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 segment could not be put at the end of this->memory_,
76 // so cancel this one and try to relocate everything and copy data
77 munmap(new_memory, new_bytesize - old_bytesize);
79 mmap(nullptr, new_bytesize, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS | MAP_POPULATE, -1, 0);
80 xbt_assert(new_memory != MAP_FAILED, "Could not mremap snapshot pages.");
81 memcpy(new_memory, this->memory_, old_bytesize);
82 munmap(this->memory_, old_bytesize);
85 // We don't have functions to shrink a mapping, so leave memory as
87 new_memory = this->memory_;
91 this->capacity_ = size;
92 this->memory_ = new_memory;
93 this->page_counts_.resize(size, 0);
96 /** Allocate a free page
98 * @return index of the free page
100 std::size_t PageStore::alloc_page()
102 if (this->free_pages_.empty()) {
103 // Expand the region:
104 if (this->top_index_ == this->capacity_)
105 // All the pages are allocated, we need add more pages:
106 this->resize(2 * this->capacity_);
108 // Use a page from the top:
109 return this->top_index_++;
111 // Use a page from free_pages_ (inside of the region):
112 size_t res = this->free_pages_[this->free_pages_.size() - 1];
113 this->free_pages_.pop_back();
118 void PageStore::remove_page(std::size_t pageno)
120 this->free_pages_.push_back(pageno);
121 const void* page = this->get_page(pageno);
122 hash_type hash = mc_hash_page(page);
123 this->hash_index_[hash].erase(pageno);
126 /** Store a page in memory */
127 std::size_t PageStore::store_page(const void* page)
129 xbt_assert(top_index_ <= this->capacity_, "top_index is not consistent");
131 // First, we check if a page with the same content is already in the page store:
132 // 1. compute the hash of the page
133 // 2. find pages with the same hash using `hash_index_`
134 // 3. find a page with the same content
135 hash_type hash = mc_hash_page(page);
137 // Try to find a duplicate in set of pages with the same hash:
138 page_set_type& page_set = this->hash_index_[hash];
139 for (size_t const& pageno : page_set) {
140 const void* snapshot_page = this->get_page(pageno);
141 if (memcmp(page, snapshot_page, xbt_pagesize) == 0) {
142 // If a page with the same content is already in the page store it's reused and its refcount is incremented.
143 page_counts_[pageno]++;
148 // Otherwise, a new page is allocated in the page store and the content of the page is `memcpy()`-ed to this new page.
149 std::size_t pageno = alloc_page();
150 xbt_assert(this->page_counts_[pageno] == 0, "Allocated page is already used");
151 void* snapshot_page = this->get_page(pageno);
152 memcpy(snapshot_page, page, xbt_pagesize);
153 page_set.insert(pageno);
154 page_counts_[pageno]++;
158 } // namespace simgrid::mc