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=-13.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 065D5C433B4 for ; Mon, 19 Apr 2021 07:52:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CB98860FEF for ; Mon, 19 Apr 2021 07:52:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237758AbhDSHxF (ORCPT ); Mon, 19 Apr 2021 03:53:05 -0400 Received: from mga18.intel.com ([134.134.136.126]:22440 "EHLO mga18.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238016AbhDSHxA (ORCPT ); Mon, 19 Apr 2021 03:53:00 -0400 IronPort-SDR: ck7jXRhI7vrWNyAlF8w64sPGasZURYZofA97MxxZga5GRO+tTmwCAUq40t67+IA7/1oCXDBRRq LbQ/XG6Kzj7A== X-IronPort-AV: E=McAfee;i="6200,9189,9958"; a="182778598" X-IronPort-AV: E=Sophos;i="5.82,233,1613462400"; d="scan'208";a="182778598" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by orsmga106.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 19 Apr 2021 00:52:29 -0700 IronPort-SDR: aV2Z4O9WOrwPjQlCoFowqNOxPzwdQjkwgyafOdD3O8ZxBD9SslfQZz9D8UwpQbAQdHkmKt4fVE Qb/ERvfZtzmg== X-IronPort-AV: E=Sophos;i="5.82,233,1613462400"; d="scan'208";a="426412184" Received: from yhuang6-desk1.sh.intel.com (HELO yhuang6-desk1.ccr.corp.intel.com) ([10.239.13.1]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 19 Apr 2021 00:52:21 -0700 From: "Huang, Ying" To: Miaohe Lin Cc: , , , , , , , , , , , , Subject: Re: [PATCH v2 1/5] mm/swapfile: add percpu_ref support for swap 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> Date: Mon, 19 Apr 2021 15:52:16 +0800 In-Reply-To: (Miaohe Lin's message of "Mon, 19 Apr 2021 15:35:09 +0800") Message-ID: <87zgxu3e4v.fsf@yhuang6-desk1.ccr.corp.intel.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=ascii Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Miaohe Lin writes: > 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? I think that it's simpler to call percpu_ref_init() in alloc_swap_info(). We can just call percpu_ref_init() for allocated swap_info_struct blindly, and call percpu_ref_exit() if we reuse. Best Regards, Huang, Ying >> 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); >>>> . >>>> >> . >> 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=-13.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 AC140C433B4 for ; Mon, 19 Apr 2021 07:52:33 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 1F53F6102A for ; Mon, 19 Apr 2021 07:52:33 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1F53F6102A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 7F4FA6B0036; Mon, 19 Apr 2021 03:52:32 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 7A2F66B006E; Mon, 19 Apr 2021 03:52:32 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 61D636B0070; Mon, 19 Apr 2021 03:52:32 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0152.hostedemail.com [216.40.44.152]) by kanga.kvack.org (Postfix) with ESMTP id 435406B0036 for ; Mon, 19 Apr 2021 03:52:32 -0400 (EDT) Received: from smtpin16.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id EC761180AD838 for ; Mon, 19 Apr 2021 07:52:31 +0000 (UTC) X-FDA: 78048349302.16.400C005 Received: from mga07.intel.com (mga07.intel.com [134.134.136.100]) by imf04.hostedemail.com (Postfix) with ESMTP id 10A593C5 for ; Mon, 19 Apr 2021 07:52:28 +0000 (UTC) IronPort-SDR: AG9nNcMdwU9r0y8bIloIKDmbhz2zHX4o2y1M/9IZVe0+td9OFeifWMAXzymr+igGf0jKIUU1iw 4/0NY8GOPzVQ== X-IronPort-AV: E=McAfee;i="6200,9189,9958"; a="259242641" X-IronPort-AV: E=Sophos;i="5.82,233,1613462400"; d="scan'208";a="259242641" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by orsmga105.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 19 Apr 2021 00:52:29 -0700 IronPort-SDR: aV2Z4O9WOrwPjQlCoFowqNOxPzwdQjkwgyafOdD3O8ZxBD9SslfQZz9D8UwpQbAQdHkmKt4fVE Qb/ERvfZtzmg== X-IronPort-AV: E=Sophos;i="5.82,233,1613462400"; d="scan'208";a="426412184" Received: from yhuang6-desk1.sh.intel.com (HELO yhuang6-desk1.ccr.corp.intel.com) ([10.239.13.1]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 19 Apr 2021 00:52:21 -0700 From: "Huang, Ying" To: Miaohe Lin Cc: , , , , , , , , , , , , Subject: Re: [PATCH v2 1/5] mm/swapfile: add percpu_ref support for swap 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> Date: Mon, 19 Apr 2021 15:52:16 +0800 In-Reply-To: (Miaohe Lin's message of "Mon, 19 Apr 2021 15:35:09 +0800") Message-ID: <87zgxu3e4v.fsf@yhuang6-desk1.ccr.corp.intel.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=ascii X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 10A593C5 X-Stat-Signature: i83sw3otpnhdtu7mxda6c6zyyrr7fahx Received-SPF: none (intel.com>: No applicable sender policy available) receiver=imf04; identity=mailfrom; envelope-from=""; helo=mga07.intel.com; client-ip=134.134.136.100 X-HE-DKIM-Result: none/none X-HE-Tag: 1618818748-432003 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: Miaohe Lin writes: > 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? I think that it's simpler to call percpu_ref_init() in alloc_swap_info(). We can just call percpu_ref_init() for allocated swap_info_struct blindly, and call percpu_ref_exit() if we reuse. Best Regards, Huang, Ying >> 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); >>>> . >>>> >> . >>