Re: [PATCH v2 7/7] perf expr: Migrate expr ids table to a hashmap

From: Ian Rogers <irogers@google.com>
To: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
	Yonghong Song <yhs@fb.com>, Andrii Nakryiko <andriin@fb.com>,
	John Fastabend <john.fastabend@gmail.com>,
	KP Singh <kpsingh@chromium.org>, Kajol Jain <kjain@linux.ibm.com>,
	Andi Kleen <ak@linux.intel.com>,
	John Garry <john.garry@huawei.com>,
	Jin Yao <yao.jin@linux.intel.com>,
	Kan Liang <kan.liang@linux.intel.com>,
	Cong Wang <xiyou.wangcong@gmail.com>,
	Kim Phillips <kim.phillips@amd.com>,
	Adrian Hunter <adrian.hunter@intel.com>,
	Leo Yan <leo.yan@linaro.org>,
	open list <linux-kernel@vger.kernel.org>,
	Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
	Stephane Eranian <eranian@google.com>
Subject: Re: [PATCH v2 7/7] perf expr: Migrate expr ids table to a hashmap
Date: Fri, 15 May 2020 15:03:16 -0700	[thread overview]
Message-ID: <CAP-5=fV83V_DxaR8M4LXgS-s-+gW18Q3UmfjrpAkz4u2K4B7MA@mail.gmail.com> (raw)
In-Reply-To: <CAEf4BzZOB0L0iie0CAduNOnE4TXbfKeo-g97kwfMPZ5Mg7uRwg@mail.gmail.com>

On Fri, May 15, 2020 at 12:39 PM Andrii Nakryiko
<andrii.nakryiko@gmail.com> wrote:
>
> On Fri, May 15, 2020 at 9:51 AM Ian Rogers <irogers@google.com> wrote:
> >
> > Use a hashmap between a char* string and a double* value. While bpf's
> > hashmap entries are size_t in size, we can't guarantee sizeof(size_t) >=
> > sizeof(double). Avoid a memory allocation when gathering ids by making 0.0
> > a special value encoded as NULL.
> >
> > Original map suggestion by Andi Kleen:
> > https://lore.kernel.org/lkml/20200224210308.GQ160988@tassilo.jf.intel.com/
> > and seconded by Jiri Olsa:
> > https://lore.kernel.org/lkml/20200423112915.GH1136647@krava/
> >
> > Signed-off-by: Ian Rogers <irogers@google.com>
> > ---
> >  tools/perf/tests/expr.c       |  40 ++++++-----
> >  tools/perf/tests/pmu-events.c |  25 +++----
> >  tools/perf/util/expr.c        | 129 +++++++++++++++++++---------------
> >  tools/perf/util/expr.h        |  26 +++----
> >  tools/perf/util/expr.y        |  22 +-----
> >  tools/perf/util/metricgroup.c |  87 +++++++++++------------
> >  tools/perf/util/stat-shadow.c |  49 ++++++++-----
> >  7 files changed, 197 insertions(+), 181 deletions(-)
> >
> > diff --git a/tools/perf/tests/expr.c b/tools/perf/tests/expr.c
> > index 3f742612776a..5e606fd5a2c6 100644
> > --- a/tools/perf/tests/expr.c
> > +++ b/tools/perf/tests/expr.c
> > @@ -19,11 +19,9 @@ static int test(struct expr_parse_ctx *ctx, const char *e, double val2)
> >  int test__expr(struct test *t __maybe_unused, int subtest __maybe_unused)
> >  {
> >         const char *p;
> > -       const char **other;
> > -       double val;
> > -       int i, ret;
> > +       double val, *val_ptr;
> > +       int ret;
> >         struct expr_parse_ctx ctx;
> > -       int num_other;
> >
> >         expr__ctx_init(&ctx);
> >         expr__add_id(&ctx, "FOO", 1);
> > @@ -52,25 +50,29 @@ int test__expr(struct test *t __maybe_unused, int subtest __maybe_unused)
> >         ret = expr__parse(&val, &ctx, p, 1);
> >         TEST_ASSERT_VAL("missing operand", ret == -1);
> >
> > +       hashmap__clear(&ctx.ids);
>
> hashmap__clear() will free up memory allocated for hashmap itself and
> hash entries, but not keys/values. Unless it's happening somewhere
> else, you'll need to do something similar to expr__ctx_clear() below?

In this case the const char* keys come from the literals added on
lines 27 and 28 and so didn't need free-ing - which is what
expr__ctx_clear() does. I've made these literals strdups and switched
to expr__ctx_clear() as you suggest, as this is more reflective of the
real use.

> Same below for another "lone" hashmap_clear() call.

This was a memory leak, thanks!
Ian

> >         TEST_ASSERT_VAL("find other",
> > -                       expr__find_other("FOO + BAR + BAZ + BOZO", "FOO", &other, &num_other, 1) == 0);
>
> [...]