From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.zytor.com (terminus.zytor.com [198.137.202.136]) (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 DFE5933F582 for ; Sat, 25 Apr 2026 09:52:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.137.202.136 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777110748; cv=none; b=Kpe0XH3sDqo9m/IF9yZ35aZoM85vwM1pH9CyazZK6OvBqVDh0kM8spzS2CoZIPVdCbXIQ9bWXg2eoWsJHM2m7vD2nIlTkFCrBJVwznw442691oMM0foYPUNBlHjTUVHLgKwfmnFVFk/IKRQDlAh6uFeb+RlH6hRfGvr+biNLYL4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777110748; c=relaxed/simple; bh=ad3AN9vCPK/kaGIp15Za/ZzaOfrk5JV8oeJyxGM04BA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Jq86SBNE9B7HWR612+fC4xFJu0i+61Kk+ieJEAmVnzKEpeDExxFXv33gME+Xjn73ZPywTq0e4pZP3Hhx9TKhsjQgdPBf7gjwRXy3N6LJPrrHavhybJvbPCRIkN+qm/uMadNdpde22GqJnOAQbuPfk/xyKmeH+0TNpiur0b2bFYQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zytor.com; spf=pass smtp.mailfrom=zytor.com; dkim=pass (2048-bit key) header.d=zytor.com header.i=@zytor.com header.b=Vq9nQMq4; arc=none smtp.client-ip=198.137.202.136 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zytor.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=zytor.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=zytor.com header.i=@zytor.com header.b="Vq9nQMq4" Received: from [IPV6:2601:646:8085:1a81:cb3a:9fd0:def5:1007] ([IPv6:2601:646:8085:1a81:cb3a:9fd0:def5:1007]) (authenticated bits=0) by mail.zytor.com (8.18.1/8.17.1) with ESMTPSA id 63P9JaV7911354 (version=TLSv1.3 cipher=TLS_AES_128_GCM_SHA256 bits=128 verify=NO); Sat, 25 Apr 2026 02:19:36 -0700 DKIM-Filter: OpenDKIM Filter v2.11.0 mail.zytor.com 63P9JaV7911354 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zytor.com; s=2026032601; t=1777108779; bh=vhvYVy2+fkh/jv+3V2pLBqAm1atXD9hJChgcrEaqFKw=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=Vq9nQMq4kfTp+Ig7AH43pPk9xHx4vM1reSBisRaZOk0XgF/w6ztm9SmpOMJYgh5mo 5emme67gaB/t2CpO/AxyVfbFoYal6m0gJVTTBuYhEqca+BhmIcA6nqCs7R5cWtZv5X Ia96Dc2+fcqCUgSz/2xnTgxr0gIyQ7uGp0brObF5kNwCNyRHeG5lGnfknU2c9lvuKk LD3D6ap07frG4zWBubO6LGJTSQXk3v5KNxVcleMddkDqBIeh7s+enQqF7ue9thOY9Y CbVGFsQ4RHuxr2DgvW2NmUcqnoH9BkD9Bpp/7PuIOZVHQPhuDf05jv689sY4/MwsY+ Sh/r4QupXDlJg== Message-ID: <6369e5ce-74e3-4c68-8053-d7d7d21b6955@zytor.com> Date: Sat, 25 Apr 2026 02:19:30 -0700 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 v2 00/13] Dynamic Kernel Stacks To: Dave Hansen , David Stevens , Pasha Tatashin , Linus Walleij , Will Deacon , Quentin Perret , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, Andy Lutomirski , Xin Li , Peter Zijlstra , Andrew Morton , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Uladzislau Rezki , Kees Cook Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20260424191456.2679717-1-stevensd@google.com> Content-Language: en-US, sv-SE From: "H. Peter Anvin" In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 2026-04-24 12:41, Dave Hansen wrote: > On 4/24/26 12:14, David Stevens wrote: >> The question is then: is this approach something that is fundamentally >> untenable in the kernel > > Yes. Fundamentally untenable. > > Not allowing stack faults has been a wonderful simplification. It's one > of those things that just plain makes the kernel easier to maintain. > Saving low single digits of system memory is not exactly making me eager > to go back to the harder-to-maintain days. > > I seriously doubt that this 1% is the lowest hanging fruit for memory > bloat on these systems. ;) It is worth noting that this was one of the VERY early design decisions that has shaped Linux from the beginning: - No swapping of kernel memory - Kernel stacks are statically allocated - Physical RAM is mapped into the kernel at all times - A "monolithic" kernel using function calls, not message passing - A kernel interface that closely maps to the low-level application API (e.g. each user space thread is a kernel thread.) - Kernel ABIs and APIs are subject to evolution; stability is only guaranteed in user space. Those design decisions are, by and large, what has made Linux Linux: a relatively simple, highly performant, and reliable system. -hpa