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=ham 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 82836C433B4 for ; Mon, 19 Apr 2021 07:35:18 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id D66446102A for ; Mon, 19 Apr 2021 07:35:17 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D66446102A 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 5F7206B0036; Mon, 19 Apr 2021 03:35:17 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 594396B006E; Mon, 19 Apr 2021 03:35:17 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 434B56B0070; Mon, 19 Apr 2021 03:35:17 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0135.hostedemail.com [216.40.44.135]) by kanga.kvack.org (Postfix) with ESMTP id 24F126B0036 for ; Mon, 19 Apr 2021 03:35:17 -0400 (EDT) Received: from smtpin14.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id D5EFD181AEF3C for ; Mon, 19 Apr 2021 07:35:16 +0000 (UTC) X-FDA: 78048305832.14.415F3CB Received: from szxga06-in.huawei.com (szxga06-in.huawei.com [45.249.212.32]) by imf13.hostedemail.com (Postfix) with ESMTP id 9FD29E000102 for ; Mon, 19 Apr 2021 07:35:11 +0000 (UTC) Received: from DGGEMS409-HUB.china.huawei.com (unknown [172.30.72.58]) by szxga06-in.huawei.com (SkyGuard) with ESMTP id 4FNz7b5lZCzlZ0P; Mon, 19 Apr 2021 15:33:15 +0800 (CST) Received: from [10.174.178.5] (10.174.178.5) by DGGEMS409-HUB.china.huawei.com (10.3.19.209) with Microsoft SMTP Server id 14.3.498.0; Mon, 19 Apr 2021 15:35:09 +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> <753f414f-34a1-b16a-f826-7deb2dcd4af6@huawei.com> <87czuq4uo2.fsf@yhuang6-desk1.ccr.corp.intel.com> From: Miaohe Lin Message-ID: Date: Mon, 19 Apr 2021 15:35:09 +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: <87czuq4uo2.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: rspam05 X-Rspamd-Queue-Id: 9FD29E000102 X-Stat-Signature: aqcpsujztenxh1h3mzdi3okq88ybhc1o Received-SPF: none (huawei.com>: No applicable sender policy available) receiver=imf13; identity=mailfrom; envelope-from=""; helo=szxga06-in.huawei.com; client-ip=45.249.212.32 X-HE-DKIM-Result: none/none X-HE-Tag: 1618817711-97024 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 15:09, Huang, Ying wrote: > Miaohe Lin writes: > >> 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? > > We can call percpu_ref_init() just after kvzalloc() in alloc_swap_info(). > Yes, we can do it this way. But using ref_initialized might make the code more straightforward and simple? > Best Regards, > Huang, Ying > >> 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); >>> . >>> > . >