1 /* Copyright (c) 2015-2019. The SimGrid Team. All rights reserved. */
3 /* This program is free software; you can redistribute it and/or modify it
4 * under the terms of the license (GNU LGPL) which comes with this package. */
8 #define MAP_POPULATE MAP_PREFAULT_READ
11 #include "src/internal_config.h"
13 #include "xbt/sysdep.h"
15 #include "src/mc/sosp/PageStore.hpp"
16 #include "src/mc/mc_mmu.hpp"
18 #include <cstring> // memcpy, memcmp
21 XBT_LOG_NEW_DEFAULT_SUBCATEGORY(mc_page_snapshot, mc, "Logging specific to mc_page_snapshot");
26 /** @brief Compute a hash for the given memory page
28 * The page is used before inserting the page in the page store
29 * in order to find duplicate of this page in the page store.
31 * @param data Memory page
32 * @return hash off the page
34 static XBT_ALWAYS_INLINE PageStore::hash_type mc_hash_page(const void* data)
36 const std::uint64_t* values = (const uint64_t*)data;
37 std::size_t n = xbt_pagesize / sizeof(uint64_t);
40 std::uint64_t hash = 5381;
41 for (std::size_t i = 0; i != n; ++i)
42 hash = ((hash << 5) + hash) + values[i];
46 // ***** snapshot_page_manager
48 PageStore::PageStore(std::size_t size) : memory_(nullptr), capacity_(size), top_index_(0)
50 // Using mmap in order to be able to expand the region by relocating it somewhere else in the virtual memory space:
52 ::mmap(nullptr, size << xbt_pagebits, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS | MAP_POPULATE, -1, 0);
53 if (memory == MAP_FAILED)
54 xbt_die("Could not mmap initial snapshot pages.");
57 this->memory_ = memory;
58 this->page_counts_.resize(size);
61 PageStore::~PageStore()
63 ::munmap(this->memory_, this->capacity_ << xbt_pagebits);
66 void PageStore::resize(std::size_t size)
68 size_t old_bytesize = this->capacity_ << xbt_pagebits;
69 size_t new_bytesize = size << xbt_pagebits;
72 // Expand the memory region by moving it into another
73 // virtual memory address if necessary:
75 new_memory = mremap(this->memory_, old_bytesize, new_bytesize, MREMAP_MAYMOVE);
76 if (new_memory == MAP_FAILED)
77 xbt_die("Could not mremap snapshot pages.");
79 if (new_bytesize > old_bytesize) {
80 // Grow: first try to add new space after current map
81 new_memory = mmap((char*)this->memory_ + old_bytesize, new_bytesize - old_bytesize, PROT_READ | PROT_WRITE,
82 MAP_PRIVATE | MAP_ANONYMOUS | MAP_POPULATE, -1, 0);
83 if (new_memory == MAP_FAILED)
84 xbt_die("Could not mremap snapshot pages.");
85 // Check if expanding worked
86 if (new_memory != (char*)this->memory_ + old_bytesize) {
87 // New memory segment could not be put at the end of this->memory_,
88 // so cancel this one and try to rellocate everything and copy data
89 munmap(new_memory, new_bytesize - old_bytesize);
91 mmap(nullptr, new_bytesize, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS | MAP_POPULATE, -1, 0);
92 if (new_memory == MAP_FAILED)
93 xbt_die("Could not mremap snapshot pages.");
94 memcpy(new_memory, this->memory_, old_bytesize);
95 munmap(this->memory_, old_bytesize);
98 // We don't have functions to shrink a mapping, so leave memory as
100 new_memory = this->memory_;
104 this->capacity_ = size;
105 this->memory_ = new_memory;
106 this->page_counts_.resize(size, 0);
109 /** Allocate a free page
111 * @return index of the free page
113 std::size_t PageStore::alloc_page()
115 if (this->free_pages_.empty()) {
117 // Expand the region:
118 if (this->top_index_ == this->capacity_)
119 // All the pages are allocated, we need add more pages:
120 this->resize(2 * this->capacity_);
122 // Use a page from the top:
123 return this->top_index_++;
127 // Use a page from free_pages_ (inside of the region):
128 size_t res = this->free_pages_[this->free_pages_.size() - 1];
129 this->free_pages_.pop_back();
134 void PageStore::remove_page(std::size_t pageno)
136 this->free_pages_.push_back(pageno);
137 const void* page = this->get_page(pageno);
138 hash_type hash = mc_hash_page(page);
139 this->hash_index_[hash].erase(pageno);
142 /** Store a page in memory */
143 std::size_t PageStore::store_page(void* page)
145 xbt_assert(top_index_ <= this->capacity_, "top_index is not consistent");
147 // First, we check if a page with the same content is already in the page store:
148 // 1. compute the hash of the page
149 // 2. find pages with the same hash using `hash_index_`
150 // 3. find a page with the same content
151 hash_type hash = mc_hash_page(page);
153 // Try to find a duplicate in set of pages with the same hash:
154 page_set_type& page_set = this->hash_index_[hash];
155 for (size_t const& pageno : page_set) {
156 const void* snapshot_page = this->get_page(pageno);
157 if (memcmp(page, snapshot_page, xbt_pagesize) == 0) {
159 // If a page with the same content is already in the page store it's reused and its refcount is incremented.
160 page_counts_[pageno]++;
165 // Otherwise, a new page is allocated in the page store and the content of the page is `memcpy()`-ed to this new page.
166 std::size_t pageno = alloc_page();
167 xbt_assert(this->page_counts_[pageno] == 0, "Allocated page is already used");
168 void* snapshot_page = (void*)this->get_page(pageno);
169 memcpy(snapshot_page, page, xbt_pagesize);
170 page_set.insert(pageno);
171 page_counts_[pageno]++;
176 } // namespace simgrid