1 /* Copyright (c) 2015-2023. 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/3rd-party/xxhash.hpp"
16 #include "src/mc/mc_mmu.hpp"
17 #include "src/mc/sosp/PageStore.hpp"
19 #include <cstring> // memcpy, memcmp
22 namespace simgrid::mc {
24 /** @brief Compute a hash for the given memory page
26 * The page is used before inserting the page in the page store in order to find duplicate of this page in the page
29 * @param data Memory page
30 * @return hash off the page
32 static XBT_ALWAYS_INLINE PageStore::hash_type mc_hash_page(const void* data)
34 return xxh::xxhash<64>(data, xbt_pagesize);
37 // ***** snapshot_page_manager
39 PageStore::PageStore(std::size_t size) : capacity_(size)
41 // Using mmap in order to be able to expand the region by relocating it somewhere else in the virtual memory space:
43 ::mmap(nullptr, size << xbt_pagebits, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS | MAP_POPULATE, -1, 0);
44 xbt_assert(memory != MAP_FAILED, "Could not mmap initial snapshot pages.");
47 this->memory_ = memory;
48 this->page_counts_.resize(size);
51 PageStore::~PageStore()
53 ::munmap(this->memory_, this->capacity_ << xbt_pagebits);
56 void PageStore::resize(std::size_t size)
58 size_t old_bytesize = this->capacity_ << xbt_pagebits;
59 size_t new_bytesize = size << xbt_pagebits;
62 // Expand the memory region by moving it into another
63 // virtual memory address if necessary:
65 new_memory = mremap(this->memory_, old_bytesize, new_bytesize, MREMAP_MAYMOVE);
66 xbt_assert(new_memory != MAP_FAILED, "Could not mremap snapshot pages.");
68 if (new_bytesize > old_bytesize) {
69 // Grow: first try to add new space after current map
70 new_memory = mmap((char*)this->memory_ + old_bytesize, new_bytesize - old_bytesize, PROT_READ | PROT_WRITE,
71 MAP_PRIVATE | MAP_ANONYMOUS | MAP_POPULATE, -1, 0);
72 xbt_assert(new_memory != MAP_FAILED, "Could not mremap snapshot pages.");
73 // Check if expanding worked
74 if (new_memory == (char*)this->memory_ + old_bytesize) {
75 new_memory = this->memory_;
77 // New memory segment could not be put at the end of this->memory_,
78 // so cancel this one and try to relocate everything and copy data
79 munmap(new_memory, new_bytesize - old_bytesize);
81 mmap(nullptr, new_bytesize, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS | MAP_POPULATE, -1, 0);
82 xbt_assert(new_memory != MAP_FAILED, "Could not mremap snapshot pages.");
83 memcpy(new_memory, this->memory_, old_bytesize);
84 munmap(this->memory_, old_bytesize);
87 // We don't have functions to shrink a mapping, so leave memory as
89 new_memory = this->memory_;
93 this->capacity_ = size;
94 this->memory_ = new_memory;
95 this->page_counts_.resize(size, 0);
98 /** Allocate a free page
100 * @return index of the free page
102 std::size_t PageStore::alloc_page()
104 if (this->free_pages_.empty()) {
105 // Expand the region:
106 if (this->top_index_ == this->capacity_)
107 // All the pages are allocated, we need add more pages:
108 this->resize(2 * this->capacity_);
110 // Use a page from the top:
111 return this->top_index_++;
113 // Use a page from free_pages_ (inside of the region):
114 size_t res = this->free_pages_[this->free_pages_.size() - 1];
115 this->free_pages_.pop_back();
120 void PageStore::remove_page(std::size_t pageno)
122 this->free_pages_.push_back(pageno);
123 const void* page = this->get_page(pageno);
124 hash_type hash = mc_hash_page(page);
125 this->hash_index_[hash].erase(pageno);
128 /** Store a page in memory */
129 std::size_t PageStore::store_page(const void* page)
131 xbt_assert(top_index_ <= this->capacity_, "top_index is not consistent");
133 // First, we check if a page with the same content is already in the page store:
134 // 1. compute the hash of the page
135 // 2. find pages with the same hash using `hash_index_`
136 // 3. find a page with the same content
137 hash_type hash = mc_hash_page(page);
139 // Try to find a duplicate in set of pages with the same hash:
140 page_set_type& page_set = this->hash_index_[hash];
141 for (size_t const& pageno : page_set) {
142 const void* snapshot_page = this->get_page(pageno);
143 if (memcmp(page, snapshot_page, xbt_pagesize) == 0) {
144 // If a page with the same content is already in the page store it's reused and its refcount is incremented.
145 page_counts_[pageno]++;
150 // Otherwise, a new page is allocated in the page store and the content of the page is `memcpy()`-ed to this new page.
151 std::size_t pageno = alloc_page();
152 xbt_assert(this->page_counts_[pageno] == 0, "Allocated page is already used");
153 void* snapshot_page = this->get_page(pageno);
154 memcpy(snapshot_page, page, xbt_pagesize);
155 page_set.insert(pageno);
156 page_counts_[pageno]++;
160 } // namespace simgrid::mc