update darshan modularization docs

ChangeLog

@@ -2,6 +2,16 @@
 Darshan Release Change Log
 --------------------------
 
+Darshan-3.0.0-pre2
+=============
+* add fix to install appropriate headers for linking external
+  applications with darshan-util (reported by Matthieu Dorier)
+* add darshan-util Ruby bindings for the new modularized version
+  of Darshan (3.0) (Matthieu Dorier)
+* add enhancement to darshan-runtime to allow per-module instrumentation
+  memory to be user configurable using a configure option or a runtime
+  environment variable
+
 Darshan-3.0.0-pre1
 =============
 * new version of Darshan with the following features/improvements:

darshan-runtime/doc/darshan-runtime.txt

@@ -57,6 +57,8 @@ will be placed.
 determine the log path at run time.
 * `--with-log-hints=`: specifies hints to use when writing the Darshan log
 file.  See `./configure --help` for details.
+* `--with-mod-mem=`: specifies the maximum amount of memory (in MiB) that
+each Darshan module can consume.
 * `--with-zlib=`: specifies an alternate location for the zlib development
 header and library.
 * `CC=`: specifies the MPI C compiler to use for compilation.
@@ -474,3 +476,4 @@ behavior at runtime:
 * DARSHAN_DISABLE_SHARED_REDUCTION: disables the step in Darshan aggregation in which files that were accessed by all ranks are collapsed into a single cumulative file record at rank 0.  This option retains more per-process information at the expense of creating larger log files. Note that it is up to individual instrumentation module implementations whether this environment variable is actually honored.
 * DARSHAN_LOGPATH: specifies the path to write Darshan log files to. Note that this directory needs to be formatted using the darshan-mk-log-dirs script.
 * DARSHAN_LOGFILE: specifies the path (directory + Darshan log file name) to write the output Darshan log to. This overrides the default Darshan behavior of automatically generating a log file name and adding it to a log file directory formatted using darshan-mk-log-dirs script.
+* DARSHAN_MODMEM: specifies the maximum amount of memory (in MiB) a Darshan instrumentation module can consume at runtime.

doc/darshan-modularization.txt

@@ -224,9 +224,10 @@ a module developer must provide to interface with the darshan-core runtime.
 * _my_rank_ is a pointer to an integer to store the calling process's application MPI rank in
 
 * _mod_mem_limit_ is a pointer to an integer which will store the amount of memory Darshan
-allows this module to use at runtime. Currently, `darshan-core` will hardcode this value to 2 MiB,
-but in the future this may be changed to optimize Darshan's memory footprint. Note that Darshan
-does not allocate any memory for modules, it just informs a module how much memory it can use.
+allows this module to use at runtime. Darshan's default module memory limit is currently set to
+2 MiB, but the user can choose a different value at configure time (using the `--with-mod-mem`
+configure option) or at runtime (using the DARSHAN_MODMEM environment variable). Note that Darshan
+does not allocate any memory for modules; it just informs a module how much memory it can use.
 
 * _sys_mem_alignment_ is a pointer to an integer which will store the system memory alignment value
 Darshan was configured with. This parameter may be set to `NULL` if a module is not concerned with the
@@ -248,8 +249,9 @@ any I/O data.
 void darshan_core_register_record(
     void *name,
     int len,
-    int printable_flag,
     darshan_module_id mod_id,
+    int printable_flag,
+    int mod_limit_flag,
     darshan_record_id *rec_id,
     int *file_alignment);
 
@@ -269,9 +271,13 @@ been previously registered.
 string length, but for nonprintable record names (e.g., an integer object identifier), this
 is the size of the record name type.
 
+* _mod_id_ is the identifier for the module attempting to register this record.
+
 * _printable_flag_ indicates whether the input record name is a printable ASCII string.
 
-* _mod_id_ is the identifier for the module attempting to register this record.
+* _mod_limit_flag_ indicates whether the calling module is out of memory to instrument new
+records or not. If this flag is set, darshan-core will not create new records and instead just
+search existing records for one corresponding to input _name_. 
 
 * _rec_id_ is a pointer to a variable which will store the unique record identifier generated
 by Darshan.