From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-113.freemail.mail.aliyun.com (out30-113.freemail.mail.aliyun.com [115.124.30.113]) (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 00D48173347; Wed, 28 Aug 2024 11:37:35 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.113 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724845059; cv=none; b=oGgnLBOEO1ZyORCRySEzbBvOjJ0D1fuJSdz4dvAekSJPmRwW5k+cK90q7bcrOGkBAYARAE4Zgmw/G57xN6Db4Ns1aL+OtCwyx5RxXEfwL+kZYaNm+0eKWpHKVy7d2KhFrvyMTIM5EclfrrP3DmTN+jIG4EAQgMcqCwxilwKIkKk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724845059; c=relaxed/simple; bh=DayXTzJU+YhVIOAHUrAl/QSM+Bc01leTMONhVAN9SfI=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=H/Xlwl0eD4ogNWCWfrCyZsyMgC90ZQ2SvJV4HwTAW99VxFAiCB/NhVO8NpN4Kf+l6zYRWu8ZQyeCsgm0deUdqsIcDwvAx5ovQAjqVLpEjNa+ezv5VBFRcUsSg5My5w+WnioiFrCnQln0N+xrcblSLS9yl2keG/Qz60naVWmaNLM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b=txUBEcw1; arc=none smtp.client-ip=115.124.30.113 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b="txUBEcw1" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1724845047; h=Message-ID:Date:MIME-Version:Subject:To:From:Content-Type; bh=ugNMtmVRjHIn/42KzidtvoiLqJnhMfKlcNcK8/ZW6MI=; b=txUBEcw1gAX25koQZAV7ANsjuUlc1T9kA1mEoQY9d3KZjztLGGGvSnqj6YCDf7xoDNoDzTzI8ozLWE01Z4R2t3MKliLDb7+Lmv5GXvlQShIsLECA5PxNVl/Yyd9FSF0WHij+ji+RaWTvh5BvtnjyuMJnOuzT30VcvXN83mQ7miU= Received: from 30.221.147.140(mailfrom:jefflexu@linux.alibaba.com fp:SMTPD_---0WDplXqn_1724845046) by smtp.aliyun-inc.com; Wed, 28 Aug 2024 19:37:27 +0800 Message-ID: Date: Wed, 28 Aug 2024 19:37:26 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] fuse: add fast path for fuse_range_is_writeback To: yangyun Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, lixiaokeng@huawei.com, miklos@szeredi.hu References: <8e235c73-faac-4cb7-bc6a-e1eea5075cbe@linux.alibaba.com> <20240823061913.3921169-1-yangyun50@huawei.com> Content-Language: en-US From: Jingbo Xu In-Reply-To: <20240823061913.3921169-1-yangyun50@huawei.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 8/23/24 2:19 PM, yangyun wrote: > Sorry for the late reply. > > On Wed, Aug 14, 2024 at 05:56:06PM +0800, Jingbo Xu wrote: >> >> >> On 8/14/24 5:36 PM, yangyun wrote: >>> In some cases, the fi->writepages may be empty. And there is no need >>> to check fi->writepages with spin_lock, which may have an impact on >>> performance due to lock contention. For example, in scenarios where >>> multiple readers read the same file without any writers, or where >>> the page cache is not enabled. >>> >>> Also remove the outdated comment since commit 6b2fb79963fb ("fuse: >>> optimize writepages search") has optimize the situation by replacing >>> list with rb-tree. >>> >>> Signed-off-by: yangyun >>> --- >>> fs/fuse/file.c | 6 +++--- >>> 1 file changed, 3 insertions(+), 3 deletions(-) >>> >>> diff --git a/fs/fuse/file.c b/fs/fuse/file.c >>> index f39456c65ed7..59c911b61000 100644 >>> --- a/fs/fuse/file.c >>> +++ b/fs/fuse/file.c >>> @@ -448,9 +448,6 @@ static struct fuse_writepage_args *fuse_find_writeback(struct fuse_inode *fi, >>> >>> /* >>> * Check if any page in a range is under writeback >>> - * >>> - * This is currently done by walking the list of writepage requests >>> - * for the inode, which can be pretty inefficient. >>> */ >>> static bool fuse_range_is_writeback(struct inode *inode, pgoff_t idx_from, >>> pgoff_t idx_to) >>> @@ -458,6 +455,9 @@ static bool fuse_range_is_writeback(struct inode *inode, pgoff_t idx_from, >>> struct fuse_inode *fi = get_fuse_inode(inode); >>> bool found; >>> >>> + if (RB_EMPTY_ROOT(&fi->writepages)) >>> + return false; >> >> fi->lock is held when inserting wpa into fi->writepages rbtree (see >> fuse_writepage_add()). I doubt if there is race condition when checking >> if fi->writepages rbtree is empty without fi->lock held. > > The code can make sure that there are no race conditions because: > 1. For O_DIRECT and FOPEN_DIRECT_IO with fc->direct_io_allow_mmap, the `filemap_write_and_wait_range` before can make the insert operation to be happend before the check operation. > 2. For other cases, there are no pagecache operaions so the fi->writepages is always empty. > > In my usercase, the fi->writepages is usually empty but the spin_lock associated with it contributes a great impact on the performace of my filesystem due to lock contention. So optimize it. Thanks for the explanation. There are multiple callsites of fuse_wait_on_page_writeback(), and how do you ensure that there can't be any concurrent fuse_writepage_add() with these callsites. I'm not sure if the concurrency indeed makes a difference, since fuse_range_is_writeback() releases fi->lock before it returns anyway. -- Thanks, Jingbo