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page_map.rs
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page_map.rs
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mod checkpoint;
pub mod int_map;
mod page_allocator;
use checkpoint::Checkpoint;
pub use checkpoint::{CheckpointSerialization, MappingSerialization};
use ic_sys::PageBytes;
pub use ic_sys::{PageIndex, PAGE_SIZE};
use ic_utils::deterministic_operations::deterministic_copy_from_slice;
pub use page_allocator::{
allocated_pages_count, PageAllocatorSerialization, PageDeltaSerialization, PageSerialization,
};
// Exported publicly for benchmarking.
pub use page_allocator::{DefaultPageAllocatorImpl, HeapBasedPageAllocator, PageAllocatorInner};
// NOTE: We use a persistent map to make snapshotting of a PageMap a cheap
// operation. This allows us to simplify canister state management: we can
// simply have a copy of the whole PageMap in every canister snapshot.
use ic_types::Height;
use int_map::IntMap;
use libc::off_t;
use page_allocator::{Page, PageAllocator};
use serde::{Deserialize, Serialize};
use std::collections::HashMap;
use std::fs::{File, OpenOptions};
use std::ops::Range;
use std::os::unix::io::RawFd;
use std::path::Path;
/// `PageDelta` represents a changeset of the module heap.
#[derive(Clone, Default, Debug)]
struct PageDelta(IntMap<Page>);
impl PageDelta {
/// Gets content of the page at the specified index.
///
/// The given `page_allocator` must be the same as the one used for
/// allocating pages in this `PageDelta`. It serves as a witness that
/// the contents of the page is still valid.
fn get_page(&self, page_index: PageIndex) -> Option<&PageBytes> {
self.0.get(page_index.get()).map(|p| p.contents())
}
/// Returns a reference to the page at the specified index.
fn get_page_ref(&self, page_index: PageIndex) -> Option<&Page> {
self.0.get(page_index.get())
}
/// Gets an inclusive range of pages that contains the given page.
fn bounds(&self, page_index: PageIndex) -> (Option<PageIndex>, Option<PageIndex>) {
let (lower, upper) = self.0.bounds(page_index.get());
(lower.map(PageIndex::new), upper.map(PageIndex::new))
}
/// Modifies this delta in-place by applying all the entries in `rhs` to it.
fn update(&mut self, rhs: PageDelta) {
self.0 = rhs.0.union(std::mem::take(&mut self.0));
}
/// Enumerates all the pages in this delta.
fn iter(&self) -> impl Iterator<Item = (PageIndex, &'_ Page)> {
self.0.iter().map(|(idx, page)| (PageIndex::new(idx), page))
}
/// Applies this delta to the specified file.
/// Precondition: `file` is seekable and writeable.
fn apply_to_file(&self, file: &mut File, path: &Path) -> Result<(), PersistenceError> {
use std::io::{Seek, SeekFrom};
for (index, page) in self.iter() {
let offset = index.get() * PAGE_SIZE as u64;
file.seek(SeekFrom::Start(offset as u64)).map_err(|err| {
PersistenceError::FileSystemError {
path: path.display().to_string(),
context: format!("Failed to seek to {}", offset),
internal_error: err.to_string(),
}
})?;
let mut contents = page.contents() as &[u8];
std::io::copy(&mut contents, file).map_err(|err| {
PersistenceError::FileSystemError {
path: path.display().to_string(),
context: format!("Failed to copy page #{}", index),
internal_error: err.to_string(),
}
})?;
}
Ok(())
}
/// Persists this delta to the specified destination.
fn persist(&self, dst: &Path) -> Result<(), PersistenceError> {
let mut file = OpenOptions::new()
.write(true)
.create(true)
.open(dst)
.map_err(|err| PersistenceError::FileSystemError {
path: dst.display().to_string(),
context: "Failed to open file".to_string(),
internal_error: err.to_string(),
})?;
self.apply_to_file(&mut file, dst)?;
Ok(())
}
/// Persists this delta to the specified destination and flushes it.
