Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752234AbdFVQbs (ORCPT ); Thu, 22 Jun 2017 12:31:48 -0400 Received: from smtp.codeaurora.org ([198.145.29.96]:40002 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750969AbdFVQbq (ORCPT ); Thu, 22 Jun 2017 12:31:46 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org 542B660132 Authentication-Results: pdx-caf-mail.web.codeaurora.org; dmarc=none (p=none dis=none) header.from=codeaurora.org Authentication-Results: pdx-caf-mail.web.codeaurora.org; spf=none smtp.mailfrom=stummala@codeaurora.org Subject: Re: [PATCH v2] fs/dcache.c: fix spin lockup issue on nlru->lock To: Vladimir Davydov Cc: Alexander Polakov , Andrew Morton , Jan Kara , viro@zeniv.linux.org.uk, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org References: <6ab790fe-de97-9495-0d3b-804bae5d7fbb@codeaurora.org> <1498027155-4456-1-git-send-email-stummala@codeaurora.org> <20170621163134.GA3273@esperanza> From: Sahitya Tummala Message-ID: <8d82c32d-6cbb-c39d-2f0e-0af23925b3c1@codeaurora.org> Date: Thu, 22 Jun 2017 22:01:39 +0530 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.2.0 MIME-Version: 1.0 In-Reply-To: <20170621163134.GA3273@esperanza> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2213 Lines: 57 On 6/21/2017 10:01 PM, Vladimir Davydov wrote: > >> index cddf397..c8ca150 100644 >> --- a/fs/dcache.c >> +++ b/fs/dcache.c >> @@ -1133,10 +1133,11 @@ void shrink_dcache_sb(struct super_block *sb) >> LIST_HEAD(dispose); >> >> freed = list_lru_walk(&sb->s_dentry_lru, >> - dentry_lru_isolate_shrink, &dispose, UINT_MAX); >> + dentry_lru_isolate_shrink, &dispose, 1024); >> >> this_cpu_sub(nr_dentry_unused, freed); >> shrink_dentry_list(&dispose); >> + cond_resched(); >> } while (freed > 0); > In an extreme case, a single invocation of list_lru_walk() can skip all > 1024 dentries, in which case 'freed' will be 0 forcing us to break the > loop prematurely. I think we should loop until there's at least one > dentry left on the LRU, i.e. > > while (list_lru_count(&sb->s_dentry_lru) > 0) > > However, even that wouldn't be quite correct, because list_lru_count() > iterates over all memory cgroups to sum list_lru_one->nr_items, which > can race with memcg offlining code migrating dentries off a dead cgroup > (see memcg_drain_all_list_lrus()). So it looks like to make this check > race-free, we need to account the number of entries on the LRU not only > per memcg, but also per node, i.e. add list_lru_node->nr_items. > Fortunately, list_lru entries can't be migrated between NUMA nodes. It looks like list_lru_count() is iterating per node before iterating over all memory cgroups as below - unsigned long list_lru_count_node(struct list_lru *lru, int nid) { long count = 0; int memcg_idx; count += __list_lru_count_one(lru, nid, -1); if (list_lru_memcg_aware(lru)) { for_each_memcg_cache_index(memcg_idx) count += __list_lru_count_one(lru, nid, memcg_idx); } return count; } The first call to __list_lru_count_one() is iterating all the items per node i.e, nlru->lru->nr_items. Is my understanding correct? If not, could you please clarify on how to get the lru items per node? -- Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc. Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project.