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From: Song Liu <song@kernel.org>
Date: Thu, 18 Apr 2024 14:01:22 -0700
Message-ID: <CAPhsuW5SL4_=ZXdHZV8o0KS+5Vf25UMvEKhRgFQLioFtf2pgoQ@mail.gmail.com>
Subject: Re: [PATCH v4 05/15] mm: introduce execmem_alloc() and execmem_free()
To: Mike Rapoport <rppt@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>, Peter Zijlstra <peterz@infradead.org>, 
	linux-kernel@vger.kernel.org, Alexandre Ghiti <alexghiti@rivosinc.com>, 
	Andrew Morton <akpm@linux-foundation.org>, Bjorn Topel <bjorn@kernel.org>, 
	Catalin Marinas <catalin.marinas@arm.com>, Christophe Leroy <christophe.leroy@csgroup.eu>, 
	"David S. Miller" <davem@davemloft.net>, Dinh Nguyen <dinguyen@kernel.org>, 
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On Thu, Apr 18, 2024 at 10:54=E2=80=AFAM Mike Rapoport <rppt@kernel.org> wr=
ote:
>
> On Thu, Apr 18, 2024 at 09:13:27AM -0700, Song Liu wrote:
> > On Thu, Apr 18, 2024 at 8:37=E2=80=AFAM Mike Rapoport <rppt@kernel.org>=
 wrote:
> > > > >
> > > > > I'm looking at execmem_types more as definition of the consumers,=
 maybe I
> > > > > should have named the enum execmem_consumer at the first place.
> > > >
> > > > I think looking at execmem_type from consumers' point of view adds
> > > > unnecessary complexity. IIUC, for most (if not all) archs, ftrace, =
kprobe,
> > > > and bpf (and maybe also module text) all have the same requirements=
.
> > > > Did I miss something?
> > >
> > > It's enough to have one architecture with different constrains for kp=
robes
> > > and bpf to warrant a type for each.
> >
> > AFAICT, some of these constraints can be changed without too much work.
>
> But why?
> I honestly don't understand what are you trying to optimize here. A few
> lines of initialization in execmem_info?

IIUC, having separate EXECMEM_BPF and EXECMEM_KPROBE makes it
harder for bpf and kprobe to share the same ROX page. In many use cases,
a 2MiB page (assuming x86_64) is enough for all BPF, kprobe, ftrace, and
module text. It is not efficient if we have to allocate separate pages for =
each
of these use cases. If this is not a problem, the current approach works.

Thanks,
Song