Re: [Tarantool-patches] [PATCH luajit v2 6/7] misc: add Lua API for memory profiler

[Igor Munkin <imun@tarantool.org>]

Sergey,

Thanks for the patch! Please consider the comments below.

On 25.12.20, Sergey Kaplun wrote:
> This patch introduces Lua API for LuaJIT memory profiler implemented in
> the scope of the previous patch.
> 
> Profiler returns some true value if started/stopped successfully,

There is no "some" true value there is a sole one. Please fix it in both
the patch and the RFC.

> returns nil on failure (plus an error message as a second result and a
> system-dependent error code as a third result).
> If LuaJIT build without memory profiler both return `false`.
> 
> <lj_errmsg.h> have adjusted with two new errors
> PROF_ISRUNNING/PROF_NOTRUNNING returned in case when profiler has
> started/stopped already correspondingly.
> 
> Part of tarantool/tarantool#5442
> ---
> 
> Changes in v2:
>   - Added pushing of errno for ERR_PROF* and ERRMEM
>   - Added forgotten assert.
> 
>  src/Makefile.dep |   5 +-
>  src/lib_misc.c   | 167 +++++++++++++++++++++++++++++++++++++++++++++++
>  src/lj_errmsg.h  |   6 ++
>  3 files changed, 176 insertions(+), 2 deletions(-)
> 

<snipped>

> diff --git a/src/lib_misc.c b/src/lib_misc.c
> index 6f7b9a9..36fe29f 100644
> --- a/src/lib_misc.c
> +++ b/src/lib_misc.c

<snipped>

> @@ -67,8 +75,167 @@ LJLIB_CF(misc_getmetrics)

<snipped>

> +static LJ_AINLINE void memprof_ctx_free(struct memprof_ctx *ctx, uint8_t *buf)
> +{
> +  lj_mem_free(ctx->g, buf, STREAM_BUFFER_SIZE);

Side note: This is odd that you free the buffer here, but the buffer
itself is not a part of the memprof context. Let's return to this later.

> +  lj_mem_free(ctx->g, ctx, sizeof(*ctx));
> +}
> +
> +/* Default buffer writer function. Just call fwrite to corresponding FILE. */
> +static size_t buffer_writer_default(const void **buf_addr, size_t len,
> +				    void *opt)
> +{

<snipped>

> +    if (LJ_UNLIKELY(written == 0)) {
> +      /* Re-tries write in case of EINTR. */
> +      if (errno == EINTR) {

Minor: It's better to use early return here. Feel free to ignore.

> +	errno = 0;
> +	continue;
> +      }
> +      break;

If other error occurs, you need to pass the NULL to buf_addr, right?
Otherwise, there is no guarantee everything is written to the file and
profiling proceeds.

> +    }

<snipped>

> +
> +/* Default on stop callback. Just close corresponding stream. */

Typo: s/close corresponding/close the corresponding/.

> +static int on_stop_cb_default(void *opt, uint8_t *buf)

<snipped>

> +/* local started, err, errno = misc.memprof.start(fname) */
> +LJLIB_CF(misc_memprof_start)
> +{

<snipped>

> +  fname = strdata(lj_lib_checkstr(L, 1));

Minor: You can make this assignment alongside with the declaration.

> +
> +  ctx = lj_mem_new(L, sizeof(*ctx));
> +  if (ctx == NULL)

This is a dead code: <lj_mem_new> raises a LUA_ERRMEM.

> +    goto errmem;
> +

<snipped>

> +  if (NULL == opt.buf) {

This is a dead code: <lj_mem_new> raises a LUA_ERRMEM.

> +    lj_mem_free(G(L), ctx, sizeof(*ctx));
> +    goto errmem;
> +  }

<snipped>

> +  memprof_status = lj_memprof_start(L, &opt);
> +  started = memprof_status == PROFILE_SUCCESS;

Trust me, you don't need this variable.
*/me making Jedi mind tricks here*

> +
> +  if (LJ_UNLIKELY(!started)) {
> +    fclose(ctx->stream);
> +    remove(fname);

Minor: I doubt we need to remove a file even if LuaJIT failed to start
profiling. Leave the comment if this makes sense. Feel free to ignore.

> +    memprof_ctx_free(ctx, opt.buf);
> +    switch (memprof_status) {

<snipped>

> +    }
> +  }
> +  lua_pushboolean(L, started);

Please, s/started/1/ since there is no another value here.

> +
> +  return 1;

<snipped>

> +}
> +
> +/* local stopped, err, errno = misc.memprof.stop() */
> +LJLIB_CF(misc_memprof_stop)
> +{
> +  int status = lj_memprof_stop();
> +  int stopped_successfully = status == PROFILE_SUCCESS;

Trust me, you don't need this variable.
*/me making Jedi mind tricks here*

> +  if (!stopped_successfully) {

<snipped>

> +  lua_pushboolean(L, stopped_successfully);

Please, s/stopped_succesfully/1/ since there is no another value here.

> +  return 1;
> +}
> +

<snipped>

> diff --git a/src/lj_errmsg.h b/src/lj_errmsg.h
> index de7b867..6816da2 100644
> --- a/src/lj_errmsg.h
> +++ b/src/lj_errmsg.h
> @@ -185,6 +185,12 @@ ERRDEF(FFI_NYIPACKBIT,	"NYI: packed bit fields")

<snipped>

> +#if LJ_HASPROFILE || LJ_HASMEMPROF

Why did you also initialize them for <jit.p> profiler?

> +/* Profiler errors. */

<snipped>

> -- 
> 2.28.0
> 

-- 
Best regards,
IM