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 XBT_ALWAYS_INLINE PageStore::hash_type mc_hash_page(const void* data)
41 const std::uint64_t* values = (const uint64_t*) data;
42 std::size_t n = xbt_pagesize / sizeof(uint64_t);
45 std::uint64_t hash = 5381;
46 for (std::size_t i = 0; i != n; ++i)
47 hash = ((hash << 5) + hash) + values[i];
51 // ***** snapshot_page_manager
53 PageStore::PageStore(size_t size) :
54 memory_(nullptr), capacity_(0), top_index_(0)
56 // Using mmap in order to be able to expand the region
57 // by relocating it somewhere else in the virtual memory
59 void* memory = ::mmap(nullptr, size << xbt_pagebits, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS|MAP_POPULATE, -1, 0);
60 if (memory == MAP_FAILED)
61 xbt_die("Could not mmap initial snapshot pages.");
64 this->capacity_ = size;
65 this->memory_ = memory;
66 this->page_counts_.resize(size);
69 PageStore::~PageStore()
71 ::munmap(this->memory_, this->capacity_ << xbt_pagebits);
74 void PageStore::resize(std::size_t size)
76 size_t old_bytesize = this->capacity_ << xbt_pagebits;
77 size_t new_bytesize = size << xbt_pagebits;
80 // Expand the memory region by moving it into another
81 // virtual memory address if necessary:
83 new_memory = mremap(this->memory_, old_bytesize, new_bytesize, MREMAP_MAYMOVE);
84 if (new_memory == MAP_FAILED)
85 xbt_die("Could not mremap snapshot pages.");
87 if (new_bytesize > old_bytesize) {
88 // Grow: first try to add new space after current map
89 new_memory = mmap((char *)this->memory_ + old_bytesize,
90 new_bytesize-old_bytesize,
92 MAP_PRIVATE|MAP_ANONYMOUS|MAP_POPULATE,
94 if (new_memory == MAP_FAILED)
95 xbt_die("Could not mremap snapshot pages.");
96 // Check if expanding worked
97 if (new_memory != (char *)this->memory_ + old_bytesize) {
98 // New memory segment could not be put at the end of this->memory_,
99 // so cancel this one and try to rellocate everything and copy data
100 munmap(new_memory, new_bytesize-old_bytesize);
101 new_memory = mmap(nullptr,
103 PROT_READ|PROT_WRITE,
104 MAP_PRIVATE|MAP_ANONYMOUS|MAP_POPULATE,
106 if (new_memory == MAP_FAILED)
107 xbt_die("Could not mremap snapshot pages.");
108 memcpy(new_memory, this->memory_, old_bytesize);
109 munmap(this->memory_, old_bytesize);
113 // We don't have functions to shrink a mapping, so leave memory as
115 new_memory = this->memory_;
119 this->capacity_ = size;
120 this->memory_ = new_memory;
121 this->page_counts_.resize(size, 0);
124 /** Allocate a free page
126 * @return index of the free page
128 std::size_t PageStore::alloc_page()
130 if (this->free_pages_.empty()) {
132 // Expand the region:
133 if (this->top_index_ == this->capacity_)
134 // All the pages are allocated, we need add more pages:
135 this->resize(2 * this->capacity_);
137 // Use a page from the top:
138 return this->top_index_++;
142 // Use a page from free_pages_ (inside of the region):
143 size_t res = this->free_pages_[this->free_pages_.size() - 1];
144 this->free_pages_.pop_back();
150 void PageStore::remove_page(std::size_t pageno)
152 this->free_pages_.push_back(pageno);
153 const void* page = this->get_page(pageno);
154 hash_type hash = mc_hash_page(page);
155 this->hash_index_[hash].erase(pageno);
158 /** Store a page in memory */
159 std::size_t PageStore::store_page(void* page)
161 xbt_assert(top_index_ <= this->capacity_, "top_index is not consistent");
163 // First, we check if a page with the same content is already in the page
165 // 1. compute the hash of the page;
166 // 2. find pages with the same hash using `hash_index_`;
167 // 3. find a page with the same content.
168 hash_type hash = mc_hash_page(page);
170 // Try to find a duplicate in set of pages with the same hash:
171 page_set_type& page_set = this->hash_index_[hash];
172 for (size_t pageno : page_set) {
173 const void* snapshot_page = this->get_page(pageno);
174 if (memcmp(page, snapshot_page, xbt_pagesize) == 0) {
176 // If a page with the same content is already in the page store it is
177 // reused and its reference count is incremented.
178 page_counts_[pageno]++;
184 // Otherwise, a new page is allocated in the page store and the content
185 // of the page is `memcpy()`-ed to this new page.
186 std::size_t pageno = alloc_page();
187 xbt_assert(this->page_counts_[pageno]==0, "Allocated page is already used");
188 void* snapshot_page = (void*) this->get_page(pageno);
189 memcpy(snapshot_page, page, xbt_pagesize);
190 page_set.insert(pageno);
191 page_counts_[pageno]++;
204 #include <sys/mman.h>
208 #include "src/mc/PageStore.hpp"
210 static int value = 0;
212 static void new_content(void* data, std::size_t size)
214 ::memset(data, ++value, size);
217 static void* getpage()
219 return mmap(nullptr, getpagesize(), PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
222 XBT_TEST_SUITE("mc_page_store", "Page store");
224 XBT_TEST_UNIT("base", test_mc_page_store, "Test adding/removing pages in the store")
226 using simgrid::mc::PageStore;
228 xbt_test_add("Init");
229 std::size_t pagesize = (size_t) getpagesize();
230 std::unique_ptr<PageStore> store
231 = std::unique_ptr<PageStore>(new simgrid::mc::PageStore(500));
232 void* data = getpage();
233 xbt_test_assert(store->size()==0, "Bad size");
235 xbt_test_add("Store the page once");
236 new_content(data, pagesize);
237 size_t pageno1 = store->store_page(data);
238 xbt_test_assert(store->get_ref(pageno1)==1, "Bad refcount");
239 const void* copy = store->get_page(pageno1);
240 xbt_test_assert(::memcmp(data, copy, pagesize)==0, "Page data should be the same");
241 xbt_test_assert(store->size()==1, "Bad size");
243 xbt_test_add("Store the same page again");
244 size_t pageno2 = store->store_page(data);
245 xbt_test_assert(pageno1==pageno2, "Page should be the same");
246 xbt_test_assert(store->get_ref(pageno1)==2, "Bad refcount");
247 xbt_test_assert(store->size()==1, "Bad size");
249 xbt_test_add("Store a new page");
250 new_content(data, pagesize);
251 size_t pageno3 = store->store_page(data);
252 xbt_test_assert(pageno1 != pageno3, "New page should be different");
253 xbt_test_assert(store->size()==2, "Bad size");
255 xbt_test_add("Unref pages");
256 store->unref_page(pageno1);
257 xbt_assert(store->get_ref(pageno1)==1, "Bad refcount");
258 xbt_assert(store->size()==2, "Bad size");
259 store->unref_page(pageno2);
260 xbt_test_assert(store->size()==1, "Bad size");
262 xbt_test_add("Reallocate page");
263 new_content(data, pagesize);
264 size_t pageno4 = store->store_page(data);
265 xbt_test_assert(pageno1 == pageno4, "Page was not reused");
266 xbt_test_assert(store->get_ref(pageno4)==1, "Bad refcount");
267 xbt_test_assert(store->size()==2, "Bad size");
270 #endif /* SIMGRID_TEST */