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From:   Namhyung Kim <namhyung@kernel.org>
Date:   Sun, 5 Nov 2023 19:53:00 -0800
Message-ID: <CAM9d7chgQBGMmyDyi98OUzyJHWaNUfw34VD=pStkX_n-t5Vpkg@mail.gmail.com>
Subject: Re: [PATCH v4 06/53] tools api fs: Switch filename__read_str to use io.h
To:     Ian Rogers <irogers@google.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>,
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        Kan Liang <kan.liang@linux.intel.com>,
        Andi Kleen <ak@linux.intel.com>,
        Kajol Jain <kjain@linux.ibm.com>,
        Athira Rajeev <atrajeev@linux.vnet.ibm.com>,
        Huacai Chen <chenhuacai@kernel.org>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Vincent Whitchurch <vincent.whitchurch@axis.com>,
        "Steinar H. Gunderson" <sesse@google.com>,
        Liam Howlett <liam.howlett@oracle.com>,
        Miguel Ojeda <ojeda@kernel.org>,
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        James Clark <james.clark@arm.com>,
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        Sean Christopherson <seanjc@google.com>,
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        Changbin Du <changbin.du@huawei.com>,
        Paolo Bonzini <pbonzini@redhat.com>, Li Dong <lidong@vivo.com>,
        Sandipan Das <sandipan.das@amd.com>,
        liuwenyu <liuwenyu7@huawei.com>, linux-kernel@vger.kernel.org,
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On Thu, Nov 2, 2023 at 10:58 AM Ian Rogers <irogers@google.com> wrote:
>
> filename__read_str has its own string reading code that allocates
> memory before reading into it. The memory allocated is sized at BUFSIZ
> that is 8kb. Most strings are short and so most of this 8kb is
> wasted.
>
> Refactor io__getline so that the newline character can be configurable
> and ignored in the case of filename__read_str.
>
> Code like build_caches_for_cpu in perf's header.c will read many
> strings and hold them in a data structure, in this case multiple
> strings per cache level per CPU. Using io.h's io__getline avoids the
> wasted memory as strings are temporarily read into a buffer on the
> stack before being copied to a buffer that grows 128 bytes at a time
> and is never sized larger than the string.
>
> For a 16 hyperthread system the memory consumption of "perf record
> true" is reduced by 180kb, primarily through saving memory when
> reading the cache information.
>
> Signed-off-by: Ian Rogers <irogers@google.com>
> ---

[SNIP]
> diff --git a/tools/lib/api/io.h b/tools/lib/api/io.h
> index a77b74c5fb65..50d33e14fb56 100644
> --- a/tools/lib/api/io.h
> +++ b/tools/lib/api/io.h
> @@ -141,7 +141,7 @@ static inline int io__get_dec(struct io *io, __u64 *dec)
>  }
>
>  /* Read up to and including the first newline following the pattern of getline. */

You may want to update the comment as well.

> -static inline ssize_t io__getline(struct io *io, char **line_out, size_t *line_len_out)
> +static inline ssize_t io__getline_nl(struct io *io, char **line_out, size_t *line_len_out, int nl)

How about io__getdelim() similar to POSIX?

Thanks,
Namhyung


>  {
>         char buf[128];
>         int buf_pos = 0;
> @@ -151,7 +151,7 @@ static inline ssize_t io__getline(struct io *io, char **line_out, size_t *line_l
>
>         /* TODO: reuse previously allocated memory. */
>         free(*line_out);
> -       while (ch != '\n') {
> +       while (ch != nl) {
>                 ch = io__get_char(io);
>
>                 if (ch < 0)
> @@ -184,4 +184,9 @@ static inline ssize_t io__getline(struct io *io, char **line_out, size_t *line_l
>         return -ENOMEM;
>  }
>
> +static inline ssize_t io__getline(struct io *io, char **line_out, size_t *line_len_out)
> +{
> +       return io__getline_nl(io, line_out, line_len_out, /*nl=*/'\n');
> +}
> +
>  #endif /* __API_IO__ */
> --
> 2.42.0.869.gea05f2083d-goog
>