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=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=unavailable 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 E7BDFC433FE for ; Fri, 4 Dec 2020 16:20:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A0D7122955 for ; Fri, 4 Dec 2020 16:20:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730404AbgLDQUR (ORCPT ); Fri, 4 Dec 2020 11:20:17 -0500 Received: from mx2.suse.de ([195.135.220.15]:40784 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726102AbgLDQUR (ORCPT ); Fri, 4 Dec 2020 11:20:17 -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 E23D3ACC4; Fri, 4 Dec 2020 16:19:35 +0000 (UTC) Subject: Re: [PATCH v2] mm: fix a race on nr_swap_pages To: Zhaoyang Huang , Zhaoyang Huang , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <1607050340-4535-1-git-send-email-zhaoyang.huang@unisoc.com> From: Vlastimil Babka Message-ID: <56407d04-2178-8a0e-ae1b-a1a4b9d7912a@suse.cz> Date: Fri, 4 Dec 2020 17:19:35 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.5.0 MIME-Version: 1.0 In-Reply-To: <1607050340-4535-1-git-send-email-zhaoyang.huang@unisoc.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/4/20 3:52 AM, Zhaoyang Huang wrote: > The scenario on which "Free swap = -4kB" happens in my system, which is caused > by several get_swap_pages racing with each other and show_swap_cache_info > happens simutaniously. No need to add a lock on get_swap_page_of_type as we > remove "Presub/PosAdd" here. > > ProcessA ProcessB ProcessC > ngoals = 1 ngoals = 1 > avail = nr_swap_pages(1) avail = nr_swap_pages(1) > nr_swap_pages(1) -= ngoals > nr_swap_pages(0) -= ngoals > nr_swap_pages = -1 > > Signed-off-by: Zhaoyang Huang Better now. Acked-by: Vlastimil Babka > --- > change of v2: fix bug of unpaired of spin_lock > --- > --- > mm/swapfile.c | 11 ++++++----- > 1 file changed, 6 insertions(+), 5 deletions(-) > > diff --git a/mm/swapfile.c b/mm/swapfile.c > index cf63b5f..1212f17 100644 > --- a/mm/swapfile.c > +++ b/mm/swapfile.c > @@ -974,9 +974,13 @@ int get_swap_pages(int n_goal, swp_entry_t swp_entries[], int entry_size) > /* Only single cluster request supported */ > WARN_ON_ONCE(n_goal > 1 && size == SWAPFILE_CLUSTER); > > + spin_lock(&swap_avail_lock); > + > avail_pgs = atomic_long_read(&nr_swap_pages) / size; > - if (avail_pgs <= 0) > + if (avail_pgs <= 0) { > + spin_unlock(&swap_avail_lock); > goto noswap; > + } > > if (n_goal > SWAP_BATCH) > n_goal = SWAP_BATCH; > @@ -986,8 +990,6 @@ int get_swap_pages(int n_goal, swp_entry_t swp_entries[], int entry_size) > > atomic_long_sub(n_goal * size, &nr_swap_pages); > > - spin_lock(&swap_avail_lock); > - > start_over: > node = numa_node_id(); > plist_for_each_entry_safe(si, next, &swap_avail_heads[node], avail_lists[node]) { > @@ -1061,14 +1063,13 @@ swp_entry_t get_swap_page_of_type(int type) > > spin_lock(&si->lock); > if (si->flags & SWP_WRITEOK) { > - atomic_long_dec(&nr_swap_pages); > /* This is called for allocating swap entry, not cache */ > offset = scan_swap_map(si, 1); > if (offset) { > + atomic_long_dec(&nr_swap_pages); > spin_unlock(&si->lock); > return swp_entry(type, offset); > } > - atomic_long_inc(&nr_swap_pages); > } > spin_unlock(&si->lock); > fail: >