From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailgw1.hygon.cn (unknown [101.204.27.37]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 890FD2F531F; Fri, 17 Apr 2026 06:59:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=101.204.27.37 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776409212; cv=none; b=oIErM8NQlAHMHHmywx87z+z5B/yo9yzjHYDALqj1Ntkm4d55tGMNs6VIyRf7wcrbI2Rx7xAK/se/B39GHqlzeEfMYP2+aua9pCkbpStf6qa5i0PeroXhNGzVivjl27LmYlyrCKlpZ6B/aT4WaQZGLIKxCdT2RWq0tY3YoLlayDM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776409212; c=relaxed/simple; bh=2Qm1k46QeaCwP3PmXiD2vvdZ0MLoC5zsmI9lok6yqpc=; h=Date:From:To:CC:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=iGB/uIFGXUWHW9hc9gS2JChprkghtXCkPpNsa1dep87wvKvfkq0C2n4XNyEp6H7tE7VcLb909cLsn4N4BZno9xgC4kbSE0VsPFSA2h0F4I0Wp3zUupXuRM75OREanuJ7veTECWNqHzVY5dFaJrIMUWRFFjnVWPyYdGqq6zbeueo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=hygon.cn; spf=pass smtp.mailfrom=hygon.cn; arc=none smtp.client-ip=101.204.27.37 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=hygon.cn Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=hygon.cn Received: from maildlp1.hygon.cn (unknown [127.0.0.1]) by mailgw1.hygon.cn (Postfix) with ESMTP id 4fxm355c3TzwvXZ; Fri, 17 Apr 2026 14:59:45 +0800 (CST) Received: from maildlp1.hygon.cn (unknown [172.23.18.60]) by mailgw1.hygon.cn (Postfix) with ESMTP id 4fxm342Yk4zvkdy; Fri, 17 Apr 2026 14:59:44 +0800 (CST) Received: from cncheex04.Hygon.cn (unknown [172.23.18.114]) by maildlp1.hygon.cn (Postfix) with ESMTPS id 1F23A16E2; Fri, 17 Apr 2026 14:59:44 +0800 (CST) Received: from hsj-2U-Workstation (172.19.20.61) by cncheex04.Hygon.cn (172.23.18.114) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.36; Fri, 17 Apr 2026 14:59:42 +0800 Date: Fri, 17 Apr 2026 14:59:41 +0800 From: Huang Shijie To: Mateusz Guzik CC: , , , , , , , , , , , , , , , Subject: Re: [PATCH 0/3] mm: split the file's i_mmap tree for NUMA Message-ID: References: <20260413062042.804-1-huangsj@hygon.cn> <76pfiwabdgsej6q2yxfh3efuqvsyg7mt7rvl5itzzjyhdrto5r@53viaxsackzv> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <76pfiwabdgsej6q2yxfh3efuqvsyg7mt7rvl5itzzjyhdrto5r@53viaxsackzv> X-ClientProxiedBy: cncheex06.Hygon.cn (172.23.18.116) To cncheex04.Hygon.cn (172.23.18.114) On Mon, Apr 13, 2026 at 05:33:21PM +0200, Mateusz Guzik wrote: > On Mon, Apr 13, 2026 at 02:20:39PM +0800, Huang Shijie wrote: > > In NUMA, there are maybe many NUMA nodes and many CPUs. > > For example, a Hygon's server has 12 NUMA nodes, and 384 CPUs. > > In the UnixBench tests, there is a test "execl" which tests > > the execve system call. > > > > When we test our server with "./Run -c 384 execl", > > the test result is not good enough. The i_mmap locks contended heavily on > > "libc.so" and "ld.so". For example, the i_mmap tree for "libc.so" can have > > over 6000 VMAs, all the VMAs can be in different NUMA mode. > > The insert/remove operations do not run quickly enough. > > > > patch 1 & patch 2 are try to hide the direct access of i_mmap. > > patch 3 splits the i_mmap into sibling trees, and we can get better > > performance with this patch set: > > we can get 77% performance improvement(10 times average) > > > > To my reading you kept the lock as-is and only distributed the protected > state. > > While I don't doubt the improvement, I'm confident should you take a > look at the profile you are going to find this still does not scale with > rwsem being one of the problems (there are other global locks, some of > which have experimental patches for). > > Apart from that this does nothing to help high core systems which are > all one node, which imo puts another question mark on this specific > proposal. > > Of course one may question whether a RB tree is the right choice here, > it may be the lock-protected cost can go way down with merely a better > data structure. > > Regardless of that, for actual scalability, there will be no way around > decentralazing locking around this and partitioning per some core count > (not just by numa awareness). > > Decentralizing locking is definitely possible, but I have not looked > into specifics of how problematic it is. Best case scenario it will > merely with separate locks. Worst case scenario something needs a fully > stabilized state for traversal, in that case another rw lock can be > slapped around this, creating locking order read lock -> per-subset > write lock -- this will suffer scalability due to the read locking, but > it will still scale drastically better as apart from that there will be > no serialization. In this setting the problematic consumer will write > lock the new thing to stabilize the state. For your proposal in no-numa, I hope you can create a patch set for it. I can test it in our machine. Thanks Huang Shijie