From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6FA35C77B73 for ; Mon, 5 Jun 2023 21:13:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229660AbjFEVNz (ORCPT ); Mon, 5 Jun 2023 17:13:55 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38818 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230459AbjFEVNm (ORCPT ); Mon, 5 Jun 2023 17:13:42 -0400 Received: from out-58.mta0.migadu.com (out-58.mta0.migadu.com [91.218.175.58]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A0372100 for ; Mon, 5 Jun 2023 14:13:40 -0700 (PDT) Date: Mon, 5 Jun 2023 17:13:30 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1685999618; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=oI/D2KsCHwim00FnKX8JEpI3trD4/Ay4oLN6y5jMs+w=; b=Ou0t5k0wdLvYQe4I1KiKwwoZvxsvVwlNJliRyeWssvJBsu1TjLT0R5xnAEF8ghzWl5EIl9 wvjRxKwXo9+fHBI+ActLKXfymEdPx4wflBDdlUy8yktx25QJFLEuEOLWYXAN1GppOyjRcm hR70f2tpuOItMjMDbRE2yoaC4QllkuI= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Kent Overstreet To: Mike Rapoport Cc: Mark Rutland , linux-kernel@vger.kernel.org, Andrew Morton , Catalin Marinas , Christophe Leroy , "David S. Miller" , Dinh Nguyen , Heiko Carstens , Helge Deller , Huacai Chen , Luis Chamberlain , Michael Ellerman , "Naveen N. Rao" , Palmer Dabbelt , Russell King , Song Liu , Steven Rostedt , Thomas Bogendoerfer , Thomas Gleixner , Will Deacon , bpf@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mips@vger.kernel.org, linux-mm@kvack.org, linux-modules@vger.kernel.org, linux-parisc@vger.kernel.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, loongarch@lists.linux.dev, netdev@vger.kernel.org, sparclinux@vger.kernel.org, x86@kernel.org Subject: Re: [PATCH 00/13] mm: jit/text allocator Message-ID: References: <20230601101257.530867-1-rppt@kernel.org> <20230605092040.GB3460@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230605092040.GB3460@kernel.org> X-Migadu-Flow: FLOW_OUT Precedence: bulk List-ID: X-Mailing-List: linux-parisc@vger.kernel.org On Mon, Jun 05, 2023 at 12:20:40PM +0300, Mike Rapoport wrote: > On Fri, Jun 02, 2023 at 10:35:09AM +0100, Mark Rutland wrote: > > On Thu, Jun 01, 2023 at 02:14:56PM -0400, Kent Overstreet wrote: > > > On Thu, Jun 01, 2023 at 05:12:03PM +0100, Mark Rutland wrote: > > > > For a while I have wanted to give kprobes its own allocator so that it can work > > > > even with CONFIG_MODULES=n, and so that it doesn't have to waste VA space in > > > > the modules area. > > > > > > > > Given that, I think these should have their own allocator functions that can be > > > > provided independently, even if those happen to use common infrastructure. > > > > > > How much memory can kprobes conceivably use? I think we also want to try > > > to push back on combinatorial new allocators, if we can. > > > > That depends on who's using it, and how (e.g. via BPF). > > > > To be clear, I'm not necessarily asking for entirely different allocators, but > > I do thinkg that we want wrappers that can at least pass distinct start+end > > parameters to a common allocator, and for arm64's modules code I'd expect that > > we'd keep the range falblack logic out of the common allcoator, and just call > > it twice. > > > > > > > Several architectures override module_alloc() because of various > > > > > constraints where the executable memory can be located and this causes > > > > > additional obstacles for improvements of code allocation. > > > > > > > > > > This set splits code allocation from modules by introducing > > > > > jit_text_alloc(), jit_data_alloc() and jit_free() APIs, replaces call > > > > > sites of module_alloc() and module_memfree() with the new APIs and > > > > > implements core text and related allocation in a central place. > > > > > > > > > > Instead of architecture specific overrides for module_alloc(), the > > > > > architectures that require non-default behaviour for text allocation must > > > > > fill jit_alloc_params structure and implement jit_alloc_arch_params() that > > > > > returns a pointer to that structure. If an architecture does not implement > > > > > jit_alloc_arch_params(), the defaults compatible with the current > > > > > modules::module_alloc() are used. > > > > > > > > As above, I suspect that each of the callsites should probably be using common > > > > infrastructure, but I don't think that a single jit_alloc_arch_params() makes > > > > sense, since the parameters for each case may need to be distinct. > > > > > > I don't see how that follows. The whole point of function parameters is > > > that they may be different :) > > > > What I mean is that jit_alloc_arch_params() tries to aggregate common > > parameters, but they aren't actually common (e.g. the actual start+end range > > for allocation). > > jit_alloc_arch_params() tries to aggregate architecture constraints and > requirements for allocations of executable memory and this exactly what > the first 6 patches of this set do. > > A while ago Thomas suggested to use a structure that parametrizes > architecture constraints by the memory type used in modules [1] and Song > implemented the infrastructure for it and x86 part [2]. > > I liked the idea of defining parameters in a single structure, but I > thought that approaching the problem from the arch side rather than from > modules perspective will be better starting point, hence these patches. > > I don't see a fundamental reason why a single structure cannot describe > what is needed for different code allocation cases, be it modules, kprobes > or bpf. There is of course an assumption that the core allocations will be > the same for all the users, and it seems to me that something like > > * allocate physical memory if allocator caches are empty > * map it in vmalloc or modules address space > * return memory from the allocator cache to the caller > > will work for all usecases. > > We might need separate caches for different cases on different > architectures, and a way to specify what cache should be used in the > allocator API, but that does not contradict a single structure for arch > specific parameters, but only makes it more elaborate, e.g. something like > > enum jit_type { > JIT_MODULES_TEXT, > JIT_MODULES_DATA, > JIT_KPROBES, > JIT_FTRACE, > JIT_BPF, > JIT_TYPE_MAX, > }; Why would we actually need different enums for modules_text, kprobes, ftrace and bpf? Why can't we treat all text allocations the same? The reason we can't do that currently is because modules need to go in a 128Mb region on some archs, and without sub page allocation bpf/kprobes/etc. burn a full page for each allocation. But we're doing sub page allocation - right? That leaves module data - which really needs to be split out into rw, ro, ro_after_init - but I'm not sure we'd even want the same API for those, they need fairly different page permissions handling.