From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-m32107.qiye.163.com (mail-m32107.qiye.163.com [220.197.32.107]) (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 8C0DF4315F for ; Thu, 30 Apr 2026 06:06:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=220.197.32.107 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777529180; cv=none; b=Ycz43G1RkJN0RdCklqPYDpHsf2Jlghg7+oj0pyz56dZJECgzWsvKFS161sBudnGNruTuBo+XROycsYVpxpiHpRX3ARajdf8/7GwmcXe21Hhh21k95bt9tUVMSr+T5H0fRY12Tr1QK6AIvrd4uiqh+oIYdhZOIgLh3N8b8WkCrZ8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777529180; c=relaxed/simple; bh=8OTnlwuA+T7ASw03lwXLFwwhiEwmE+0JJXlenDJzjIs=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ovB1aVsF8P0CyqVgCXNLE6XEttIEaWa2EB8M8xEEbl28mjNOKUtRUHC8OzDZYCgwggNNpZrR4zTVusljVzrVF9CwH7R07mjwjmrhbok3x5BxZ/sU13SbzhfbPaRK6/bLGDIrF6sm46b+bLl4YSylWD9ZuckIxk/nrAIDtRw7ZFo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=easystack.cn; spf=pass smtp.mailfrom=easystack.cn; arc=none smtp.client-ip=220.197.32.107 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=easystack.cn Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=easystack.cn Received: from [192.168.0.18] (unknown [218.94.118.90]) by smtp.qiye.163.com (Hmail) with ESMTP id 199470a92; Thu, 30 Apr 2026 14:00:55 +0800 (GMT+08:00) Message-ID: <984f08b3-e29a-46b4-97c7-a31a7fdb34f4@easystack.cn> Date: Thu, 30 Apr 2026 14:00:54 +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 v3 3/4] mm/page_owner: add NUMA node filter with nodelist support To: SeongJae Park Cc: akpm@linux-foundation.org, vbabka@kernel.org, surenb@google.com, mhocko@suse.com, jackmanb@google.com, hannes@cmpxchg.org, ziy@nvidia.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260430051629.78237-1-sj@kernel.org> From: "zhen.ni" In-Reply-To: <20260430051629.78237-1-sj@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-HM-Tid: 0a9ddcf9da980229kunm439aa7e31f60c2 X-HM-MType: 1 X-HM-Spam-Status: e1kfGhgUHx5ZQUpXWQgPGg8OCBgUHx5ZQUlOS1dZFg8aDwILHllBWSg2Ly tZV1koWUFJQjdXWRgWCB1ZQUpXWS1ZQUlXWQ8JGhUIEh9ZQVkaSU9PVh1DHU1JHkJLTExNTlYVFA kWGhdVGRETFhoSFyQUDg9ZV1kYEgtZQVlJSkNVQk9VSkpDVUJLWVdZFhoPEhUdFFlBWU9LSFVCQk lOS1VKS0tVSkJLQlkG 在 2026/4/30 13:16, SeongJae Park 写道: > On Thu, 30 Apr 2026 11:56:33 +0800 "zhen.ni" wrote: > >> >> >> 在 2026/4/29 22:56, SeongJae Park 写道: >>> On Wed, 29 Apr 2026 17:03:56 +0800 "zhen.ni" wrote: >>> >>>> >>>> >>>> 在 2026/4/29 09:28, SeongJae Park 写道: >>>>> On Tue, 28 Apr 2026 15:11:11 +0800 Zhen Ni wrote: >>> [...] >>>>>> @@ -685,6 +685,7 @@ read_page_owner(struct file *file, char __user *buf, size_t count, loff_t *ppos) >>>>>> struct page_ext *page_ext; >>>>>> struct page_owner *page_owner; >>>>>> depot_stack_handle_t handle; >>>>>> + nodemask_t mask; >>>>>> >>>>>> if (!static_branch_unlikely(&page_owner_inited)) >>>>>> return -EINVAL; >>>>>> @@ -698,6 +699,8 @@ read_page_owner(struct file *file, char __user *buf, size_t count, loff_t *ppos) >>>>>> while (!pfn_valid(pfn) && (pfn & (MAX_ORDER_NR_PAGES - 1)) != 0) >>>>>> pfn++; >>>>>> >>>>>> + mask = owner_filter.nid_mask; >>>>>> + >>>>> >>>>> READ_ONCE() was used for owner_filter.print_mode. Should nid_mask also read >>>>> using READ_ONCE()? >>>>> >>>> The reason is that `owner_filter.nid_mask` is