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/include/xxhash.hpp"
16 #include "src/mc/mc_mmu.hpp"
17 #include "src/mc/sosp/PageStore.hpp"
19 #include <cstring> // memcpy, memcmp
22 XBT_LOG_NEW_DEFAULT_SUBCATEGORY(mc_page_snapshot, mc, "Logging specific to mc_page_snapshot");
27 /** @brief Compute a hash for the given memory page
29 * The page is used before inserting the page in the page store
30 * in order to find duplicate of this page in the page store.
32 * @param data Memory page
33 * @return hash off the page
35 static XBT_ALWAYS_INLINE PageStore::hash_type mc_hash_page(const void* data)
37 return xxh::xxhash<64>(data, xbt_pagesize);
40 // ***** snapshot_page_manager
42 PageStore::PageStore(std::size_t size) : memory_(nullptr), capacity_(size), top_index_(0)
44 // Using mmap in order to be able to expand the region by relocating it somewhere else in the virtual memory space:
46 ::mmap(nullptr, size << xbt_pagebits, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS | MAP_POPULATE, -1, 0);
47 if (memory == MAP_FAILED)
48 xbt_die("Could not mmap initial snapshot pages.");
51 this->memory_ = memory;
52 this->page_counts_.resize(size);
55 PageStore::~PageStore()
57 ::munmap(this->memory_, this->capacity_ << xbt_pagebits);
60 void PageStore::resize(std::size_t size)
62 size_t old_bytesize = this->capacity_ << xbt_pagebits;
63 size_t new_bytesize = size << xbt_pagebits;
66 // Expand the memory region by moving it into another
67 // virtual memory address if necessary:
69 new_memory = mremap(this->memory_, old_bytesize, new_bytesize, MREMAP_MAYMOVE);
70 if (new_memory == MAP_FAILED)
71 xbt_die("Could not mremap snapshot pages.");
73 if (new_bytesize > old_bytesize) {
74 // Grow: first try to add new space after current map
75 new_memory = mmap((char*)this->memory_ + old_bytesize, new_bytesize - old_bytesize, PROT_READ | PROT_WRITE,
76 MAP_PRIVATE | MAP_ANONYMOUS | MAP_POPULATE, -1, 0);
77 if (new_memory == MAP_FAILED)
78 xbt_die("Could not mremap snapshot pages.");
79 // Check if expanding worked
80 if (new_memory != (char*)this->memory_ + old_bytesize) {
81 // New memory segment could not be put at the end of this->memory_,
82 // so cancel this one and try to rellocate everything and copy data
83 munmap(new_memory, new_bytesize - old_bytesize);
85 mmap(nullptr, new_bytesize, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS | MAP_POPULATE, -1, 0);
86 if (new_memory == MAP_FAILED)
87 xbt_die("Could not mremap snapshot pages.");
88 memcpy(new_memory, this->memory_, old_bytesize);
89 munmap(this->memory_, old_bytesize);
92 // We don't have functions to shrink a mapping, so leave memory as
94 new_memory = this->memory_;
98 this->capacity_ = size;
99 this->memory_ = new_memory;
100 this->page_counts_.resize(size, 0);
103 /** Allocate a free page
105 * @return index of the free page
107 std::size_t PageStore::alloc_page()
109 if (this->free_pages_.empty()) {
111 // Expand the region:
112 if (this->top_index_ == this->capacity_)
113 // All the pages are allocated, we need add more pages:
114 this->resize(2 * this->capacity_);
116 // Use a page from the top:
117 return this->top_index_++;
121 // Use a page from free_pages_ (inside of the region):
122 size_t res = this->free_pages_[this->free_pages_.size() - 1];
123 this->free_pages_.pop_back();
128 void PageStore::remove_page(std::size_t pageno)
130 this->free_pages_.push_back(pageno);
131 const void* page = this->get_page(pageno);
132 hash_type hash = mc_hash_page(page);
133 this->hash_index_[hash].erase(pageno);
136 /** Store a page in memory */
137 std::size_t PageStore::store_page(void* page)
139 xbt_assert(top_index_ <= this->capacity_, "top_index is not consistent");
141 // First, we check if a page with the same content is already in the page store:
142 // 1. compute the hash of the page
143 // 2. find pages with the same hash using `hash_index_`
144 // 3. find a page with the same content
145 hash_type hash = mc_hash_page(page);
147 // Try to find a duplicate in set of pages with the same hash:
148 page_set_type& page_set = this->hash_index_[hash];
149 for (size_t const& pageno : page_set) {
150 const void* snapshot_page = this->get_page(pageno);
151 if (memcmp(page, snapshot_page, xbt_pagesize) == 0) {
153 // If a page with the same content is already in the page store it's reused and its refcount is incremented.
154 page_counts_[pageno]++;
159 // Otherwise, a new page is allocated in the page store and the content of the page is `memcpy()`-ed to this new page.
160 std::size_t pageno = alloc_page();
161 xbt_assert(this->page_counts_[pageno] == 0, "Allocated page is already used");
162 void* snapshot_page = (void*)this->get_page(pageno);
163 memcpy(snapshot_page, page, xbt_pagesize);
164 page_set.insert(pageno);
165 page_counts_[pageno]++;
170 } // namespace simgrid