Re: [PATCH v4 06/53] tools api fs: Switch filename__read_str to use io.h

[Namhyung Kim]

On Thu, Nov 2, 2023 at 10:58 AM Ian Rogers <irogers@xxxxxxxxxx> 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@xxxxxxxxxx>
> ---

[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
>