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 2B466C433ED for ; Mon, 19 Apr 2021 02:49:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0D7A4610CA for ; Mon, 19 Apr 2021 02:49:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237317AbhDSCt2 (ORCPT ); Sun, 18 Apr 2021 22:49:28 -0400 Received: from mga01.intel.com ([192.55.52.88]:3579 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233117AbhDSCt0 (ORCPT ); Sun, 18 Apr 2021 22:49:26 -0400 IronPort-SDR: WaeUFKsaVvB/ZlJFr466mLQJuCdvGEotdSJtFvVDLua4T1ApJ+h6KpCB+MfsAmTl8VDXP6T6Bd p3BuZbvyY1nw== X-IronPort-AV: E=McAfee;i="6200,9189,9958"; a="215835621" X-IronPort-AV: E=Sophos;i="5.82,233,1613462400"; d="scan'208";a="215835621" Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by fmsmga101.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 Apr 2021 19:48:57 -0700 IronPort-SDR: W2sWlM4mursE27JiUnPo31H7itctvqNXGGJpYdix2nRklfigoroApjFupaCIo/qYpqTnIGDZih lkr49vI1XinA== X-IronPort-AV: E=Sophos;i="5.82,232,1613462400"; d="scan'208";a="419830628" Received: from yhuang6-desk1.sh.intel.com (HELO yhuang6-desk1.ccr.corp.intel.com) ([10.239.13.1]) by fmsmga008-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 Apr 2021 19:48:53 -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> Date: Mon, 19 Apr 2021 10:48:51 +0800 In-Reply-To: <20210417094039.51711-2-linmiaohe@huawei.com> (Miaohe Lin's message of "Sat, 17 Apr 2021 05:40:35 -0400") Message-ID: <87eef7kmzw.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: > 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 */ > 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. > + 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. > + 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(). 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=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 CE3ADC433B4 for ; Mon, 19 Apr 2021 02:49:01 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 7A62060E0B for ; Mon, 19 Apr 2021 02:49:01 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7A62060E0B 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 04A406B0036; Sun, 18 Apr 2021 22:49:01 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id F3CBB6B006E; Sun, 18 Apr 2021 22:49:00 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id DDD506B0070; Sun, 18 Apr 2021 22:49:00 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0214.hostedemail.com [216.40.44.214]) by kanga.kvack.org (Postfix) with ESMTP id C09266B0036 for ; Sun, 18 Apr 2021 22:49:00 -0400 (EDT) Received: from smtpin27.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 71FD2180AD837 for ; Mon, 19 Apr 2021 02:49:00 +0000 (UTC) X-FDA: 78047584440.27.53B3B14 Received: from mga06.intel.com (mga06.intel.com [134.134.136.31]) by imf29.hostedemail.com (Postfix) with ESMTP id 118A6D6 for ; Mon, 19 Apr 2021 02:48:56 +0000 (UTC) IronPort-SDR: na+5OnCz3qUeGecmf44UxnrNnVCueS8d8XcjG+4C3fTdVicBFFZ4wTOKDn1rLVO5ElK/ogfYMP 6CYKrAo6JXCA== X-IronPort-AV: E=McAfee;i="6200,9189,9958"; a="256570264" X-IronPort-AV: E=Sophos;i="5.82,232,1613462400"; d="scan'208";a="256570264" Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by orsmga104.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 Apr 2021 19:48:57 -0700 IronPort-SDR: W2sWlM4mursE27JiUnPo31H7itctvqNXGGJpYdix2nRklfigoroApjFupaCIo/qYpqTnIGDZih lkr49vI1XinA== X-IronPort-AV: E=Sophos;i="5.82,232,1613462400"; d="scan'208";a="419830628" Received: from yhuang6-desk1.sh.intel.com (HELO yhuang6-desk1.ccr.corp.intel.com) ([10.239.13.1]) by fmsmga008-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 Apr 2021 19:48:53 -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> Date: Mon, 19 Apr 2021 10:48:51 +0800 In-Reply-To: <20210417094039.51711-2-linmiaohe@huawei.com> (Miaohe Lin's message of "Sat, 17 Apr 2021 05:40:35 -0400") Message-ID: <87eef7kmzw.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-Queue-Id: 118A6D6 X-Stat-Signature: 74onot39m64g57xzjcbm7mnxmeowdgmg X-Rspamd-Server: rspam02 Received-SPF: none (intel.com>: No applicable sender policy available) receiver=imf29; identity=mailfrom; envelope-from=""; helo=mga06.intel.com; client-ip=134.134.136.31 X-HE-DKIM-Result: none/none X-HE-Tag: 1618800536-696922 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: > 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 */ > 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. > + 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. > + 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(). 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);