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

[Sergey Kaplun <skaplun@tarantool.org>]

Hi!

Thanks for your feedback!

On 30.01.20, Leonid Vasiliev wrote:
> 
> Hi.
> 
> On 1/29/20 4:36 PM, Sergey Ostanevich wrote:
> > 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 :)
> 
> Hmm, it's sounds like:"Client must known about implementation of library 
> function". But implementation can be changed with the contract save.
> 

To be honest, I do not see any dependencies on internal API in this,
since the module determines SMALL_STATIC_SIZE and provides

    extern __thread char static_storage_buffer[SMALL_STATIC_SIZE];

- all of this is part of API, isn't it?

Proposal: we can use sizeof(static_storage_buffer) to avoid usage
of "magic" SMALL_STATIC_SIZE.

> > 
> > 
> > 
> >>
> >> 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) {
> >>>