From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id DCCFF1C6A1 for ; Sat, 11 May 2024 18:28:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1715452139; cv=none; b=dlQiR+CZOqqeq4ZGMlaInkZFNQqCJZiyd2Ru22PileBwYIF159+y+ytBldUAUWA/VI5SUZgAhirhzO5xF2G2Ys9LrUg7Ro6uhfJJ/E64CuwdrkdTuKftnpacDjKzlz+UKxYjYhqmR/I54iBCOk+pKbQB7/GGA+0tl8qRUQWP7cw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1715452139; c=relaxed/simple; bh=eibUAkxq9Kt47etAreK1wtQN+pHMRG6FwGI3Py3WZNk=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=e3YJUnx6IAvn+8c3oLlJCcgZbeAWSPJOHddcoEBobCHuOPw6xwzgEtB8MtraLum/0/U1lC5Dwu8/zAPO/i9DXZuikH2TCaG6LzpUtvMKxdaFfMgby6DRWLTIWyy4mP5GsNcAfihtSp/VKtNpOeXiGeTnbvF/pBwSslTFJKvbkAY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=MXAynJBX; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="MXAynJBX" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 25EA1C2BBFC; Sat, 11 May 2024 18:28:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1715452138; bh=eibUAkxq9Kt47etAreK1wtQN+pHMRG6FwGI3Py3WZNk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=MXAynJBXh0BtAHfYKRa+ZEV2ACC/UuVzdNPgV4Nkax7f1agQxQSzGzEC9sSU+Kk8/ Hkmh75LXvq9kdHh6YDlMf0yGaLZ4w6vXRqH8p0yQItIdsWdGFKxZRSdG/XEPTNMYL1 nabVMuSk4kOLlUKbuX8tMuTXlqYvx/0+nkJSJWO0= From: Linus Torvalds To: torvalds@linux-foundation.org Cc: brauner@kernel.org, jack@suse.cz, laoar.shao@gmail.com, linux-fsdevel@vger.kernel.org, longman@redhat.com, viro@zeniv.linux.org.uk, walters@verbum.org, wangkai86@huawei.com, willy@infradead.org Subject: [PATCH] vfs: move dentry shrinking outside the inode lock in 'rmdir()' Date: Sat, 11 May 2024 11:26:26 -0700 Message-ID: <20240511182625.6717-2-torvalds@linux-foundation.org> X-Mailer: git-send-email 2.44.0.330.g4d18c88175 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Yafang Shao reports that he has seen loads that generate billions of negative dentries in a directory, which then when the directory is removed causes excessive latencies for other users because the dentry shrinking is done under the directory inode lock. There seems to be no actual reason for holding the inode lock any more by the time we get rid of the now uninteresting negative dentries, and it's an effect of just code layout (the shared error path). Reorganize the code trivially to just have a separate success path, which simplifies the code (since 'd_delete_notify()' is only called in the success path anyway) and makes it trivial to just move the dentry shrinking outside the inode lock. Reported-by: Yafang Shao Link: https://lore.kernel.org/all/20240511022729.35144-1-laoar.shao@gmail.com/ Cc: Al Viro Cc: Christian Brauner Cc: Jan Kara Cc: Waiman Long Cc: Matthew Wilcox Signed-off-by: Linus Torvalds --- Ok, this is the same patch, just with a commit message. And I actually am running a kernel with that patch, so it compiles and boots. Very limited testing: I created a directory with ten million negative dentries, and then did a "rmdir" in one terminal window while doing a "ls" inside that directory in another to kind of reproduce (on a smaller scale) what Yafang was reporting. The "ls" was not affected at all. But honestly, this was *ONE* single trivial test, so it's almost completely worthless. fs/namei.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/fs/namei.c b/fs/namei.c index 28e62238346e..474b1ee3266d 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -4217,16 +4217,19 @@ int vfs_rmdir(struct mnt_idmap *idmap, struct inode *dir, if (error) goto out; - shrink_dcache_parent(dentry); dentry->d_inode->i_flags |= S_DEAD; dont_mount(dentry); detach_mounts(dentry); + inode_unlock(dentry->d_inode); + + shrink_dcache_parent(dentry); + dput(dentry); + d_delete_notify(dir, dentry); + return 0; out: inode_unlock(dentry->d_inode); dput(dentry); - if (!error) - d_delete_notify(dir, dentry); return error; } EXPORT_SYMBOL(vfs_rmdir); -- 2.44.0.330.g4d18c88175