Re: [Tarantool-patches] [PATCH v2] refactoring: drop excess 16Kb bss buffer

[Sergey Ostanevich <sergos@tarantool.org>]

Hi!

Thanks for the patch!

LGTM after updates below.

Regards,
Sergos


On 23 Jan 23:04, Vladislav Shpilevoy wrote:
> Hi! Thanks for the patch!
> 
> I agree with everything what Leonid said.

I will object both assertion and NULL handling. Just have a look:

> > +   char *backtrace_buf = (char *)static_alloc(SMALL_STATIC_SIZE);

And in static_reserve(size_t size) called from static_alloc():

                if (size > SMALL_STATIC_SIZE)
                                        return NULL;

is the only place NULL can be returned. No need to test if
SMALL_STATIC_SIZE > SMALL_STATIC_SIZE, just ask me :)



> 
> On 23/01/2020 09:44, Sergey Kaplun wrote:
> > We already have 12Kb thread-safe static buffer
> > in `lib/small/small/static.h`, that can be used instead of 16Kb
> > bss buffer in `src/lib/core/backtrace.cc` for backtrace payload.
> > Closes #4650
> > ---
> > 
> > branch: https://github.com/tarantool/tarantool/tree/skaplun/drop-bss-buff
> > issue: https://github.com/tarantool/tarantool/issues/4650
> > 
> >  src/lib/core/backtrace.cc | 8 +++++---
> >  1 file changed, 5 insertions(+), 3 deletions(-)
> > 
> > diff --git a/src/lib/core/backtrace.cc b/src/lib/core/backtrace.cc
> > index 77f77b05c..c70576b53 100644
> > --- a/src/lib/core/backtrace.cc
> > +++ b/src/lib/core/backtrace.cc
> > @@ -33,6 +33,7 @@
> >  
> >  #include <stdlib.h>
> >  #include <stdio.h>
> > +#include <assert.h>
> >  
> >  #include <cxxabi.h>
> >  
> > @@ -47,6 +48,7 @@
> >  #include <libunwind.h>
> >  
> >  #include "small/region.h"
> > +#include "small/static.h"
> >  /*
> >   * We use a global static buffer because it is too late to do any
> >   * allocation when we are printing backtrace and fiber stack is

Just change "global static buffer" for the "static buffer interface".

> > @@ -55,8 +57,6 @@
> >  
> >  #define BACKTRACE_NAME_MAX 200
> >  
> > -static char backtrace_buf[4096 * 4];
> > -
> >  static __thread struct region cache_region;
> >  static __thread struct mh_i64ptr_t *proc_cache = NULL;
> >  
> > @@ -140,8 +140,10 @@ backtrace()
> >  	unw_getcontext(&unw_context);
> >  	unw_cursor_t unw_cur;
> >  	unw_init_local(&unw_cur, &unw_context);
> > +	char *backtrace_buf = (char *)static_alloc(SMALL_STATIC_SIZE);
> > +	assert(backtrace_buf);
> >  	char *p = backtrace_buf;
> > -	char *end = p + sizeof(backtrace_buf) - 1;
> > +	char *end = p + SMALL_STATIC_SIZE - 1;
> >  	int unw_status;
> >  	*p = '\0';
> >  	while ((unw_status = unw_step(&unw_cur)) > 0) {
> >