From: Kent Overstreet <kent.overstreet@linux.dev>
To: Mike Rapoport <rppt@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>,
linux-kernel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Christophe Leroy <christophe.leroy@csgroup.eu>,
"David S. Miller" <davem@davemloft.net>,
Dinh Nguyen <dinguyen@kernel.org>,
Heiko Carstens <hca@linux.ibm.com>, Helge Deller <deller@gmx.de>,
Huacai Chen <chenhuacai@kernel.org>,
Luis Chamberlain <mcgrof@kernel.org>,
Michael Ellerman <mpe@ellerman.id.au>,
"Naveen N. Rao" <naveen.n.rao@linux.ibm.com>,
Palmer Dabbelt <palmer@dabbelt.com>,
Russell King <linux@armlinux.org.uk>, Song Liu <song@kernel.org>,
Steven Rostedt <rostedt@goodmis.org>,
Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
Thomas Gleixner <tglx@linutronix.de>,
Will Deacon <will@kernel.org>,
bpf@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
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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
Date: Mon, 5 Jun 2023 17:13:30 -0400 [thread overview]
Message-ID: <ZH5P+iKOnoqYjbPq@moria.home.lan> (raw)
In-Reply-To: <20230605092040.GB3460@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.
next prev parent reply other threads:[~2023-06-05 21:13 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-06-01 10:12 [PATCH 00/13] mm: jit/text allocator Mike Rapoport
2023-06-01 10:12 ` [PATCH 01/13] nios2: define virtual address space for modules Mike Rapoport
2023-06-13 22:16 ` Dinh Nguyen
2023-06-01 10:12 ` [PATCH 02/13] mm: introduce jit_text_alloc() and use it instead of module_alloc() Mike Rapoport
2023-06-01 10:12 ` [PATCH 03/13] mm/jitalloc, arch: convert simple overrides of module_alloc to jitalloc Mike Rapoport
2023-06-01 10:12 ` [PATCH 04/13] mm/jitalloc, arch: convert remaining " Mike Rapoport
2023-06-01 22:35 ` Song Liu
2023-06-01 10:12 ` [PATCH 05/13] module, jitalloc: drop module_alloc Mike Rapoport
2023-06-01 10:12 ` [PATCH 06/13] mm/jitalloc: introduce jit_data_alloc() Mike Rapoport
2023-06-01 10:12 ` [PATCH 07/13] x86/ftrace: enable dynamic ftrace without CONFIG_MODULES Mike Rapoport
2023-06-01 10:12 ` [PATCH 08/13] arch: make jitalloc setup available regardless of CONFIG_MODULES Mike Rapoport
2023-06-01 10:12 ` [PATCH 09/13] kprobes: remove dependcy on CONFIG_MODULES Mike Rapoport
2023-06-01 10:12 ` [PATCH 10/13] modules, jitalloc: prepare to allocate executable memory as ROX Mike Rapoport
2023-06-01 10:12 ` [PATCH 11/13] ftrace: Add swap_func to ftrace_process_locs() Mike Rapoport
2023-06-01 10:12 ` [PATCH 12/13] x86/jitalloc: prepare to allocate exectuatble memory as ROX Mike Rapoport
2023-06-01 10:30 ` Peter Zijlstra
2023-06-01 11:07 ` Mike Rapoport
2023-06-02 0:02 ` Song Liu
2023-06-01 17:52 ` Kent Overstreet
2023-06-01 16:54 ` Edgecombe, Rick P
2023-06-01 18:00 ` Kent Overstreet
2023-06-01 18:13 ` Edgecombe, Rick P
2023-06-01 18:38 ` Kent Overstreet
2023-06-01 20:50 ` Edgecombe, Rick P
2023-06-01 23:54 ` Nadav Amit
2023-06-05 2:52 ` Steven Rostedt
2023-06-05 8:11 ` Mike Rapoport
2023-06-05 16:10 ` Edgecombe, Rick P
2023-06-05 20:42 ` Mike Rapoport
2023-06-05 21:01 ` Edgecombe, Rick P
2023-06-05 21:11 ` Nadav Amit
2023-06-04 21:47 ` Kent Overstreet
2023-06-01 22:49 ` Song Liu
2023-06-01 10:12 ` [PATCH 13/13] x86/jitalloc: make memory allocated for code ROX Mike Rapoport
2023-06-01 16:12 ` [PATCH 00/13] mm: jit/text allocator Mark Rutland
2023-06-01 18:14 ` Kent Overstreet
2023-06-02 9:35 ` Mark Rutland
2023-06-02 18:20 ` Song Liu
2023-06-03 21:11 ` Puranjay Mohan
2023-06-04 18:02 ` Kent Overstreet
2023-06-04 21:22 ` Song Liu
2023-06-04 21:40 ` Kent Overstreet
2023-06-05 4:05 ` Song Liu
2023-06-05 9:20 ` Mike Rapoport
2023-06-05 10:09 ` Mark Rutland
2023-06-06 10:16 ` Mike Rapoport
2023-06-06 18:21 ` Song Liu
2023-06-08 18:41 ` Mike Rapoport
2023-06-09 17:02 ` Song Liu
2023-06-12 21:34 ` Mike Rapoport
2023-06-13 18:56 ` Kent Overstreet
2023-06-13 21:09 ` Mike Rapoport
2023-07-20 8:53 ` Mike Rapoport
2023-06-05 21:13 ` Kent Overstreet [this message]
2023-06-02 0:36 ` Song Liu
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