From: Jakub Kicinski <jakub.kicinski@netronome.com>
To: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: Andrii Nakryiko <andriin@fb.com>, bpf <bpf@vger.kernel.org>,
Networking <netdev@vger.kernel.org>,
Alexei Starovoitov <ast@fb.com>,
Daniel Borkmann <daniel@iogearbox.net>,
Kernel Team <kernel-team@fb.com>, Rik van Riel <riel@surriel.com>,
Johannes Weiner <hannes@cmpxchg.org>
Subject: Re: [PATCH v2 bpf-next 1/3] bpf: add mmap() support for BPF_MAP_TYPE_ARRAY
Date: Tue, 12 Nov 2019 11:17:50 -0800 [thread overview]
Message-ID: <20191112111750.2168b131@cakuba> (raw)
In-Reply-To: <CAEf4Bzay-sCd5+5Y1+toJuEd6vNh+R7pkosYA7V7wDqTdoDxdw@mail.gmail.com>
On Mon, 11 Nov 2019 18:06:42 -0800, Andrii Nakryiko wrote:
> So let's say if sizeof(struct bpf_array) is 300, then I'd have to either:
>
> - somehow make sure that I allocate 4k (for data) + 300 (for struct
> bpf_array) in such a way that those 4k of data are 4k-aligned. Is
> there any way to do that?
> - assuming there isn't, then another way would be to allocate entire
> 4k page for struct bpf_array itself, but put it at the end of that
> page, so that 4k of data is 4k-aligned. While wasteful, the bigger
> problem is that pointer to bpf_array is not a pointer to allocated
> memory anymore, so we'd need to remember that and adjust address
> before calling vfree().
>
> Were you suggesting #2 as a solution? Or am I missing some other way to do this?
I am suggesting #2, that's the way to do it in the kernel.
You could make the assumption that if you're allocating memory aligned
to PAGE_SIZE, the address for vfree() is:
addr = map;
if (map->flags & MMAPABLE)
addr = round_down(addr, PAGE_SIZE);
vfree(addr);
Just make a note of the fact that we depend on vmalloc()s alignment in
bpf_map_area_alloc().
next prev parent reply other threads:[~2019-11-12 19:18 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-09 8:06 [PATCH v2 bpf-next 0/3] Add support for memory-mapping BPF array maps Andrii Nakryiko
2019-11-09 8:06 ` [PATCH v2 bpf-next 1/3] bpf: add mmap() support for BPF_MAP_TYPE_ARRAY Andrii Nakryiko
2019-11-11 16:40 ` Song Liu
2019-11-11 18:37 ` Jakub Kicinski
2019-11-12 2:06 ` Andrii Nakryiko
2019-11-12 19:17 ` Jakub Kicinski [this message]
2019-11-12 22:03 ` Andrii Nakryiko
2019-11-12 22:38 ` Jakub Kicinski
2019-11-13 3:19 ` Andrii Nakryiko
2019-11-11 18:39 ` Jakub Kicinski
2019-11-12 2:01 ` Andrii Nakryiko
2019-11-09 8:06 ` [PATCH v2 bpf-next 2/3] libbpf: make global data internal arrays mmap()-able, if possible Andrii Nakryiko
2019-11-11 18:40 ` Jakub Kicinski
2019-11-12 2:11 ` Andrii Nakryiko
2019-11-09 8:06 ` [PATCH v2 bpf-next 3/3] selftests/bpf: add BPF_TYPE_MAP_ARRAY mmap() tests Andrii Nakryiko
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