/** Store a page in memory */
size_t PageStore::store_page(void* page)
{
xbt_assert(top_index_ <= this->capacity_, "top_index is not consistent");
// 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.
hash_type hash = mc_hash_page(page);
// Try to find a duplicate in set of pages with the same hash:
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) {
// 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;
}
}
// 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();
xbt_assert(this->page_counts_[pageno]==0, "Allocated page is already used");
void* snapshot_page = (void*) this->get_page(pageno);
memcpy(snapshot_page, page, xbt_pagesize);
page_set.insert(pageno);
page_counts_[pageno]++;
return pageno;
}
void PageStore::remove_page(size_t pageno)
{
this->free_pages_.push_back(pageno);
const void* page = this->get_page(pageno);
hash_type hash = mc_hash_page(page);
#ifdef MC_PAGE_STORE_MD4
this->hash_index_.erase(hash);
#else
this->hash_index_[hash].erase(pageno);
#endif
}
