1 /* Copyright (c) 2015. The SimGrid Team.
2 * All rights reserved. */
4 /* This program is free software; you can redistribute it and/or modify it
5 * under the terms of the license (GNU LGPL) which comes with this package. */
8 #include <string.h> // memcpy, memcmp
12 # define MAP_POPULATE MAP_PREFAULT_READ
17 #include <xbt/sysdep.h>
19 #include "src/internal_config.h"
21 #include "src/mc/PageStore.hpp"
23 #include "src/mc/mc_mmu.h"
25 XBT_LOG_NEW_DEFAULT_SUBCATEGORY(mc_page_snapshot, mc,
26 "Logging specific to mc_page_snapshot");
31 /** @brief Compute a hash for the given memory page
33 * The page is used before inserting the page in the page store
34 * in order to find duplicate of this page in the page store.
36 * @param data Memory page
37 * @return hash off the page
39 static inline __attribute__ ((always_inline))
40 PageStore::hash_type mc_hash_page(const void* data)
42 const std::uint64_t* values = (const uint64_t*) data;
43 std::size_t n = xbt_pagesize / sizeof(uint64_t);
46 std::uint64_t hash = 5381;
47 for (std::size_t i = 0; i != n; ++i)
48 hash = ((hash << 5) + hash) + values[i];
52 // ***** snapshot_page_manager
54 PageStore::PageStore(size_t size) :
55 memory_(nullptr), capacity_(0), top_index_(0)
57 // Using mmap in order to be able to expand the region
58 // by relocating it somewhere else in the virtual memory
60 void* memory = ::mmap(nullptr, size << xbt_pagebits, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS|MAP_POPULATE, -1, 0);
61 if (memory == MAP_FAILED)
62 xbt_die("Could not mmap initial snapshot pages.");
65 this->capacity_ = size;
66 this->memory_ = memory;
67 this->page_counts_.resize(size);
70 PageStore::~PageStore()
72 ::munmap(this->memory_, this->capacity_ << xbt_pagebits);
75 void PageStore::resize(std::size_t size)
77 size_t old_bytesize = this->capacity_ << xbt_pagebits;
78 size_t new_bytesize = size << xbt_pagebits;
81 // Expand the memory region by moving it into another
82 // virtual memory address if necessary:
84 new_memory = mremap(this->memory_, old_bytesize, new_bytesize, MREMAP_MAYMOVE);
85 if (new_memory == MAP_FAILED)
86 xbt_die("Could not mremap snapshot pages.");
88 if (new_bytesize > old_bytesize) {
89 // Grow: first try to add new space after current map
90 new_memory = mmap((char *)this->memory_ + old_bytesize,
91 new_bytesize-old_bytesize,
93 MAP_PRIVATE|MAP_ANONYMOUS|MAP_POPULATE,
95 if (new_memory == MAP_FAILED)
96 xbt_die("Could not mremap snapshot pages.");
97 // Check if expanding worked
98 if (new_memory != (char *)this->memory_ + old_bytesize) {
99 // New memory segment could not be put at the end of this->memory_,
100 // so cancel this one and try to rellocate everything and copy data
101 munmap(new_memory, new_bytesize-old_bytesize);
102 new_memory = mmap(nullptr,
104 PROT_READ|PROT_WRITE,
105 MAP_PRIVATE|MAP_ANONYMOUS|MAP_POPULATE,
107 if (new_memory == MAP_FAILED)
108 xbt_die("Could not mremap snapshot pages.");
109 memcpy(new_memory, this->memory_, old_bytesize);
110 munmap(this->memory_, old_bytesize);
114 // We don't have functions to shrink a mapping, so leave memory as
116 new_memory = this->memory_;
120 this->capacity_ = size;
121 this->memory_ = new_memory;
122 this->page_counts_.resize(size, 0);
125 /** Allocate a free page
127 * @return index of the free page
129 std::size_t PageStore::alloc_page()
131 if (this->free_pages_.empty()) {
133 // Expand the region:
134 if (this->top_index_ == this->capacity_)
135 // All the pages are allocated, we need add more pages:
136 this->resize(2 * this->capacity_);
138 // Use a page from the top:
139 return this->top_index_++;
143 // Use a page from free_pages_ (inside of the region):
144 size_t res = this->free_pages_[this->free_pages_.size() - 1];
145 this->free_pages_.pop_back();
151 void PageStore::remove_page(std::size_t pageno)
153 this->free_pages_.push_back(pageno);
154 const void* page = this->get_page(pageno);
155 hash_type hash = mc_hash_page(page);
156 this->hash_index_[hash].erase(pageno);
159 /** Store a page in memory */
160 std::size_t PageStore::store_page(void* page)
162 xbt_assert(top_index_ <= this->capacity_, "top_index is not consistent");
164 // First, we check if a page with the same content is already in the page
166 // 1. compute the hash of the page;
167 // 2. find pages with the same hash using `hash_index_`;
168 // 3. find a page with the same content.