fn persist_and_sync(&self, dst: &Path) -> Result<(), PersistenceError> {
let mut file = OpenOptions::new()
.write(true)
.create(true)
.open(dst)
.map_err(|err| PersistenceError::FileSystemError {
path: dst.display().to_string(),
context: "Failed to open file".to_string(),
internal_error: err.to_string(),
})?;
self.apply_to_file(&mut file, dst)?;
file.sync_all()
.map_err(|err| PersistenceError::FileSystemError {
path: dst.display().to_string(),
context: "Failed to sync file".to_string(),
internal_error: err.to_string(),
})?;
Ok(())
}
/// Returns true if the page delta contains no pages.
fn is_empty(&self) -> bool {
self.0.is_empty()
}
}
impl<I> From<I> for PageDelta
where
I: IntoIterator<Item = (PageIndex, Page)>,
{
fn from(delta: I) -> Self {
Self(delta.into_iter().map(|(i, p)| (i.get(), p)).collect())
}
}
/// Errors that can happen when one saves or loads a PageMap.
#[derive(Clone, Debug, PartialEq, Eq, Hash)]
pub enum PersistenceError {
/// I/O error while interacting with the filesystem.
FileSystemError {
path: String,
context: String,
internal_error: String,
},
/// Error trying to memory map a file.
MmapError {
path: String,
len: usize,
internal_error: String,
},
/// File is not a multiple of the page size.
InvalidHeapFile {
path: String,
file_size: usize,
page_size: usize,
},
/// (Slice) size is not equal to page size.
BadPageSize { expected: usize, actual: usize },
}
impl PersistenceError {
pub fn is_invalid_heap_file(&self) -> bool {
matches!(self, PersistenceError::InvalidHeapFile { .. })
}
}
impl std::error::Error for PersistenceError {
fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
None
}
}
impl std::fmt::Display for PersistenceError {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
match self {
PersistenceError::FileSystemError {
path,
context,
internal_error,
} => {
write!(
f,
"File system error for file {}: {} {}",
path, context, internal_error
)
}
PersistenceError::MmapError { path, len, .. } => {
write!(f, "Failed to memory map file {} of length {}", path, len)
}
PersistenceError::InvalidHeapFile {
path,
file_size,
page_size,
} => write!(
f,
"Size of heap file {} is {}, which is not a multiple of the page size {}",
path, file_size, page_size
),
PersistenceError::BadPageSize { expected, actual } => write!(
f,
"Bad slice size: expected {}, actual {}",
expected, actual
),
}
}
}
/// A wrapper around the raw file descriptor to be used for memory mapping the
/// file into the Wasm heap while executing a canister.
#[derive(Serialize, Deserialize, Clone, Debug)]
pub struct FileDescriptor {
pub fd: RawFd,
}
/// A type alias for a raw offset within a file. It is not wrapped in a struct
/// to simplify arithmetic operations.
pub type FileOffset = off_t;
/// The result of the `get_memory_region(page_index)` function. It specifies the
/// largest contiguous page range that contains the given page such that all
/// pages share the same backing store. There are three possible cases:
/// - The page is not in the current `PageMap` and it is zero initialized.
/// - The page maps to the checkpoint file.
/// - The page is in the page delta of the current `PageMap`. In this case the
/// range is a singleton and its contents need to be copied out.
pub enum MemoryRegion<'a> {
Zeros(Range<PageIndex>),
BackedByFile(Range<PageIndex>, FileDescriptor),
BackedByPage(&'a PageBytes),
}
/// PageMap is a data structure that represents an image of a canister virtual
/// memory. The memory is viewed as a collection of _pages_. `PageMap` uses
/// 4KiB host OS pages to track the heap contents, not 64KiB Wasm pages.
///
/// The map only contains the "modified prefix" of the heap. Modified prefix is
/// the minimal continuous range of the memory pages a canister ever written
/// data to. E.g., if a canister only issued XXX.load instructions to addresses
/// belonging to pages {0, 1, 5, 100}, its modified prefix is the content of
/// pages [0,100], and the length of the modified prefix in pages is 101.
