[8u] RFR: 8144483: One long Safepoint pause directly after each GC log rotation

[cheleswer sahu]

Hi,

Please review the code changes for 
"https://bugs.openjdk.java.net/browse/JDK-8144483".

webrev link: http://cr.openjdk.java.net/~kevinw/8144483/webrev.00/
JBS link: https://bugs.openjdk.java.net/browse/JDK-8144483

Bug brief:
A long pause is observed after each gc log rotation in Solaris.

Problem Identified:
In each GC log rotation "print_memory_info()" is getting called through 
dump_loggc_header().
"print_memory_info()" of solaris version calls check_addr0(st);

File: 
http://hg.openjdk.java.net/jdk8u/jdk8u/hotspot/file/80959a760b85/src/os/solaris/vm/os_solaris.cpp

void os::print_memory_info(outputStream* st) {
   st->print("Memory:");

   st->print(" %dk page", os::vm_page_size()>>10);

   st->print(", physical " UINT64_FORMAT "k", os::physical_memory()>>10);

   st->print("(" UINT64_FORMAT "k free)", os::available_memory() >> 10);

   st->cr();
  (void) check_addr0(st);
}

Now check_addr0(st) function do a lot of read call to read the data from 
/proc/self/map.
and check if virtual address is mapped to 0x0. These read calls take lot 
of time which results in GC rotation pause.
Here calling check_addr0() seems unnecessary for every log rotation. It 
will be more logical if this function gets called only
when an error is reported.

Solution proposed:
Before GC log rotation print_memory_info() is ever getting called from 
Vm_error.cpp during error reporting. And in case of error reporting
checking for address mapping to 0x0 looks fine. So the proposed solution 
is to do an extra check inside print_memory_info().

-  (void) check_addr0(st);
+  if (VMError::fatal_error_in_progress()){
+     (void) check_addr0(st);
+  }
  }

  This check doesn't fit well inside printing function, but at this 
point I don't see the need to create a new os:: method and change all 
the OS classes just for that check.

Regards,
Cheleswer