From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-98.freemail.mail.aliyun.com (out30-98.freemail.mail.aliyun.com [115.124.30.98]) (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 6B95329DB65; Mon, 26 Jan 2026 12:02:35 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.98 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769428959; cv=none; b=E8tpB+JHXXGH9ROE2AsBbBeFHzYALLAOH7ni6vkW8lLBZCsTXymmoaG05KMb9wpuuY1VjP8Oz0qP+WDOQ0bsjyvJbplkm3DIudtv8v0/dIGUTCGU2wi9LFZm+OwF5plDzvTeNpSRnAuK/P8PbJHrXRAAYWKa3cqDH16qjdOCQhc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769428959; c=relaxed/simple; bh=1ejtWTPxC7QhHvmJf8Z6FrtDXKg5bPC5ZA2RhQSYSfU=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=XltjkHzefBz8NZ78nn7/+/xVk2yG2OWb7F0sBvdoErHaNchDuRLnGVBiWTEhYxFi6hZfT7kQGXQIlNqPmOCiPaSzteMtDBCa5ridxMx8b6dQaeYuKsdOW6HXvxWfmaGABfvrocf9cqk+7kEN4Vw/TSS0Y80G7dFYXSHgAQOvaoc= 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=wKDDG/mK; arc=none smtp.client-ip=115.124.30.98 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="wKDDG/mK" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1769428947; h=Date:From:To:Subject:Message-ID:MIME-Version:Content-Type; bh=Hc/TS0tY4HUOfWDij4WQGV+0xonDLwbrony8b89dCv8=; b=wKDDG/mKMb9rg1cLvtpdeRV6Ej+XS4VU9btC3v9XsSKFdLVhqEG+t93h7q1K7L1/Wg7whOH5s81CgVK5ykmsa2qmEorvV09GLh9AwykleuNC66DIgUwHYrIFTaWqOPdfNe2X+Vx6/sHQEK+eYSzBRhG/g+pRF1dHlE2VzZPhOtU= Received: from localhost(mailfrom:alibuda@linux.alibaba.com fp:SMTPD_---0Wxu-mhe_1769428946 cluster:ay36) by smtp.aliyun-inc.com; Mon, 26 Jan 2026 20:02:26 +0800 Date: Mon, 26 Jan 2026 20:02:26 +0800 From: "D. Wythe" To: Uladzislau Rezki Cc: "D. Wythe" , "David S. Miller" , Andrew Morton , Dust Li , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Sidraya Jayagond , Wenjia Zhang , Mahanta Jambigi , Simon Horman , Tony Lu , Wen Gu , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-rdma@vger.kernel.org, linux-s390@vger.kernel.org, netdev@vger.kernel.org, oliver.yang@linux.alibaba.com Subject: Re: [PATCH net-next 2/3] mm: vmalloc: export find_vm_area() Message-ID: <20260126120226.GA6424@j66a10360.sqa.eu95> References: <20260123082349.42663-1-alibuda@linux.alibaba.com> <20260123082349.42663-3-alibuda@linux.alibaba.com> <20260124093505.GA98529@j66a10360.sqa.eu95> <20260124145754.GA57116@j66a10360.sqa.eu95> Precedence: bulk X-Mailing-List: netdev@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: User-Agent: Mutt/1.5.21 (2010-09-15) On Mon, Jan 26, 2026 at 11:28:46AM +0100, Uladzislau Rezki wrote: > Hello, D. Wythe! > > > > > On Fri, Jan 23, 2026 at 07:55:17PM +0100, Uladzislau Rezki wrote: > > > > > On Fri, Jan 23, 2026 at 04:23:48PM +0800, D. Wythe wrote: > > > > > > find_vm_area() provides a way to find the vm_struct associated with a > > > > > > virtual address. Export this symbol to modules so that modularized > > > > > > subsystems can perform lookups on vmalloc addresses. > > > > > > > > > > > > Signed-off-by: D. Wythe > > > > > > --- > > > > > > mm/vmalloc.c | 1 + > > > > > > 1 file changed, 1 insertion(+) > > > > > > > > > > > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > > > > > > index ecbac900c35f..3eb9fe761c34 100644 > > > > > > --- a/mm/vmalloc.c > > > > > > +++ b/mm/vmalloc.c > > > > > > @@ -3292,6 +3292,7 @@ struct vm_struct *find_vm_area(const void *addr) > > > > > > > > > > > > return va->vm; > > > > > > } > > > > > > +EXPORT_SYMBOL_GPL(find_vm_area); > > > > > > > > > > > This is internal. We can not just export it. > > > > > > > > > > -- > > > > > Uladzislau Rezki > > > > > > > > Hi Uladzislau, > > > > > > > > Thank you for the feedback. I agree that we should avoid exposing > > > > internal implementation details like struct vm_struct to external > > > > subsystems. > > > > > > > > Following Christoph's suggestion, I'm planning to encapsulate the page > > > > order lookup into a minimal helper instead: > > > > > > > > unsigned int vmalloc_page_order(const void *addr){ > > > > struct vm_struct *vm; > > > > vm = find_vm_area(addr); > > > > return vm ? vm->page_order : 0; > > > > } > > > > EXPORT_SYMBOL_GPL(vmalloc_page_order); > > > > > > > > Does this approach look reasonable to you? It would keep the vm_struct > > > > layout private while satisfying the optimization needs of SMC. > > > > > > > Could you please clarify why you need info about page_order? I have not > > > looked at your second patch. > > > > > > Thanks! > > > > > > -- > > > Uladzislau Rezki > > > > Hi Uladzislau, > > > > This stems from optimizing memory registration in SMC-R. To provide the > > RDMA hardware with direct access to memory buffers, we must register > > them with the NIC. During this process, the hardware generates one MTT > > entry for each physically contiguous block. Since these hardware entries > > are a finite and scarce resource, and SMC currently defaults to a 4KB > > registration granularity, a single 2MB buffer consumes 512 entries. In > > high-concurrency scenarios, this inefficiency quickly exhausts NIC > > resources and becomes a major bottleneck for system scalability. > > > > To address this, we intend to use vmalloc_huge(). When it successfully > > allocates high-order pages, the vmalloc area is backed by a sequence of > > physically contiguous chunks (e.g., 2MB each). If we know this > > page_order, we can register these larger physical blocks instead of > > individual 4KB pages, reducing MTT consumption from 512 entries down to > > 1 for every 2MB of memory (with page_order == 9). > > > > However, the result of vmalloc_huge() is currently opaque to the caller. > > We cannot determine whether it successfully allocated huge pages or fell > > back to 4KB pages based solely on the returned pointer. Therefore, we > > need a helper function to query the actual page order, enabling SMC-R to > > adapt its registration logic to the underlying physical layout. > > > > I hope this clarifies our design motivation! > > > Appreciate for the explanation. Yes it clarifies an intention. > > As for proposed patch above: > > - A page_order is available if CONFIG_HAVE_ARCH_HUGE_VMALLOC is defined; > - It makes sense to get a node, grab a spin-lock and find VM, save > page_order and release the lock. > > You can have a look at the vmalloc_dump_obj(void *object) function. > We try-spinlock there whereas you need just spin-lock. But the idea > is the same. > > -- > Uladzislau Rezki Hi Uladzislau, Thanks very much for the detailed guidance, especially on the correct locking pattern. This is extremely helpful.I will follow it and send a v2 patch series with the new helper implemented in mm/vmalloc.c. Thanks again for your support. Best regards, D. Wythe