a nodemask_t, which is a >>>> 128-byte structure. READ_ONCE() only supports types up to 8 bytes and >>>> will trigger a compile-time assertion failure for larger structures. >>>> >>>> This was actually an issue in v2 - the AI review tool (sashiko.dev) and >>>> Andrew both caught the compilation error with READ_ONCE/WRITE_ONCE on >>>> nodemask_t, so v3 removed them. >>> >>> Thank you for kindly sharing the context. Now I understand why READ_ONCE() >>> cannot be used. But, is plain load/store safe enough for nodemask_t? >>> Shouldn't it still be protected against races? >>> >> Concurrency Safety: >> I considered spinlock and RCU, but decided against them: >> >> - Spinlock: Adds overhead on every read, overkill for a debug facility >> - RCU: Requires dynamic allocation of 128-byte nodemask_t, too complex >> - READ_ONCE/WRITE_ONCE: Not possible, exceeds 8-byte limit >> >> Plain load/store is safe here because: >> 1. page_owner is debug code with low-frequency filter changes >> 2. Worst case of torn read is temporary inconsistency in debug output >> 3. Similar debugfs interfaces use the same approach >> >> The overhead of locking doesn't justify the benefit for this debug use case. >> >> Do you think this is acceptable, or would you prefer I add locking? > > Thank you for kindly explaining this. Unless others have different opinions, I > think this is ok. But, I think this would be good to be clarly documented, on > the code or the user documentation. > I'll add a comment in the code explaining the concurrency consideration > [...] >>>>>> + /* Support: "-1" to clear, or nodelist format like "0", "0,2", "0-3" */ >>>>>> + if (kstrtoint(kbuf, 10, &val) == 0 && val == -1) >>>>>> + nodes_clear(mask); >>>>>> + else if (nodelist_parse(kbuf, mask)) { >>>>>> + ret = -EINVAL; >>>>>> + goto out_free; >>>>>> + } >>>>> >>>>> Doesn't empty string input to nodelist_parse() clears the mask? Can't it be >>>>> reused? >>>>> >>>> Yes, empty input (echo > nid) works because nodelist_parse() handles it >>>> correctly. However, nodelist_parse() - which is implemented via >>>> bitmap_parselist() - cannot handle "-1" as it's not a valid range format >>>> and would return an error. The explicit "-1" check is necessary to >>>> support `echo "-1" > nid` without returning an error. >>>> >>>> So the "-1" check handles a case that nodelist_parse() cannot handle. >>> >>> Thank you for kindly explaining the reason. But, do we really need to support >>> "-1" input? Couldn't we just redefine the interface? >>> >> I chose "-1" to clearly differentiate from valid NUMA node IDs (0, 1, 2, >> 3...).Since node IDs are non-negative integers, "-1" naturally means >> "invalid" or "no filter", which is an intuitive convention in Linux >> (e.g., pid -1, signal -1). >> >> Do you have a better suggestion for how to represent "clear filter"？ > > Seems my suggestion was too implicit. I'm suggesting using empty string > instead of "-1". I think it is also clarly differentiated from valid NUMA node > IDs? > I understand your point about simplifying the code by removing the "-1" special case. I'll remove it and use only empty string for clearing the filter. Thank you for the suggestions. > > Thanks, > SJ > > [...] > > Thanks, Zhen