area is mapped on a 1MiB file on disk. If the returned bloc is of size
N MiB, then the same file is mapped N times to cover the whole bloc.
At the end, no matter how many SMPI_SHARED_MALLOC you do, this will
-only consume 1 MiB in memory.
+only consume 1 MiB in memory.
You can disable this behavior and come back to regular mallocs (for
example for debugging purposes) using \c "no" as a value.
+If you want to keep private some parts of the buffer, for instance if these
+parts are used by the application logic and should not be corrupted, you
+can use SMPI_PARTIAL_SHARED_MALLOC(size, offsets, offsets_count).
+
+As an example,
+
+\code{.C}
+ mem = SMPI_PARTIAL_SHARED_MALLOC(500, {27,42 , 100,200}, 2);
+\endcode
+
+will allocate 500 bytes to mem, such that mem[27..41] and mem[100..199]
+are shared and other area remain private.
+
+Then, it can be deallocated by calling SMPI_SHARED_FREE(mem).
+
+When smpi/shared-malloc:global is used, the memory consumption problem
+is solved, but it may induce too much load on the kernel's pages table.
+In this case, you should use huge pages so that we create only one
+entry per Mb of malloced data instead of one entry per 4k.
+To activate this, you must mount a hugetlbfs on your system and allocate
+at least one huge page:
+
+\code{.sh}
+ mkdir /home/huge
+ sudo mount none /home/huge -t hugetlbfs -o rw,mode=0777
+ sudo sh -c 'echo 1 > /proc/sys/vm/nr_hugepages' # echo more if you need more
+\endcode
+
+Then, you can pass the option --cfg=smpi/shared-malloc-hugepage:/home/huge
+to smpirun to actually activate the huge page support in shared mallocs.
+
\subsection options_model_smpi_wtime smpi/wtime: Inject constant times for calls to MPI_Wtime
\b Default value: 0
- \c smpi/privatization: \ref options_smpi_privatization
- \c smpi/send-is-detached-thresh: \ref options_model_smpi_detached
- \c smpi/shared-malloc: \ref options_model_smpi_shared_malloc
+- \c smpi/shared-malloc-hugepage: \ref options_model_smpi_shared_malloc
- \c smpi/simulate-computation: \ref options_smpi_bench
- \c smpi/test: \ref options_model_smpi_test
- \c smpi/wtime: \ref options_model_smpi_wtime
