linux-kernel - Re: [PATCH v3 18/50] tools lib api: Add io_dir an allocation free readdir alternative

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Date:   Wed, 25 Oct 2023 11:43:21 -0700
From:   Namhyung Kim <namhyung@...nel.org>
To:     Ian Rogers <irogers@...gle.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Nick Terrell <terrelln@...com>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>, Leo Yan <leo.yan@...aro.org>,
        Song Liu <song@...nel.org>,
        Sandipan Das <sandipan.das@....com>,
        James Clark <james.clark@....com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Miguel Ojeda <ojeda@...nel.org>,
        Liam Howlett <liam.howlett@...cle.com>,
        Yang Jihong <yangjihong1@...wei.com>,
        Athira Rajeev <atrajeev@...ux.vnet.ibm.com>,
        Kajol Jain <kjain@...ux.ibm.com>,
        K Prateek Nayak <kprateek.nayak@....com>,
        Sean Christopherson <seanjc@...gle.com>,
        Yanteng Si <siyanteng@...ngson.cn>,
        Ravi Bangoria <ravi.bangoria@....com>,
        German Gomez <german.gomez@....com>,
        Changbin Du <changbin.du@...wei.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        liuwenyu <liuwenyu7@...wei.com>, linux-kernel@...r.kernel.org,
        linux-perf-users@...r.kernel.org
Subject: Re: [PATCH v3 18/50] tools lib api: Add io_dir an allocation free
 readdir alternative

On Tue, Oct 24, 2023 at 3:24 PM Ian Rogers <irogers@...gle.com> wrote:
>
> glibc's opendir allocates a minimum of 32kb, when called recursively
> for a directory tree the memory consumption can add up - nearly 300kb
> during perf start-up when processing modules. Add a stack allocated
> variant of readdir sized a little more than 1kb.
>
> Signed-off-by: Ian Rogers <irogers@...gle.com>
> ---
>  tools/lib/api/Makefile |  2 +-
>  tools/lib/api/io_dir.h | 72 ++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 73 insertions(+), 1 deletion(-)
>  create mode 100644 tools/lib/api/io_dir.h
>
> diff --git a/tools/lib/api/Makefile b/tools/lib/api/Makefile
> index 044860ac1ed1..186aa407de8c 100644
> --- a/tools/lib/api/Makefile
> +++ b/tools/lib/api/Makefile
> @@ -99,7 +99,7 @@ install_lib: $(LIBFILE)
>                 $(call do_install_mkdir,$(libdir_SQ)); \
>                 cp -fpR $(LIBFILE) $(DESTDIR)$(libdir_SQ)
>
> -HDRS := cpu.h debug.h io.h
> +HDRS := cpu.h debug.h io.h io_dir.h
>  FD_HDRS := fd/array.h
>  FS_HDRS := fs/fs.h fs/tracing_path.h
>  INSTALL_HDRS_PFX := $(DESTDIR)$(prefix)/include/api
> diff --git a/tools/lib/api/io_dir.h b/tools/lib/api/io_dir.h
> new file mode 100644
> index 000000000000..8a70c0718df5
> --- /dev/null
> +++ b/tools/lib/api/io_dir.h
> @@ -0,0 +1,72 @@
> +/* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */
> +/*
> + * Lightweight directory reading library.
> + */
> +#ifndef __API_IO_DIR__
> +#define __API_IO_DIR__
> +
> +#include <dirent.h>
> +#include <fcntl.h>
> +#include <stdlib.h>
> +#include <unistd.h>
> +#include <sys/stat.h>
> +
> +struct io_dirent64 {
> +       ino64_t        d_ino;    /* 64-bit inode number */
> +       off64_t        d_off;    /* 64-bit offset to next structure */
> +       unsigned short d_reclen; /* Size of this dirent */
> +       unsigned char  d_type;   /* File type */
> +       char           d_name[NAME_MAX + 1]; /* Filename (null-terminated) */
> +};
> +
> +struct io_dir {
> +       int dirfd;
> +       ssize_t available_bytes;
> +       struct io_dirent64 *next;
> +       struct io_dirent64 buff[4];
> +};
> +
> +static inline void io_dir__init(struct io_dir *iod, int dirfd)
> +{
> +       iod->dirfd = dirfd;
> +       iod->available_bytes = 0;
> +}
> +
> +static inline void io_dir__rewinddir(struct io_dir *iod)
> +{
> +       lseek(iod->dirfd, 0, SEEK_SET);
> +       iod->available_bytes = 0;
> +}
> +
> +static inline struct io_dirent64 *io_dir__readdir(struct io_dir *iod)
> +{
> +       struct io_dirent64 *entry;
> +
> +       if (iod->available_bytes <= 0) {
> +               ssize_t rc = getdents64(iod->dirfd, iod->buff, sizeof(iod->buff));
> +
> +               if (rc <= 0)
> +                       return NULL;
> +               iod->available_bytes = rc;
> +               iod->next = iod->buff;
> +       }
> +       entry = iod->next;
> +       iod->next = (struct io_dirent64 *)((char *)entry + entry->d_reclen);

Any chance of unaligned access?


> +       iod->available_bytes -= entry->d_reclen;
> +       return entry;
> +}
> +
> +static inline bool io_dir__is_dir(const struct io_dir *iod, const struct io_dirent64 *dent)
> +{
> +       if (dent->d_type == DT_UNKNOWN) {
> +               struct stat st;
> +
> +               if (fstatat(iod->dirfd, dent->d_name, &st, /*flags=*/0))
> +                       return false;
> +
> +               return S_ISDIR(st.st_mode);

You may want to save the type if it's a DIR.

Thanks,
Namhyung


> +       }
> +       return dent->d_type == DT_DIR;
> +}
> +
> +#endif
> --
> 2.42.0.758.gaed0368e0e-goog
>