Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932259AbdLTK0c (ORCPT ); Wed, 20 Dec 2017 05:26:32 -0500 Received: from mga03.intel.com ([134.134.136.65]:34223 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754328AbdLTK01 (ORCPT ); Wed, 20 Dec 2017 05:26:27 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.45,431,1508828400"; d="scan'208";a="14182955" Subject: Re: [PATCH v2 4/5] mm: use node_page_state_snapshot to avoid deviation To: Michal Hocko Cc: Greg Kroah-Hartman , Andrew Morton , Vlastimil Babka , Mel Gorman , Johannes Weiner , Christopher Lameter , YASUAKI ISHIMATSU , Andrey Ryabinin , Nikolay Borisov , Pavel Tatashin , David Rientjes , Sebastian Andrzej Siewior , Dave , Andi Kleen , Tim Chen , Jesper Dangaard Brouer , Ying Huang , Aaron Lu , Aubrey Li , Linux MM , Linux Kernel References: <1513665566-4465-1-git-send-email-kemi.wang@intel.com> <1513665566-4465-5-git-send-email-kemi.wang@intel.com> <20171219124317.GP2787@dhcp22.suse.cz> <94187fd5-ad70-eba7-2724-0fe5bed750d6@intel.com> <20171220100650.GI4831@dhcp22.suse.cz> From: kemi Message-ID: <1f3a6d05-2756-93fd-a380-df808c94ece8@intel.com> Date: Wed, 20 Dec 2017 18:24:24 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.5.0 MIME-Version: 1.0 In-Reply-To: <20171220100650.GI4831@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4441 Lines: 106 On 2017年12月20日 18:06, Michal Hocko wrote: > On Wed 20-12-17 14:07:35, kemi wrote: >> >> >> On 2017年12月19日 20:43, Michal Hocko wrote: >>> On Tue 19-12-17 14:39:25, Kemi Wang wrote: >>>> To avoid deviation, this patch uses node_page_state_snapshot instead of >>>> node_page_state for node page stats query. >>>> e.g. cat /proc/zoneinfo >>>> cat /sys/devices/system/node/node*/vmstat >>>> cat /sys/devices/system/node/node*/numastat >>>> >>>> As it is a slow path and would not be read frequently, I would worry about >>>> it. >>> >>> The changelog doesn't explain why these counters needs any special >>> treatment. _snapshot variants where used only for internal handling >>> where the precision really mattered. We do not have any in-tree user and >>> Jack has removed this by http://lkml.kernel.org/r/20171122094416.26019-1-jack@suse.cz >>> which is already sitting in the mmotm tree. We can re-add it but that >>> would really require a _very good_ reason. >>> >> >> Assume we have *nr* cpus, and threshold size is *t*. Thus, the maximum deviation is nr*t. >> Currently, Skylake platform has hundreds of CPUs numbers and the number is still >> increasing. Also, even the threshold size is kept to 125 at maximum (32765 >> for NUMA counters now), the deviation is just a little too big as I have mentioned in >> the log. I tend to sum the number in local cpus up when query the global stats. > > This is a general problem of pcp accounting. So if it needs to be > addressed then do it the same way for all stats. > >> Also, node_page_state_snapshot is only called in slow path and I don't think that >> would be a big problem. >> >> Anyway, it is a matter of taste. I just think it's better to have. > > You are making numastats special and I yet haven't heard any sounds > arguments for that. But that should be discussed in the respective > patch. > That is because we have much larger threshold size for NUMA counters, that means larger deviation. So, the number in local cpus may not be simply ignored. >>>> Signed-off-by: Kemi Wang >>>> --- >>>> drivers/base/node.c | 17 ++++++++++------- >>>> mm/vmstat.c | 2 +- >>>> 2 files changed, 11 insertions(+), 8 deletions(-) >>>> >>>> diff --git a/drivers/base/node.c b/drivers/base/node.c >>>> index a045ea1..cf303f8 100644 >>>> --- a/drivers/base/node.c >>>> +++ b/drivers/base/node.c >>>> @@ -169,12 +169,15 @@ static ssize_t node_read_numastat(struct device *dev, >>>> "interleave_hit %lu\n" >>>> "local_node %lu\n" >>>> "other_node %lu\n", >>>> - node_page_state(NODE_DATA(dev->id), NUMA_HIT), >>>> - node_page_state(NODE_DATA(dev->id), NUMA_MISS), >>>> - node_page_state(NODE_DATA(dev->id), NUMA_FOREIGN), >>>> - node_page_state(NODE_DATA(dev->id), NUMA_INTERLEAVE_HIT), >>>> - node_page_state(NODE_DATA(dev->id), NUMA_LOCAL), >>>> - node_page_state(NODE_DATA(dev->id), NUMA_OTHER)); >>>> + node_page_state_snapshot(NODE_DATA(dev->id), NUMA_HIT), >>>> + node_page_state_snapshot(NODE_DATA(dev->id), NUMA_MISS), >>>> + node_page_state_snapshot(NODE_DATA(dev->id), >>>> + NUMA_FOREIGN), >>>> + node_page_state_snapshot(NODE_DATA(dev->id), >>>> + NUMA_INTERLEAVE_HIT), >>>> + node_page_state_snapshot(NODE_DATA(dev->id), NUMA_LOCAL), >>>> + node_page_state_snapshot(NODE_DATA(dev->id), >>>> + NUMA_OTHER)); >>>> } >>>> >>>> static DEVICE_ATTR(numastat, S_IRUGO, node_read_numastat, NULL); >>>> @@ -194,7 +197,7 @@ static ssize_t node_read_vmstat(struct device *dev, >>>> for (i = 0; i < NR_VM_NODE_STAT_ITEMS; i++) >>>> n += sprintf(buf+n, "%s %lu\n", >>>> vmstat_text[i + NR_VM_ZONE_STAT_ITEMS], >>>> - node_page_state(pgdat, i)); >>>> + node_page_state_snapshot(pgdat, i)); >>>> >>>> return n; >>>> } >>>> diff --git a/mm/vmstat.c b/mm/vmstat.c >>>> index 64e08ae..d65f28d 100644 >>>> --- a/mm/vmstat.c >>>> +++ b/mm/vmstat.c >>>> @@ -1466,7 +1466,7 @@ static void zoneinfo_show_print(struct seq_file *m, pg_data_t *pgdat, >>>> for (i = 0; i < NR_VM_NODE_STAT_ITEMS; i++) { >>>> seq_printf(m, "\n %-12s %lu", >>>> vmstat_text[i + NR_VM_ZONE_STAT_ITEMS], >>>> - node_page_state(pgdat, i)); >>>> + node_page_state_snapshot(pgdat, i)); >>>> } >>>> } >>>> seq_printf(m, >>>> -- >>>> 2.7.4 >>>> >>> >