[mc] Documentation of mc_page_snapshot

[simgrid.git] / src / mc / mc_page_snapshot.cpp

diff --git a/src/mc/mc_page_snapshot.cpp b/src/mc/mc_page_snapshot.cpp
index c049b7d..2b905c0 100644 (file)
--- a/src/mc/mc_page_snapshot.cpp
+++ b/src/mc/mc_page_snapshot.cpp
@@ -10,13 +10,21 @@ extern "C" {
 
 // ***** Region management:
 
+/** @brief Take a per-page snapshot of a region
+ *
+ *  @param data            The start of the region (must be at the beginning of a page)
+ *  @param pag_count       Number of pages of the region
+ *  @param pagemap         Linux kernel pagemap values fot this region (or NULL)
+ *  @param reference_pages Snapshot page numbers of the previous soft_dirty_reset (or NULL)
+ *  @return                Snapshot page numbers of this new snapshot
+ */
 size_t* mc_take_page_snapshot_region(void* data, size_t page_count, uint64_t* pagemap, size_t* reference_pages)
 {
   size_t* pagenos = (size_t*) malloc(page_count * sizeof(size_t));
 
   for (size_t i=0; i!=page_count; ++i) {
     bool softclean = pagemap && !(pagemap[i] & SOFT_DIRTY);
-    if (softclean) {
+    if (softclean && reference_pages) {
       // The page is softclean, it is the same page as the reference page:
       pagenos[i] = reference_pages[i];
       mc_model_checker->pages->ref_page(reference_pages[i]);
@@ -38,6 +46,16 @@ void mc_free_page_snapshot_region(size_t* pagenos, size_t page_count)
   }
 }
 
+/** @brief Restore a snapshot of a region
+ *
+ *  If possible, the restoration will be incremental
+ *  (the modified pages will not be touched).
+ *
+ *  @param data            The start of the region (must be at the beginning of a page)
+ *  @param pag_count       Number of pages of the region
+ *  @param pagemap         Linux kernel pagemap values fot this region (or NULL)
+ *  @param reference_pages Snapshot page numbers of the previous soft_dirty_reset (or NULL)
+ */
 void mc_restore_page_snapshot_region(mc_mem_region_t region, size_t page_count, uint64_t* pagemap, mc_mem_region_t reference_region)
 {
   for (size_t i=0; i!=page_count; ++i) {
@@ -151,7 +169,7 @@ mc_mem_region_t mc_region_new_sparse(int type, void *start_addr, size_t size, mc
   size_t page_count = mc_page_count(size);
 
   uint64_t* pagemap = NULL;
-  if (mc_model_checker->parent_snapshot) {
+  if (_sg_mc_soft_dirty && mc_model_checker->parent_snapshot) {
       pagemap = (uint64_t*) mmalloc_no_memset((xbt_mheap_t) mc_heap, sizeof(uint64_t) * page_count);
       mc_read_pagemap(pagemap, mc_page_number(NULL, start_addr), page_count);
   }
@@ -175,7 +193,7 @@ void mc_region_restore_sparse(mc_mem_region_t reg, mc_mem_region_t ref_reg)
   uint64_t* pagemap = NULL;
 
   // Read soft-dirty bits if necessary in order to know which pages have changed:
-  if (mc_model_checker->parent_snapshot) {
+  if (_sg_mc_soft_dirty && mc_model_checker->parent_snapshot) {
     pagemap = (uint64_t*) mmalloc_no_memset((xbt_mheap_t) mc_heap, sizeof(uint64_t) * page_count);
     mc_read_pagemap(pagemap, mc_page_number(NULL, reg->start_addr), page_count);
   }