///
/// If a canister Wasm module requested more memory (say, 200 pages) but never
/// accessed it, it won't be explicitly stored in the `PageMap`.
///
/// `PageMap` is designed to be cheap to copy so that heap can be easily
/// versioned.
#[derive(Clone, Default)]
pub struct PageMap {
/// The checkpoint that is used for all the pages that can not be found in
/// the `page_delta`.
checkpoint: Checkpoint,
/// The height of the checkpoint that backs the page map.
pub base_height: Option<Height>,
/// The map containing pages overriding pages from the `checkpoint`.
/// We need these pages to be able to reconstruct the full heap.
/// It is reset when `strip_all_deltas()` method is called.
page_delta: PageDelta,
/// The map containing deltas accumulated since the beginning of the
/// execution round. It is reset when `strip_round_delta()` or
/// `strip_all_deltas()` methods are called.
///
/// Invariant: round_delta ⊆ page_delta
round_delta: PageDelta,
/// The allocator for PageDelta pages.
/// It is reset when `strip_all_deltas()` method is called.
page_allocator: PageAllocator,
}
impl PageMap {
/// Creates a new page map that always returns zeroed pages.
pub fn new() -> Self {
// Ensure that the hardcoded constant matches the OS page size.
assert_eq!(ic_sys::sysconf_page_size(), PAGE_SIZE);
Default::default()
}
/// Creates a page map backed by the provided heap file.
///
/// Note that the file is assumed to be read-only.
pub fn open(heap_file: &Path, base_height: Option<Height>) -> Result<Self, PersistenceError> {
let checkpoint = Checkpoint::open(heap_file)?;
Ok(Self {
checkpoint,
base_height,
page_delta: Default::default(),
round_delta: Default::default(),
page_allocator: Default::default(),
})
}
/// Returns a serialization-friendly representation of the page-map.
pub fn serialize(&self) -> PageMapSerialization {
PageMapSerialization {
checkpoint: self.checkpoint.serialize(),
base_height: self.base_height,
page_delta: self
.page_allocator
.serialize_page_delta(self.page_delta.iter()),
round_delta: self
.page_allocator
.serialize_page_delta(self.round_delta.iter()),
page_allocator: self.page_allocator.serialize(),
}
}
/// Creates a page-map from the given serialization-friendly representation.
pub fn deserialize(page_map: PageMapSerialization) -> Result<Self, PersistenceError> {
let checkpoint = Checkpoint::deserialize(page_map.checkpoint)?;
let page_allocator = PageAllocator::deserialize(page_map.page_allocator);
let page_delta =
PageDelta::from(page_allocator.deserialize_page_delta(page_map.page_delta));
let round_delta =
PageDelta::from(page_allocator.deserialize_page_delta(page_map.round_delta));
Ok(Self {
checkpoint,
base_height: page_map.base_height,
page_delta,
round_delta,
page_allocator,
})
}
/// Returns a serialization-friendly representation of the page allocator.
pub fn serialize_allocator(&self) -> PageAllocatorSerialization {
self.page_allocator.serialize()
}
/// Creates and sets the page allocator from the given
/// serialization-friendly representation.
pub fn deserialize_allocator(&mut self, page_allocator: PageAllocatorSerialization) {
self.page_allocator = PageAllocator::deserialize(page_allocator);
}
/// Returns a serialization-friendly representation of the page delta.
pub fn serialize_delta(&self, pages: &[PageIndex]) -> PageDeltaSerialization {
self.page_allocator.serialize_page_delta(
pages
.iter()
.map(|index| (*index, self.page_delta.get_page_ref(*index).unwrap())),
)
}
/// Creates and applies the page delta from the given serialization-friendly
/// representation.
pub fn deserialize_delta(&mut self, page_delta: PageDeltaSerialization) {
let page_delta = self.page_allocator.deserialize_page_delta(page_delta);
self.apply(page_delta);
}
/// Modifies this page map by adding the given dirty pages to it.
