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 60BB1C433B4 for ; Mon, 19 Apr 2021 06:46:18 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id E00DB6128C for ; Mon, 19 Apr 2021 06:46:17 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E00DB6128C Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=huawei.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 77CA36B0070; Mon, 19 Apr 2021 02:46:17 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 752936B0071; Mon, 19 Apr 2021 02:46:17 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 5F40E6B0072; Mon, 19 Apr 2021 02:46:17 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0026.hostedemail.com [216.40.44.26]) by kanga.kvack.org (Postfix) with ESMTP id 4236C6B0070 for ; Mon, 19 Apr 2021 02:46:17 -0400 (EDT) Received: from smtpin29.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 00FFB181AEF39 for ; Mon, 19 Apr 2021 06:46:17 +0000 (UTC) X-FDA: 78048182394.29.84E5762 Received: from szxga04-in.huawei.com (szxga04-in.huawei.com [45.249.212.190]) by imf02.hostedemail.com (Postfix) with ESMTP id 086BD40002DE for ; Mon, 19 Apr 2021 06:45:54 +0000 (UTC) Received: from DGGEMS403-HUB.china.huawei.com (unknown [172.30.72.58]) by szxga04-in.huawei.com (SkyGuard) with ESMTP id 4FNy1s6qHrzpYBl; Mon, 19 Apr 2021 14:43:13 +0800 (CST) Received: from [10.174.178.5] (10.174.178.5) by DGGEMS403-HUB.china.huawei.com (10.3.19.203) with Microsoft SMTP Server id 14.3.498.0; Mon, 19 Apr 2021 14:46:08 +0800 Subject: Re: [PATCH v2 1/5] mm/swapfile: add percpu_ref support for swap To: "Huang, Ying" CC: , , , , , , , , , , , , References: <20210417094039.51711-1-linmiaohe@huawei.com> <20210417094039.51711-2-linmiaohe@huawei.com> <87eef7kmzw.fsf@yhuang6-desk1.ccr.corp.intel.com> From: Miaohe Lin Message-ID: <753f414f-34a1-b16a-f826-7deb2dcd4af6@huawei.com> Date: Mon, 19 Apr 2021 14:46:07 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: <87eef7kmzw.fsf@yhuang6-desk1.ccr.corp.intel.com> Content-Type: text/plain; charset="windows-1252" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.178.5] X-CFilter-Loop: Reflected X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 086BD40002DE X-Stat-Signature: 8653srwpd1o3xtzw63mk7tu64roscyfk Received-SPF: none (huawei.com>: No applicable sender policy available) receiver=imf02; identity=mailfrom; envelope-from=""; helo=szxga04-in.huawei.com; client-ip=45.249.212.190 X-HE-DKIM-Result: none/none X-HE-Tag: 1618814754-952518 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 2021/4/19 10:48, Huang, Ying wrote: > Miaohe Lin writes: > >> We will use percpu-refcount to serialize against concurrent swapoff. This >> patch adds the percpu_ref support for swap. >> >> Signed-off-by: Miaohe Lin >> --- >> include/linux/swap.h | 3 +++ >> mm/swapfile.c | 33 +++++++++++++++++++++++++++++---- >> 2 files changed, 32 insertions(+), 4 deletions(-) >> >> diff --git a/include/linux/swap.h b/include/linux/swap.h >> index 144727041e78..8be36eb58b7a 100644 >> --- a/include/linux/swap.h >> +++ b/include/linux/swap.h >> @@ -240,6 +240,7 @@ struct swap_cluster_list { >> * The in-memory structure used to track swap areas. >> */ >> struct swap_info_struct { >> + struct percpu_ref users; /* serialization against concurrent swapoff */ > > The comments aren't general enough. We use this to check whether the > swap device has been fully initialized, etc. May be something as below? > > /* indicate and keep swap device valid */ Looks good. > >> unsigned long flags; /* SWP_USED etc: see above */ >> signed short prio; /* swap priority of this type */ >> struct plist_node list; /* entry in swap_active_head */ >> @@ -260,6 +261,8 @@ struct