Update Scudo allocator documentation.

[flowerhack]

Summary

QuarantineSizeMb is deprecated, and QuarantineChunksUpToSize has been added as a new tunable option.

[cryptoad]

Thanks, it slipped my mind to update the doc. Couple of comments.

docs/ScudoHardenedAllocator.rst

145

(in Kb) in the description.

151

So here lower values will not necessarily lower the memory usage as we'll fill up to QuarantineSizeKb bytes anyway.
I'd go for "Size (in bytes) up to which chunks can be quarantined."

[flowerhack]

Made requested fixes.

[flowerhack]

Do you have commit privileges or shall I fetch someone else?

docs/ScudoHardenedAllocator.rst

 ``whole-archive`` linker flag (or equivalent), depending on your linker.
 Additional flags might also be necessary.
 
 Your linked binary should now make use of the Scudo allocation and deallocation
 functions.
 
 You may also build Scudo like this: 
 
-.. code::
+.. code:: none
 
   cd $LLVM/projects/compiler-rt/lib
   clang++ -fPIC -std=c++11 -msse4.2 -O2 -I. scudo/*.cpp \
     $(\ls sanitizer_common/*.{cc,S} | grep -v "sanitizer_termination\|sanitizer_common_nolibc") \
     -shared -o scudo-allocator.so -pthread
 
 and then use it with existing binaries as follows:
 
-.. code::
+.. code:: none
 
   LD_PRELOAD=`pwd`/scudo-allocator.so ./a.out
 
 Options
 -------
 Several aspects of the allocator can be configured through the following ways:
 
 - by defining a ``__scudo_default_options`` function in one's program that
   returns the options string to be parsed. Said function must have the following
   prototype: ``extern "C" const char* __scudo_default_options()``.
 
 - through the environment variable SCUDO_OPTIONS, containing the options string
   to be parsed. Options defined this way will override any definition made
   through ``__scudo_default_options``;
 
 The options string follows a syntax similar to ASan, where distinct options
 can be assigned in the same string, separated by colons.
 
 For example, using the environment variable:
 
-.. code::
+.. code:: none
 
-  SCUDO_OPTIONS="DeleteSizeMismatch=1:QuarantineSizeMb=16" ./a.out
+  SCUDO_OPTIONS="DeleteSizeMismatch=1:QuarantineSizeKb=64" ./a.out
 
 Or using the function:
 
-.. code::
+.. code:: cpp
 
   extern "C" const char *__scudo_default_options() {
-    return "DeleteSizeMismatch=1:QuarantineSizeMb=16";
+    return "DeleteSizeMismatch=1:QuarantineSizeKb=64";
   }
 
 
 The following options are available:
 
 +-----------------------------+----------------+----------------+------------------------------------------------+
 | Option                      | 64-bit default | 32-bit default | Description                                    |
 +-----------------------------+----------------+----------------+------------------------------------------------+
-| QuarantineSizeMb            | 64             | 16             | The size (in Mb) of quarantine used to delay   |
+| QuarantineSizeKb            | 256            | 64             | The size (in Mb) of quarantine used to delay   |
 |                             |                |                | the actual deallocation of chunks. Lower value |
 |                             |                |                | may reduce memory usage but decrease the       |
 |                             |                |                | effectiveness of the mitigation; a negative    |
 |                             |                |                | value will fallback to a default of 64Mb.      |
 +-----------------------------+----------------+----------------+------------------------------------------------+
+| QuarantineChunksUpToSize    | 2048           | 512            | The maximum size (in bytes) of chunks to be    |
+|                             |                |                | quarantined. Lower value may reduce memory     |
+|                             |                |                | usage but decrease the effectiveness of the    |
+|                             |                |                | mitigation.                                    |
++-----------------------------+----------------+----------------+------------------------------------------------+
 | ThreadLocalQuarantineSizeKb | 1024           | 256            | The size (in Kb) of per-thread cache use to    |
 |                             |                |                | offload the global quarantine. Lower value may |
 |                             |                |                | reduce memory usage but might increase         |
 |                             |                |                | contention on the global quarantine.           |
 +-----------------------------+----------------+----------------+------------------------------------------------+
 | DeallocationTypeMismatch    | true           | true           | Whether or not we report errors on             |
 |                             |                |                | malloc/delete, new/free, new/delete[], etc.    |
 +-----------------------------+----------------+----------------+------------------------------------------------+