/// Returns a list of dirty page indicies and an indication of whether the
/// page allocator was created or not, which is used for synchronization
/// with the sandbox process.
pub fn update(&mut self, pages: &[(PageIndex, &PageBytes)]) -> Vec<PageIndex> {
let page_delta = self.page_allocator.allocate(pages);
self.apply(page_delta);
pages.iter().map(|(index, _)| *index).collect()
}
/// Persists the heap delta contained in this page map to the specified
/// destination.
pub fn persist_delta(&self, dst: &Path) -> Result<(), PersistenceError> {
self.page_delta.persist(dst)
}
/// Persists the heap delta contained in this page map to the specified
/// destination and fsync the file to disk.
pub fn persist_and_sync_delta(&self, dst: &Path) -> Result<(), PersistenceError> {
self.page_delta.persist_and_sync(dst)
}
/// Persists the round delta contained in this page map to the specified
/// destination.
pub fn persist_round_delta(&self, dst: &Path) -> Result<(), PersistenceError> {
self.round_delta.persist(dst)
}
/// Returns the iterator over host pages managed by this `PageMap`.
pub fn host_pages_iter(&self) -> impl Iterator<Item = (PageIndex, &PageBytes)> + '_ {
(0..self.num_host_pages()).map(move |i| {
let idx = PageIndex::from(i as u64);
(idx, self.get_page(idx))
})
}
/// Returns the page with the specified `page_index`.
pub fn get_page(&self, page_index: PageIndex) -> &PageBytes {
match self.page_delta.get_page(page_index) {
Some(page) => page,
None => self.checkpoint.get_page(page_index),
}
}
/// Returns the largest contiguous range of pages that contains the given
/// page such that all pages share the same backing store.
pub fn get_memory_region(&self, page_index: PageIndex) -> MemoryRegion {
match self.page_delta.get_page(page_index) {
Some(page) => MemoryRegion::BackedByPage(page),
None => {
let (start, end) = self.page_delta.bounds(page_index);
let start = match start {
None => PageIndex::new(0),
Some(start) => {
// Here `start` is a page in `page_delta`. We need to skip that page to
// get to the start of the checkpoint region that contains `page_index`.
PageIndex::new(start.get() + 1)
}
};
let end = match end {
None => PageIndex::new(u64::MAX),
Some(end) => {
// Here `end` is a page in `page_delta`. Since we will use it as the end of
// half-open `Range`, so we can take it as is without decrementing.
end
}
};
let range = Range { start, end };
assert!(range.contains(&page_index));
self.checkpoint.get_memory_region(page_index, range)
}
}
}
/// Returns the whole checkpoint memory region.
pub fn get_checkpoint_memory_region(&self) -> MemoryRegion {
let start = PageIndex::new(0);
let end = PageIndex::new(u64::MAX);
self.checkpoint
.get_memory_region(start, Range { start, end })
}
/// Removes the page delta from this page map.
pub fn strip_all_deltas(&mut self) {
// Ensure that all pages are dropped before we drop the page allocator.
// This is not necessary for correctness in the current implementation,
// because page destructors are currently trivial. Nevertheless, it is
// a good property to maintain.
{
std::mem::take(&mut self.page_delta);
std::mem::take(&mut self.round_delta);
}
std::mem::take(&mut self.page_allocator);
}
/// Removes the round delta from this page map.
pub fn strip_round_delta(&mut self) {
std::mem::take(&mut self.round_delta);
}
pub fn get_page_delta_indices(&self) -> Vec<PageIndex> {
self.page_delta.iter().map(|(index, _)| index).collect()
}
/// Returns the length of the modified prefix in host pages.
