From: Song Liu <songliubraving@fb.com>
To: Andrii Nakryiko <andriin@fb.com>
Cc: bpf <bpf@vger.kernel.org>,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
Alexei Starovoitov <ast@fb.com>,
"daniel@iogearbox.net" <daniel@iogearbox.net>,
"andrii.nakryiko@gmail.com" <andrii.nakryiko@gmail.com>,
Kernel Team <Kernel-team@fb.com>, Rik van Riel <riel@surriel.com>,
Johannes Weiner <hannes@cmpxchg.org>
Subject: Re: [PATCH bpf-next 1/3] bpf: add mmap() support for BPF_MAP_TYPE_ARRAY
Date: Fri, 8 Nov 2019 06:39:44 +0000 [thread overview]
Message-ID: <94BD3FAC-CA98-4448-B467-3FC7307174F9@fb.com> (raw)
In-Reply-To: <20191108042041.1549144-2-andriin@fb.com>
> On Nov 7, 2019, at 8:20 PM, Andrii Nakryiko <andriin@fb.com> wrote:
>
> Add ability to memory-map contents of BPF array map. This is extremely useful
> for working with BPF global data from userspace programs. It allows to avoid
> typical bpf_map_{lookup,update}_elem operations, improving both performance
> and usability.
>
> There had to be special considerations for map freezing, to avoid having
> writable memory view into a frozen map. To solve this issue, map freezing and
> mmap-ing is happening under mutex now:
> - if map is already frozen, no writable mapping is allowed;
> - if map has writable memory mappings active (accounted in map->writecnt),
> map freezing will keep failing with -EBUSY;
> - once number of writable memory mappings drops to zero, map freezing can be
> performed again.
>
> Only non-per-CPU arrays are supported right now. Maps with spinlocks can't be
> memory mapped either.
>
> Cc: Rik van Riel <riel@surriel.com>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Song Liu <songliubraving@fb.com>
With one nit below.
[...]
> - if (percpu)
> + data_size = 0;
> + if (percpu) {
> array_size += (u64) max_entries * sizeof(void *);
> - else
> - array_size += (u64) max_entries * elem_size;
> + } else {
> + if (attr->map_flags & BPF_F_MMAPABLE) {
> + data_size = (u64) max_entries * elem_size;
> + data_size = round_up(data_size, PAGE_SIZE);
> + } else {
> + array_size += (u64) max_entries * elem_size;
> + }
> + }
>
> /* make sure there is no u32 overflow later in round_up() */
> - cost = array_size;
> + cost = array_size + data_size;
This is a little confusing. Maybe we can do
data_size = (u64) max_entries * (per_cpu ? sizeof(void *) : elem_size;
if (attr->map_flags & BPF_F_MMAPABLE)
data_size = round_up(data_size, PAGE_SIZE);
cost = array_size + data_size;
So we use data_size in all cases.
Maybe also rename array_size.
> if (percpu)
> cost += (u64)attr->max_entries * elem_size * num_possible_cpus();
And maybe we can also include this in data_size.
[...]
next prev parent reply other threads:[~2019-11-08 6:40 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-08 4:20 [PATCH bpf-next 0/3] Add support for memory-mapping BPF array maps Andrii Nakryiko
2019-11-08 4:20 ` [PATCH bpf-next 1/3] bpf: add mmap() support for BPF_MAP_TYPE_ARRAY Andrii Nakryiko
2019-11-08 6:39 ` Song Liu [this message]
2019-11-08 19:34 ` Andrii Nakryiko
2019-11-11 16:39 ` Song Liu
2019-11-08 4:20 ` [PATCH bpf-next 2/3] libbpf: make global data internal arrays mmap()-able, if possible Andrii Nakryiko
2019-11-08 6:44 ` Song Liu
2019-11-08 19:34 ` Andrii Nakryiko
2019-11-08 4:20 ` [PATCH bpf-next 3/3] selftests/bpf: add BPF_TYPE_MAP_ARRAY mmap() tests Andrii Nakryiko
2019-11-08 6:49 ` Song Liu
2019-11-08 22:08 ` [PATCH bpf-next 0/3] Add support for memory-mapping BPF array maps Stanislav Fomichev
2019-11-08 23:19 ` Andrii Nakryiko
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=94BD3FAC-CA98-4448-B467-3FC7307174F9@fb.com \
--to=songliubraving@fb.com \
--cc=Kernel-team@fb.com \
--cc=andrii.nakryiko@gmail.com \
--cc=andriin@fb.com \
--cc=ast@fb.com \
--cc=bpf@vger.kernel.org \
--cc=daniel@iogearbox.net \
--cc=hannes@cmpxchg.org \
--cc=netdev@vger.kernel.org \
--cc=riel@surriel.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).