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"
16 #include "src/include/xxhash.hpp"
18 #include "src/mc/mc_mmu.hpp"
19 #include "src/mc/sosp/PageStore.hpp"
21 #include <cstring> // memcpy, memcmp
24 XBT_LOG_NEW_DEFAULT_SUBCATEGORY(mc_page_snapshot, mc, "Logging specific to mc_page_snapshot");
29 /** @brief Compute a hash for the given memory page
31 * The page is used before inserting the page in the page store
32 * in order to find duplicate of this page in the page store.
34 * @param data Memory page
35 * @return hash off the page
37 static XBT_ALWAYS_INLINE PageStore::hash_type mc_hash_page(const void* data)
40 return xxh::xxhash<64>(data, xbt_pagesize);
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];
53 // ***** snapshot_page_manager
55 PageStore::PageStore(std::size_t size) : memory_(nullptr), capacity_(size), top_index_(0)
57 // Using mmap in order to be able to expand the region by relocating it somewhere else in the virtual memory space:
59 ::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->memory_ = memory;
65 this->page_counts_.resize(size);
68 PageStore::~PageStore()
70 ::munmap(this->memory_, this->capacity_ << xbt_pagebits);
73 void PageStore::resize(std::size_t size)
75 size_t old_bytesize = this->capacity_ << xbt_pagebits;
76 size_t new_bytesize = size << xbt_pagebits;
79 // Expand the memory region by moving it into another
80 // virtual memory address if necessary:
82 new_memory = mremap(this->memory_, old_bytesize, new_bytesize, MREMAP_MAYMOVE);
83 if (new_memory == MAP_FAILED)
84 xbt_die("Could not mremap snapshot pages.");
86 if (new_bytesize > old_bytesize) {
87 // Grow: first try to add new space after current map
88 new_memory = mmap((char*)this->memory_ + old_bytesize, new_bytesize - old_bytesize, PROT_READ | PROT_WRITE,
89 MAP_PRIVATE | MAP_ANONYMOUS | MAP_POPULATE, -1, 0);
90 if (new_memory == MAP_FAILED)
91 xbt_die("Could not mremap snapshot pages.");
92 // Check if expanding worked
93 if (new_memory != (char*)this->memory_ + old_bytesize) {
94 // New memory segment could not be put at the end of this->memory_,
95 // so cancel this one and try to rellocate everything and copy data
96 munmap(new_memory, new_bytesize - old_bytesize);
98 mmap(nullptr, new_bytesize, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS | MAP_POPULATE, -1, 0);
99 if (new_memory == MAP_FAILED)
100 xbt_die("Could not mremap snapshot pages.");
101 memcpy(new_memory, this->memory_, old_bytesize);
102 munmap(this->memory_, old_bytesize);
105 // We don't have functions to shrink a mapping, so leave memory as
107 new_memory = this->memory_;
111 this->capacity_ = size;
112 this->memory_ = new_memory;
113 this->page_counts_.resize(size, 0);
116 /** Allocate a free page
118 * @return index of the free page
120 std::size_t PageStore::alloc_page()
122 if (this->free_pages_.empty()) {
124 // Expand the region:
125 if (this->top_index_ == this->capacity_)
126 // All the pages are allocated, we need add more pages:
127 this->resize(2 * this->capacity_);
129 // Use a page from the top:
130 return this->top_index_++;
134 // Use a page from free_pages_ (inside of the region):
135 size_t res = this->free_pages_[this->free_pages_.size() - 1];
136 this->free_pages_.pop_back();
141 void PageStore::remove_page(std::size_t pageno)
143 this->free_pages_.push_back(pageno);
144 const void* page = this->get_page(pageno);
145 hash_type hash = mc_hash_page(page);
146 this->hash_index_[hash].erase(pageno);
149 /** Store a page in memory */
150 std::size_t PageStore::store_page(void* page)
152 xbt_assert(top_index_ <= this->capacity_, "top_index is not consistent");
154 // First, we check if a page with the same content is already in the page store:
155 // 1. compute the hash of the page
156 // 2. find pages with the same hash using `hash_index_`
157 // 3. find a page with the same content
158 hash_type hash = mc_hash_page(page);
160 // Try to find a duplicate in set of pages with the same hash:
161 page_set_type& page_set = this->hash_index_[hash];
162 for (size_t const& pageno : page_set) {
163 const void* snapshot_page = this->get_page(pageno);
164 if (memcmp(page, snapshot_page, xbt_pagesize) == 0) {
166 // If a page with the same content is already in the page store it's reused and its refcount is incremented.
167 page_counts_[pageno]++;
172 // Otherwise, a new page is allocated in the page store and the content of the page is `memcpy()`-ed to this new page.
173 std::size_t pageno = alloc_page();
174 xbt_assert(this->page_counts_[pageno] == 0, "Allocated page is already used");
175 void* snapshot_page = (void*)this->get_page(pageno);
176 memcpy(snapshot_page, page, xbt_pagesize);
177 page_set.insert(pageno);
178 page_counts_[pageno]++;
183 } // namespace simgrid