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    SubjectRe: [PATCH bpf-next v2 27/35] bpf: eliminate rlimit-based memory accounting infra for bpf maps
    On Mon, Jul 27, 2020 at 11:06:42PM -0700, Song Liu wrote:
    > On Mon, Jul 27, 2020 at 10:58 PM Andrii Nakryiko
    > <andrii.nakryiko@gmail.com> wrote:
    > >
    > > On Mon, Jul 27, 2020 at 10:47 PM Song Liu <song@kernel.org> wrote:
    > > >
    > > > On Mon, Jul 27, 2020 at 12:26 PM Roman Gushchin <guro@fb.com> wrote:
    > > > >
    > > > > Remove rlimit-based accounting infrastructure code, which is not used
    > > > > anymore.
    > > > >
    > > > > Signed-off-by: Roman Gushchin <guro@fb.com>
    > > > [...]
    > > > >
    > > > > static void bpf_map_put_uref(struct bpf_map *map)
    > > > > @@ -541,7 +484,7 @@ static void bpf_map_show_fdinfo(struct seq_file *m, struct file *filp)
    > > > > "value_size:\t%u\n"
    > > > > "max_entries:\t%u\n"
    > > > > "map_flags:\t%#x\n"
    > > > > - "memlock:\t%llu\n"
    > > > > + "memlock:\t%llu\n" /* deprecated */
    > > >
    > > > I am not sure whether we can deprecate this one.. How difficult is it
    > > > to keep this statistics?
    > > >
    > >
    > > It's factually correct now, that BPF map doesn't use any memlock memory, no?

    Right.

    >
    > I am not sure whether memlock really means memlock for all users... I bet there
    > are users who use memlock to check total memory used by the map.

    But this is just the part of struct bpf_map, so I agree with Andrii,
    it's a safe check.

    >
    > >
    > > This is actually one way to detect whether RLIMIT_MEMLOCK is necessary
    > > or not: create a small map, check if it's fdinfo has memlock: 0 or not
    > > :)
    >
    > If we do show memlock=0, this is a good check...

    The only question I have if it's worth checking at all? Bumping the rlimit
    is a way cheaper operation than creating a temporarily map and checking its
    properties.

    So is there any win in comparison to just leaving the userspace code* as it is
    for now?

    * except runqslower and samples

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