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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id ECD2DC7EE23 for ; Thu, 1 Jun 2023 08:43:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232148AbjFAInu (ORCPT ); Thu, 1 Jun 2023 04:43:50 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47738 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232048AbjFAIno (ORCPT ); Thu, 1 Jun 2023 04:43:44 -0400 Received: from out-41.mta1.migadu.com (out-41.mta1.migadu.com [IPv6:2001:41d0:203:375::29]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D3C4EFB for ; Thu, 1 Jun 2023 01:43:41 -0700 (PDT) Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1685609019; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=GrV1KM3/y3S5hBdJqzM74vPmzXw6kimHKx1fZTZGaeI=; b=D81vOtJuXcfgtNau4PafJgR+tR3LuhpfN/OgTKmkEmM+eZZJnb+fqBG1j2aMobjbEuGL/h bnnqxNLO7ovuGmBZAWSKGlfQ1ZrgInPMLp7O4m8wvHw5mM2vXYwnHDdUwuTRZHp32SWOW/ 0esYzjRYjctiv6T19eWTOTn0tmnh7eQ= Date: Thu, 1 Jun 2023 16:43:32 +0800 MIME-Version: 1.0 Subject: Re: [PATCH 6/8] xfs: introduce xfs_fs_destroy_super() Content-Language: en-US To: Dave Chinner Cc: akpm@linux-foundation.org, tkhai@ya.ru, roman.gushchin@linux.dev, vbabka@suse.cz, viro@zeniv.linux.org.uk, brauner@kernel.org, djwong@kernel.org, hughd@google.com, paulmck@kernel.org, muchun.song@linux.dev, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org, linux-kernel@vger.kernel.org, Qi Zheng References: <20230531095742.2480623-1-qi.zheng@linux.dev> <20230531095742.2480623-7-qi.zheng@linux.dev> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Qi Zheng In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Dave, On 2023/6/1 07:48, Dave Chinner wrote: > On Wed, May 31, 2023 at 09:57:40AM +0000, Qi Zheng wrote: >> From: Kirill Tkhai >> >> xfs_fs_nr_cached_objects() touches sb->s_fs_info, >> and this patch makes it to be destructed later. >> >> After this patch xfs_fs_nr_cached_objects() is safe >> for splitting unregister_shrinker(): mp->m_perag_tree >> is stable till destroy_super_work(), while iteration >> over it is already RCU-protected by internal XFS >> business. >> >> Signed-off-by: Kirill Tkhai >> Signed-off-by: Qi Zheng >> --- >> fs/xfs/xfs_super.c | 25 ++++++++++++++++++++++--- >> 1 file changed, 22 insertions(+), 3 deletions(-) >> >> diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c >> index 7e706255f165..694616524c76 100644 >> --- a/fs/xfs/xfs_super.c >> +++ b/fs/xfs/xfs_super.c >> @@ -743,11 +743,18 @@ xfs_fs_drop_inode( >> } >> >> static void >> -xfs_mount_free( >> +xfs_free_names( >> struct xfs_mount *mp) >> { >> kfree(mp->m_rtname); >> kfree(mp->m_logname); >> +} >> + >> +static void >> +xfs_mount_free( >> + struct xfs_mount *mp) >> +{ >> + xfs_free_names(mp); >> kmem_free(mp); >> } >> >> @@ -1136,8 +1143,19 @@ xfs_fs_put_super( >> xfs_destroy_mount_workqueues(mp); >> xfs_close_devices(mp); >> >> - sb->s_fs_info = NULL; >> - xfs_mount_free(mp); >> + xfs_free_names(mp); >> +} >> + >> +static void >> +xfs_fs_destroy_super( >> + struct super_block *sb) >> +{ >> + if (sb->s_fs_info) { >> + struct xfs_mount *mp = XFS_M(sb); >> + >> + kmem_free(mp); >> + sb->s_fs_info = NULL; >> + } >> } >> >> static long >> @@ -1165,6 +1183,7 @@ static const struct super_operations xfs_super_operations = { >> .dirty_inode = xfs_fs_dirty_inode, >> .drop_inode = xfs_fs_drop_inode, >> .put_super = xfs_fs_put_super, >> + .destroy_super = xfs_fs_destroy_super, >> .sync_fs = xfs_fs_sync_fs, >> .freeze_fs = xfs_fs_freeze, >> .unfreeze_fs = xfs_fs_unfreeze, > > I don't really like this ->destroy_super() callback, especially as > it's completely undocumented as to why it exists. This is purely a > work-around for handling extended filesystem superblock shrinker > functionality, yet there's nothing that tells the reader this. > > It also seems to imply that the superblock shrinker can continue to > run after the existing unregister_shrinker() call before ->kill_sb() > is called. This violates the assumption made in filesystems that the > superblock shrinkers have been stopped and will never run again > before ->kill_sb() is called. Hence ->kill_sb() implementations > assume there is nothing else accessing filesystem owned structures > and it can tear down internal structures safely. > > Realistically, the days of XFS using this superblock shrinker > extension are numbered. We've got a lot of the infrastructure we > need in place to get rid of the background inode reclaim > infrastructure that requires this shrinker extension, and it's on my > list of things that need to be addressed in the near future. > > In fact, now that I look at it, I think the shmem usage of this > superblock shrinker interface is broken - it returns SHRINK_STOP to > ->free_cached_objects(), but the only valid return value is the > number of objects freed (i.e. 0 is nothing freed). These special > superblock extension interfaces do not work like a normal > shrinker.... > > Hence I think the shmem usage should be replaced with an separate > internal shmem shrinker that is managed by the filesystem itself > (similar to how XFS has multiple internal shrinkers). > > At this point, then the only user of this interface is (again) XFS. > Given this, adding new VFS methods for a single filesystem > for functionality that is planned to be removed is probably not the > best approach to solving the problem. Thanks for such a detailed analysis. Kirill Tkhai just proposeed a new method[1], I cc'd you on the email. [1]. https://lore.kernel.org/lkml/bab60fe4-964c-43a6-ecce-4cbd4981d875@ya.ru/ Thanks, Qi > > Cheers, > > Dave.