[mc] Fix mc_translate_address_region() for per-page snapshots

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

diff --git a/src/mc/mc_page_store.cpp b/src/mc/mc_page_store.cpp
index b91af86..467ade6 100644 (file)
--- a/src/mc/mc_page_store.cpp
+++ b/src/mc/mc_page_store.cpp
@@ -55,7 +55,7 @@ s_mc_pages_store::s_mc_pages_store(size_t size) :
   // Using mmap in order to be able to expand the region
   // by relocating it somewhere else in the virtual memory
   // space:
-  void * memory = ::mmap(NULL, size << xbt_pagebits, PROT_READ|PROT_WRITE, MAP_SHARED|MAP_ANONYMOUS|MAP_POPULATE, -1, 0);
+  void * memory = ::mmap(NULL, size << xbt_pagebits, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS|MAP_POPULATE, -1, 0);
   if (memory==MAP_FAILED) {
     xbt_die("Could not mmap initial snapshot pages.");
   }
@@ -73,18 +73,19 @@ s_mc_pages_store::~s_mc_pages_store()
 
 void s_mc_pages_store::resize(size_t size)
 {
+  size_t old_bytesize = this->capacity_ << xbt_pagebits;
   size_t new_bytesize = size << xbt_pagebits;
 
   // Expand the memory region by moving it into another
   // virtual memory address if necessary:
-  void* new_memory = mremap(this->memory_, this->capacity_ << xbt_pagesize, new_bytesize, MREMAP_MAYMOVE);
+  void* new_memory = mremap(this->memory_, old_bytesize, new_bytesize, MREMAP_MAYMOVE);
   if (new_memory == MAP_FAILED) {
     xbt_die("Could not mremap snapshot pages.");
   }
 
   this->capacity_ = size;
   this->memory_ = new_memory;
-  this->page_counts_.resize(size);
+  this->page_counts_.resize(size, 0);
 }
 
 /** Allocate a free page
@@ -96,7 +97,7 @@ size_t s_mc_pages_store::alloc_page()
   if (this->free_pages_.empty()) {
 
     // Expand the region:
-    if (top_index_ == this->capacity_) {
+    if (this->top_index_ == this->capacity_) {
       // All the pages are allocated, we need add more pages:
       this->resize(2 * this->capacity_);
     }
@@ -128,19 +129,27 @@ size_t s_mc_pages_store::store_page(void* page)
   xbt_assert(mc_page_offset(page)==0, "Not at the beginning of a page");
   xbt_assert(top_index_ <= this->capacity_, "top_index is not consistent");
 
-  // Search the page in the snapshot pages:
+  // First, we check if a page with the same content is already in the page
+  // store:
+  //  1. compute the hash of the page;
+  //  2. find pages with the same hash using `hash_index_`;
+  //  3. find a page with the same content.
   uint64_t hash = mc_hash_page(page);
   page_set_type& page_set = this->hash_index_[hash];
   BOOST_FOREACH (size_t pageno, page_set) {
     const void* snapshot_page = this->get_page(pageno);
     if (memcmp(page, snapshot_page, xbt_pagesize) == 0) {
-      // Page found, reuse it:
+
+      // If a page with the same content is already in the page store it is
+      // reused and its reference count is incremented.
       page_counts_[pageno]++;
       return pageno;
+
     }
   }
 
-  // Allocate a new page for this page:
+  // Otherwise, a new page is allocated in the page store and the content
+  // of the page is `memcpy()`-ed to this new page.
   size_t pageno = alloc_page();
   void* snapshot_page = (void*) this->get_page(pageno);
   memcpy(snapshot_page, page, xbt_pagesize);
@@ -153,6 +162,11 @@ size_t s_mc_pages_store::store_page(void* page)
 
 extern "C" {
 
+const void* mc_page_store_get_page(mc_pages_store_t page_store, size_t pageno)
+{
+  return page_store->get_page(pageno);
+}
+
 mc_pages_store_t mc_pages_store_new()
 {
   return new s_mc_pages_store_t(500);