From: Mike Rapoport <rppt@kernel.org>
To: Song Liu <song@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>,
Andrii Nakryiko <andrii@kernel.org>,
Andy Lutomirski <luto@kernel.org>, Borislav Petkov <bp@alien8.de>,
Daniel Borkmann <daniel@iogearbox.net>,
Dave Hansen <dave.hansen@linux.intel.com>,
Eduard Zingerman <eddyz87@gmail.com>,
Ingo Molnar <mingo@redhat.com>,
Kumar Kartikeya Dwivedi <memxor@gmail.com>,
Peter Zijlstra <peterz@infradead.org>,
Thomas Gleixner <tglx@kernel.org>,
Emil Tsalapatis <emil@etsalapatis.com>,
Jiri Olsa <jolsa@kernel.org>,
John Fastabend <john.fastabend@gmail.com>,
Martin KaFai Lau <martin.lau@linux.dev>,
"H. Peter Anvin" <hpa@zytor.com>,
Yonghong Song <yonghong.song@linux.dev>,
bpf@vger.kernel.org, linux-kernel@vger.kernel.org,
x86@kernel.org
Subject: Re: [PATCH bpf-next v3 0/5] bpf, x86: enable EXECMEM_ROX_CACHE for BPF allocations
Date: Wed, 22 Jul 2026 11:05:47 +0300 [thread overview]
Message-ID: <amB52yECfXNgbeY4@kernel.org> (raw)
In-Reply-To: <CAPhsuW6+6zcSRGUAtp=3e4a8at3yuRP8Xijb-4LBHtQ8Li6wrQ@mail.gmail.com>
On Tue, Jul 21, 2026 at 10:59:06AM -0700, Song Liu wrote:
> On Sun, Jul 19, 2026 at 2:23 AM Mike Rapoport <rppt@kernel.org> wrote:
> > > >
> > > > Since commit c82be0be9576 ("mm: vmalloc: don't account for number of nodes
> > > > for HUGE_VMAP allocations") vmalloc_huge() is fine with PMD_SIZE regardless
> > > > of number of nodes.
> > >
> > > Before execmem can handle sub page allocations, how about we
> > > send allocations that are bigger than page size directly to execmem,
> > > and let bpf_prog_pack handle sub page allocations. Then,
> > > BPF_PROG_PACK_SIZE will be PAGE_SIZE. This should be a net
> > > win for x86_64. Other archs will be the same. WDYT?
> >
> > Makes perfect sense to me for x86.
>
> Can we include this change to this patch set? This will make this
> change a meaningful step towards migrating to EXECMEM.
I'd prefer to leave this as a separate followup.
The decision whether to use EXECMEM_ROX_CACHE is made at runtime, which
means that BPF_PROG_PACK_SIZE should become a variable, that variable needs
initialization at some point during boot and that in turn requires a new
helper in execmem that will say if EXECMEM_CACHE_ROX is enabled.
> > On architectures that support large mappings in the direct map and do not
> > support EXECMEM_CACHE_ROX this will increase direct map fragmentation.
>
> Architectures that support bpf_prog_pack can benefit from
> EXECMEM_CACHE_ROX. What does it take to also enable
> EXECMEM_CACHE_ROX for them?
For EXECMEM_ROX_CACHE to help in reducing the fragmentation and TLB
pressure an architecture should support collapsing of the split mappings at
least in vmalloc/modules space.
There is an RFC for arm64 to add support for EXECMEM_ROX_CACHE there:
https://lore.kernel.org/all/20260611130144.1385343-1-abarnas@google.com
and it looks like it'll take a couple of iterations :)
I don't how much work it would be for other architectures.
> Thanks,
> Song
--
Sincerely yours,
Mike.
next prev parent reply other threads:[~2026-07-22 8:06 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-16 7:51 [PATCH bpf-next v3 0/5] bpf, x86: enable EXECMEM_ROX_CACHE for BPF allocations Mike Rapoport (Microsoft)
2026-07-16 7:51 ` [PATCH bpf-next v3 1/5] bpf: dispatcher: allocate bpf_dispatcher->rw_image with vzalloc() Mike Rapoport (Microsoft)
2026-07-16 8:52 ` bot+bpf-ci
2026-07-16 9:27 ` Mike Rapoport
2026-07-16 9:49 ` Kumar Kartikeya Dwivedi
2026-07-16 7:51 ` [PATCH bpf-next v3 2/5] bpf: drop __weak from bpf_jit_alloc_exec() and bpf_jit_free_exec() Mike Rapoport (Microsoft)
2026-07-16 7:51 ` [PATCH bpf-next v3 3/5] bpf: alloc_prog_pack(): skip ROX management for already ROX memory Mike Rapoport (Microsoft)
2026-07-16 7:51 ` [PATCH bpf-next v3 4/5] bpf, x86: make sure allocation in arch_bpf_trampoline_size() is writable Mike Rapoport (Microsoft)
2026-07-16 7:51 ` [PATCH bpf-next v3 5/5] x86/bpf: enable EXECMEM_ROX_CACHE for BPF allocations Mike Rapoport (Microsoft)
2026-07-17 0:00 ` [PATCH bpf-next v3 0/5] bpf, x86: " Song Liu
2026-07-17 6:41 ` Mike Rapoport
2026-07-17 7:27 ` Song Liu
2026-07-17 9:29 ` Mike Rapoport
2026-07-17 17:50 ` Song Liu
2026-07-19 9:23 ` Mike Rapoport
2026-07-21 17:59 ` Song Liu
2026-07-22 8:05 ` Mike Rapoport [this message]
2026-07-22 15:04 ` Song Liu
2026-07-22 15:40 ` patchwork-bot+netdevbpf
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