swap_info_struct { >> struct block_device *bdev; /* swap device or bdev of swap file */ >> struct file *swap_file; /* seldom referenced */ >> unsigned int old_block_size; /* seldom referenced */ >> + bool ref_initialized; /* seldom referenced */ >> + struct completion comp; /* seldom referenced */ >> #ifdef CONFIG_FRONTSWAP >> unsigned long *frontswap_map; /* frontswap in-use, one bit per page */ >> atomic_t frontswap_pages; /* frontswap pages in-use counter */ >> diff --git a/mm/swapfile.c b/mm/swapfile.c >> index 149e77454e3c..66515a3a2824 100644 >> --- a/mm/swapfile.c >> +++ b/mm/swapfile.c >> @@ -39,6 +39,7 @@ >> #include >> #include >> #include >> +#include >> >> #include >> #include >> @@ -511,6 +512,14 @@ static void swap_discard_work(struct work_struct *work) >> spin_unlock(&si->lock); >> } >> >> +static void swap_users_ref_free(struct percpu_ref *ref) >> +{ >> + struct swap_info_struct *si; >> + >> + si = container_of(ref, struct swap_info_struct, users); >> + complete(&si->comp); >> +} >> + >> static void alloc_cluster(struct swap_info_struct *si, unsigned long idx) >> { >> struct swap_cluster_info *ci = si->cluster_info; >> @@ -2500,7 +2509,7 @@ static void enable_swap_info(struct swap_info_struct *p, int prio, >> * Guarantee swap_map, cluster_info, etc. fields are valid >> * between get/put_swap_device() if SWP_VALID bit is set >> */ >> - synchronize_rcu(); > > You cannot remove this without changing get/put_swap_device(). It's > better to squash at least PATCH 1-2. Will squash PATCH 1-2. Thanks. > >> + percpu_ref_resurrect(&p->users); >> spin_lock(&swap_lock); >> spin_lock(&p->lock); >> _enable_swap_info(p); >> @@ -2621,11 +2630,18 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile) >> p->flags &= ~SWP_VALID; /* mark swap device as invalid */ >> spin_unlock(&p->lock); >> spin_unlock(&swap_lock); >> + >> + percpu_ref_kill(&p->users); >> /* >> - * wait for swap operations protected by get/put_swap_device() >> - * to complete >> + * We need synchronize_rcu() here to protect the accessing >> + * to the swap cache data structure. >> */ >> synchronize_rcu(); >> + /* >> + * Wait for swap operations protected by get/put_swap_device() >> + * to complete. >> + */ > > I think the comments (after some revision) can be moved before > percpu_ref_kill(). The synchronize_rcu() comments can be merged. > Ok. >> + wait_for_completion(&p->comp); >> >> flush_work(&p->discard_work); >> >> @@ -3132,7 +3148,7 @@ static bool swap_discardable(struct swap_info_struct *si) >> SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags) >> { >> struct swap_info_struct *p; >> - struct filename *name; >> + struct filename *name = NULL; >> struct file *swap_file = NULL; >> struct address_space *mapping; >> int prio; >> @@ -3163,6 +3179,15 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags) >> >> INIT_WORK(&p->discard_work, swap_discard_work); >> >> + if (!p->ref_initialized) { > > I don't think it's necessary to add another flag p->ref_initialized. We > can distinguish newly allocated and reused swap_info_struct in alloc_swap_info(). > If newly allocated swap_info_struct failed to init percpu_ref, it will be considered as a reused one in alloc_swap_info() _but_ the field users of swap_info_struct is actually uninitialized. Does this make sense for you? Many Thanks for quick review. > Best Regards, > Huang, Ying > >> + error = percpu_ref_init(&p->users, swap_users_ref_free, >> + PERCPU_REF_INIT_DEAD, GFP_KERNEL); >> + if (unlikely(error)) >> + goto bad_swap; >> + init_completion(&p->comp); >> + p->ref_initialized = true; >> + } >> + >> name = getname(specialfile); >> if (IS_ERR(name)) { >> error = PTR_ERR(name); > . >