169 hash_type hash = mc_hash_page(page);
171 // Try to find a duplicate in set of pages with the same hash:
172 page_set_type& page_set = this->hash_index_[hash];
173 for (size_t pageno : page_set) {
174 const void* snapshot_page = this->get_page(pageno);
175 if (memcmp(page, snapshot_page, xbt_pagesize) == 0) {
177 // If a page with the same content is already in the page store it is
178 // reused and its reference count is incremented.
179 page_counts_[pageno]++;
185 // Otherwise, a new page is allocated in the page store and the content
186 // of the page is `memcpy()`-ed to this new page.
187 std::size_t pageno = alloc_page();
188 xbt_assert(this->page_counts_[pageno]==0, "Allocated page is already used");
189 void* snapshot_page = (void*) this->get_page(pageno);
190 memcpy(snapshot_page, page, xbt_pagesize);
191 page_set.insert(pageno);
192 page_counts_[pageno]++;
205 #include <sys/mman.h>
209 #include "src/mc/PageStore.hpp"
211 static int value = 0;
213 static void new_content(void* data, std::size_t size)
215 ::memset(data, ++value, size);
218 static void* getpage()
220 return mmap(nullptr, getpagesize(), PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
223 XBT_TEST_SUITE("mc_page_store", "Page store");
225 XBT_TEST_UNIT("base", test_mc_page_store, "Test adding/removing pages in the store")
227 using simgrid::mc::PageStore;
229 xbt_test_add("Init");
230 std::size_t pagesize = (size_t) getpagesize();
231 std::unique_ptr<PageStore> store
232 = std::unique_ptr<PageStore>(new simgrid::mc::PageStore(500));
233 void* data = getpage();
234 xbt_test_assert(store->size()==0, "Bad size");
236 xbt_test_add("Store the page once");
237 new_content(data, pagesize);
238 size_t pageno1 = store->store_page(data);
239 xbt_test_assert(store->get_ref(pageno1)==1, "Bad refcount");
240 const void* copy = store->get_page(pageno1);
241 xbt_test_assert(::memcmp(data, copy, pagesize)==0, "Page data should be the same");
242 xbt_test_assert(store->size()==1, "Bad size");
244 xbt_test_add("Store the same page again");
245 size_t pageno2 = store->store_page(data);
246 xbt_test_assert(pageno1==pageno2, "Page should be the same");
247 xbt_test_assert(store->get_ref(pageno1)==2, "Bad refcount");
248 xbt_test_assert(store->size()==1, "Bad size");
250 xbt_test_add("Store a new page");
251 new_content(data, pagesize);
252 size_t pageno3 = store->store_page(data);
253 xbt_test_assert(pageno1 != pageno3, "New page should be different");
254 xbt_test_assert(store->size()==2, "Bad size");
256 xbt_test_add("Unref pages");
257 store->unref_page(pageno1);
258 xbt_assert(store->get_ref(pageno1)==1, "Bad refcount");
259 xbt_assert(store->size()==2, "Bad size");
260 store->unref_page(pageno2);
261 xbt_test_assert(store->size()==1, "Bad size");
263 xbt_test_add("Reallocate page");
264 new_content(data, pagesize);
265 size_t pageno4 = store->store_page(data);
266 xbt_test_assert(pageno1 == pageno4, "Page was not reused");
267 xbt_test_assert(store->get_ref(pageno4)==1, "Bad refcount");
268 xbt_test_assert(store->size()==2, "Bad size");
271 #endif /* SIMGRID_TEST */