From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 74D22C433E0 for ; Fri, 19 Feb 2021 10:22:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2780164EC4 for ; Fri, 19 Feb 2021 10:22:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229678AbhBSKWN (ORCPT ); Fri, 19 Feb 2021 05:22:13 -0500 Received: from mx2.suse.de ([195.135.220.15]:58514 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229527AbhBSKWH (ORCPT ); Fri, 19 Feb 2021 05:22:07 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 5A3A4ACCF; Fri, 19 Feb 2021 10:21:25 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id 9D0271E14BC; Fri, 19 Feb 2021 11:21:25 +0100 (CET) Date: Fri, 19 Feb 2021 11:21:25 +0100 From: Jan Kara To: Amir Goldstein Cc: Jan Kara , linux-fsdevel Subject: Re: [PATCH 0/7] Performance improvement for fanotify merge Message-ID: <20210219102125.GB6086@quack2.suse.cz> References: <20210202162010.305971-1-amir73il@gmail.com> <20210216160258.GE21108@quack2.suse.cz> <20210217112539.GC14758@quack2.suse.cz> <20210218111558.GB16953@quack2.suse.cz> <20210219101556.GA6086@quack2.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210219101556.GA6086@quack2.suse.cz> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Fri 19-02-21 11:15:56, Jan Kara wrote: > On Thu 18-02-21 14:35:39, Amir Goldstein wrote: > > On Thu, Feb 18, 2021 at 1:15 PM Jan Kara wrote: > > > > > > On Thu 18-02-21 12:56:18, Amir Goldstein wrote: > > > > On Wed, Feb 17, 2021 at 1:25 PM Jan Kara wrote: > > > > > > > > > > On Wed 17-02-21 12:52:21, Amir Goldstein wrote: > > > > > > On Tue, Feb 16, 2021 at 6:02 PM Jan Kara wrote: > > > > > > > > > > > > > > Hi Amir! > > > > > > > > > > > > > > Looking at the patches I've got one idea: > > > > > > > > > > > > > > Currently you have fsnotify_event like: > > > > > > > > > > > > > > struct fsnotify_event { > > > > > > > struct list_head list; > > > > > > > unsigned int key; > > > > > > > unsigned int next_bucket; > > > > > > > }; > > > > > > > > > > > > > > And 'list' is used for hashed queue list, next_bucket is used to simulate > > > > > > > single queue out of all the individual lists. The option I'm considering > > > > > > > is: > > > > > > > > > > > > > > struct fsnotify_event { > > > > > > > struct list_head list; > > > > > > > struct fsnotify_event *hash_next; > > > > > > > unsigned int key; > > > > > > > }; > > > > > > > > > > > > > > So 'list' would stay to be used for the single queue of events like it was > > > > > > > before your patches. 'hash_next' would be used for list of events in the > > > > > > > hash chain. The advantage of this scheme would be somewhat more obvious > > > > > > > handling, > > > > > > > > > > > > I can agree to that. > > > > > > > > > > > > > also we can handle removal of permission events (they won't be > > > > > > > hashed so there's no risk of breaking hash-chain in the middle, removal > > > > > > > from global queue is easy as currently). > > > > > > > > > > > > Ok. but I do not really see a value in hashing non-permission events > > > > > > for high priority groups, so this is not a strong argument. > > > > > > > > > > The reason why I thought it is somewhat beneficial is that someone might be > > > > > using higher priority fanotify group just for watching non-permission > > > > > events because so far the group priority makes little difference. And > > > > > conceptually it isn't obvious (from userspace POV) why higher priority > > > > > groups should be merging events less efficiently... > > > > > > > > > > > > > So I implemented your suggestion with ->next_event, but it did not > > > > end up with being able to remove from the middle of the queue. > > > > The thing is we know that permission events are on list #0, but what > > > > we need to find out when removing a permission event is the previous > > > > event in timeline order and we do not have that information. > > > > > > So my idea was that if 'list' is the time ordered list and permission > > > events are *never inserted into the hash* (we don't need them there as > > > hashed lists are used only for merging), then removal of permission events > > > is no problem. > > > > We are still not talking in the same language. > > Yes, I think so :). > > > I think what you mean is use a dedicated list only for permission events > > which is not any one of the hash lists. > > > > In that case, get_one_event() will have to look at both the high > > priority queue and the hash queue if we want to allow mixing hashed > > event with permission events. > > > > It will also mean that permission events always get priority over non-permission > > events. While this makes a lot of sense, this is not the current behavior. > > > > So what am I missing? > > Let me explain with the pseudocode. fsnotify_add_event() will do: > > spin_lock(&group->notification_lock); > ... > if (!list_empty(list) && merge) { > ret = merge(list, event); > if (ret) > bail > } > group->q_len++; > list_add_tail(&event->list, &group->notification_list); > if (add_hash) { > /* Add to merge hash */ > *(group->merge_hash[hash(event->key)]->lastp) = event; > group->merge_hash[hash(event->key)]->lastp = &(event->hash_next); > } > spin_unlock(&group->notification_lock); > > And we set 'add_hash' to true only for non-permission events. The merge() > function can use merge_hash[] to speedup the search for merge candidates. > There will be no changes to fsnotify_peek_first_event() (modulo cleanups) > compared to current upstream. fsnotify_remove_queued_event() needs to > update ->first and ->lastp pointers in merge_hash[]. So something like: > > list_del_init(&event->list); > group->q_len--; > group->merge_hash[hash(event->key)]->first = event->next_hash; Actually we must do hash handling only if the event was added to the hash. So either fsnotify_remove_queued_event() needs to take an argument whether it should add event to a hash or we need to somehow identify that based on ->key having special value or checking group->merge_hash[hash(event->key)]->first == event Honza > if (!event->next_hash) { > group->merge_hash[hash(event->key)]->lastp = > &(group->merge_hash[hash(event->key)]->first); > } > > Clearer now? > Honza > -- > Jan Kara > SUSE Labs, CR -- Jan Kara SUSE Labs, CR