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
14 #include <xbt/sysdep.h>
16 #include "src/mc/PageStore.hpp"
18 #include "src/mc/mc_mmu.h"
20 XBT_LOG_NEW_DEFAULT_SUBCATEGORY(mc_page_snapshot, mc,
21 "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 inline __attribute__ ((always_inline))
35 PageStore::hash_type mc_hash_page(const void* data)
37 const std::uint64_t* values = (const uint64_t*) data;
38 std::size_t n = xbt_pagesize / sizeof(uint64_t);
41 std::uint64_t hash = 5381;
42 for (std::size_t i = 0; i != n; ++i)
43 hash = ((hash << 5) + hash) + values[i];
47 // ***** snapshot_page_manager
49 PageStore::PageStore(size_t size) :
50 memory_(nullptr), capacity_(0), top_index_(0)
52 // Using mmap in order to be able to expand the region
53 // by relocating it somewhere else in the virtual memory
55 void* memory = ::mmap(nullptr, size << xbt_pagebits, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS|MAP_POPULATE, -1, 0);
56 if (memory == MAP_FAILED)
57 xbt_die("Could not mmap initial snapshot pages.");
60 this->capacity_ = size;
61 this->memory_ = memory;
62 this->page_counts_.resize(size);
65 PageStore::~PageStore()
67 ::munmap(this->memory_, this->capacity_ << xbt_pagebits);
70 void PageStore::resize(std::size_t size)
72 size_t old_bytesize = this->capacity_ << xbt_pagebits;
73 size_t new_bytesize = size << xbt_pagebits;
75 // Expand the memory region by moving it into another
76 // virtual memory address if necessary:
77 void* new_memory = mremap(this->memory_, old_bytesize, new_bytesize, MREMAP_MAYMOVE);
78 if (new_memory == MAP_FAILED)
79 xbt_die("Could not mremap snapshot pages.");
81 this->capacity_ = size;
82 this->memory_ = new_memory;
83 this->page_counts_.resize(size, 0);
86 /** Allocate a free page
88 * @return index of the free page
90 std::size_t PageStore::alloc_page()
92 if (this->free_pages_.empty()) {
95 if (this->top_index_ == this->capacity_)
96 // All the pages are allocated, we need add more pages:
97 this->resize(2 * this->capacity_);
99 // Use a page from the top:
100 return this->top_index_++;
104 // Use a page from free_pages_ (inside of the region):
105 size_t res = this->free_pages_[this->free_pages_.size() - 1];
106 this->free_pages_.pop_back();
112 void PageStore::remove_page(std::size_t pageno)
114 this->free_pages_.push_back(pageno);
115 const void* page = this->get_page(pageno);
116 hash_type hash = mc_hash_page(page);
117 this->hash_index_[hash].erase(pageno);
120 /** Store a page in memory */
121 std::size_t PageStore::store_page(void* page)
123 xbt_assert(top_index_ <= this->capacity_, "top_index is not consistent");
125 // First, we check if a page with the same content is already in the page
127 // 1. compute the hash of the page;
128 // 2. find pages with the same hash using `hash_index_`;
129 // 3. find a page with the same content.
130 hash_type hash = mc_hash_page(page);
132 // Try to find a duplicate in set of pages with the same hash:
133 page_set_type& page_set = this->hash_index_[hash];
134 for (size_t pageno : page_set) {
135 const void* snapshot_page = this->get_page(pageno);
136 if (memcmp(page, snapshot_page, xbt_pagesize) == 0) {
138 // If a page with the same content is already in the page store it is
139 // reused and its reference count is incremented.
140 page_counts_[pageno]++;
146 // Otherwise, a new page is allocated in the page store and the content
147 // of the page is `memcpy()`-ed to this new page.
148 std::size_t pageno = alloc_page();
149 xbt_assert(this->page_counts_[pageno]==0, "Allocated page is already used");
150 void* snapshot_page = (void*) this->get_page(pageno);
151 memcpy(snapshot_page, page, xbt_pagesize);
152 page_set.insert(pageno);
153 page_counts_[pageno]++;
166 #include <sys/mman.h>
170 #include "src/mc/PageStore.hpp"
172 static int value = 0;
174 static void new_content(void* data, std::size_t size)
176 ::memset(data, ++value, size);
179 static void* getpage()
181 return mmap(nullptr, getpagesize(), PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
184 XBT_TEST_SUITE("mc_page_store", "Page store");
186 XBT_TEST_UNIT("base", test_mc_page_store, "Test adding/removing pages in the store")
188 using simgrid::mc::PageStore;
190 xbt_test_add("Init");
191 std::size_t pagesize = (size_t) getpagesize();
192 std::unique_ptr<PageStore> store
193 = std::unique_ptr<PageStore>(new simgrid::mc::PageStore(500));
194 void* data = getpage();
195 xbt_test_assert(store->size()==0, "Bad size");
197 xbt_test_add("Store the page once");
198 new_content(data, pagesize);
199 size_t pageno1 = store->store_page(data);
200 xbt_test_assert(store->get_ref(pageno1)==1, "Bad refcount");
201 const void* copy = store->get_page(pageno1);
202 xbt_test_assert(::memcmp(data, copy, pagesize)==0, "Page data should be the same");
203 xbt_test_assert(store->size()==1, "Bad size");
205 xbt_test_add("Store the same page again");
206 size_t pageno2 = store->store_page(data);
207 xbt_test_assert(pageno1==pageno2, "Page should be the same");
208 xbt_test_assert(store->get_ref(pageno1)==2, "Bad refcount");
209 xbt_test_assert(store->size()==1, "Bad size");
211 xbt_test_add("Store a new page");
212 new_content(data, pagesize);
213 size_t pageno3 = store->store_page(data);
214 xbt_test_assert(pageno1 != pageno3, "New page should be different");
215 xbt_test_assert(store->size()==2, "Bad size");
217 xbt_test_add("Unref pages");
218 store->unref_page(pageno1);
219 xbt_assert(store->get_ref(pageno1)==1, "Bad refcount");
220 xbt_assert(store->size()==2, "Bad size");
221 store->unref_page(pageno2);
222 xbt_test_assert(store->size()==1, "Bad size");
224 xbt_test_add("Reallocate page");
225 new_content(data, pagesize);
226 size_t pageno4 = store->store_page(data);
227 xbt_test_assert(pageno1 == pageno4, "Page was not reused");
228 xbt_test_assert(store->get_ref(pageno4)==1, "Bad refcount");
229 xbt_test_assert(store->size()==2, "Bad size");
232 #endif /* SIMGRID_TEST */