip 1732 [005] 27128.560789: kmem:kmem_cache_alloc: ptr=0xffff880139cd0400 bytes_req=256 bytes_alloc=256 gfp_flags=37748928 ffffffff8113ee09 kmem_cache_alloc ([kernel.kallsyms]) ffffffff813df48a __alloc_skb ([kernel.kallsyms]) ffffffff81270485 kobject_uevent_env ([kernel.kallsyms]) ffffffff81270703 kobject_uevent ([kernel.kallsyms]) ffffffff814083da netdev_queue_update_kobjects ([kernel.kallsyms]) ffffffff81408583 netdev_register_kobject ([kernel.kallsyms]) ffffffff813f2cbb register_netdevice ([kernel.kallsyms]) ffffffff81401314 rtnl_newlink ([kernel.kallsyms]) ip 1732 [005] 27128.560798: kmem:kmalloc: ptr=0xffff8800bab97c00 bytes_req=512 bytes_alloc=512 gfp_flags=37814976 ffffffff8113e5ce __kmalloc_track_caller ([kernel.kallsyms]) ffffffff813def36 __kmalloc_reserve.isra.50 ([kernel.kallsyms]) ffffffff813df4bc __alloc_skb ([kernel.kallsyms]) ffffffff81270485 kobject_uevent_env ([kernel.kallsyms]) ffffffff81270703 kobject_uevent ([kernel.kallsyms]) ffffffff814083da netdev_queue_update_kobjects ([kernel.kallsyms]) ffffffff81408583 netdev_register_kobject ([kernel.kallsyms]) ffffffff813f2cbb register_netdevice ([kernel.kallsyms]) ffffffff81401314 rtnl_newlink ([kernel.kallsyms]) # end netdev_register_kobject ###############################