///
/// Also, the following property holds:
///
/// ```text
/// ∀ n . n ≥ self.num_host_pages() ⇒ self.get_page(n) = ZERO_PAGE
/// ```
pub fn num_host_pages(&self) -> usize {
let pages_in_checkpoint = self.checkpoint.num_pages();
pages_in_checkpoint.max(
self.page_delta
.iter()
.map(|(k, _v)| (k.get() + 1) as usize)
.max()
.unwrap_or(pages_in_checkpoint),
)
}
/// Switches the checkpoint file of the current page map to the one provided
/// by the given page map. Page deltas of both page maps must be empty.
pub fn switch_to_checkpoint(&mut self, checkpointed_page_map: &PageMap) {
self.checkpoint = checkpointed_page_map.checkpoint.clone();
// Also copy the base height to reflect the height of the new checkpoint.
self.base_height = checkpointed_page_map.base_height;
assert!(self.page_delta.is_empty());
assert!(self.round_delta.is_empty());
assert!(checkpointed_page_map.page_delta.is_empty());
assert!(checkpointed_page_map.round_delta.is_empty());
// Keep the page allocators of the states disjoint.
}
// Modifies this page map by applying the given page delta to it.
fn apply<I>(&mut self, delta: I)
where
I: IntoIterator<Item = (PageIndex, Page)>,
{
let delta = PageDelta::from(delta);
// Delta is a persistent data structure and is cheap to clone.
self.page_delta.update(delta.clone());
self.round_delta.update(delta)
}
}
impl From<&[u8]> for PageMap {
fn from(bytes: &[u8]) -> Self {
let mut buf = Buffer::new(PageMap::default());
buf.write(bytes, 0);
let mut page_map = PageMap::default();
page_map.update(&buf.dirty_pages().collect::<Vec<_>>());
page_map
}
}
/// Buffer provides a file-like interface to a PageMap.
pub struct Buffer {
page_map: PageMap,
/// The map containing pages modified by the caller since this buffer was
/// created. These pages can be modified in-place by the write method.
///
/// Note: using a hash map here is beneficial for performance and doesn't
/// affect determinism because the state machine has no way of observing the
/// order of the keys in this map (or even inside of PageDelta for that
/// matter).
dirty_pages: HashMap<PageIndex, PageBytes>,
}
impl Buffer {
/// Constructs a new buffer backed by the specified page map.
pub fn new(page_map: PageMap) -> Self {
Self {
page_map,
dirty_pages: HashMap::new(),
}
}
/// Reads the contents of this buffer at the specified offset into the
/// specified destination buffer.
pub fn read(&self, mut dst: &mut [u8], mut offset: usize) {
let page_size = PAGE_SIZE;
while !dst.is_empty() {
let page = PageIndex::new((offset / page_size) as u64);
let offset_into_page = offset % page_size;
let page_len = dst.len().min(page_size - offset_into_page);
let page_contents = match self.dirty_pages.get(&page) {
Some(bytes) => bytes,
None => self.page_map.get_page(page),
};
deterministic_copy_from_slice(
&mut dst[0..page_len],
&page_contents[offset_into_page..offset_into_page + page_len],
);
offset += page_len;
let n = dst.len();
dst = &mut dst[page_len..n];
}
}
/// Overwrites the contents of this buffer at the specified offset with the
/// contents of the source buffer.
pub fn write(&mut self, mut src: &[u8], mut offset: usize) {
let page_size = PAGE_SIZE;
while !src.is_empty() {
let page = PageIndex::new((offset / page_size) as u64);
let offset_into_page = offset % page_size;
let page_len = src.len().min(page_size - offset_into_page);
let dirty_page = self
.dirty_pages
.entry(page)
.or_insert(*self.page_map.get_page(page));
deterministic_copy_from_slice(
&mut dirty_page[offset_into_page..offset_into_page + page_len],
&src[0..page_len],
);
offset += page_len;
src = &src[page_len..src.len()];
}
}
pub fn dirty_pages(&self) -> impl Iterator<Item = (PageIndex, &PageBytes)> {
self.dirty_pages.iter().map(|(i, p)| (*i, p))
}
pub fn into_page_map(&self) -> PageMap {
let mut page_map = self.page_map.clone();
page_map.update(&self.dirty_pages().collect::<Vec<_>>());
page_map
}
}
// We have to implement the equality by hand because the derived one
// is not correct: two page maps can be equal even if their
// checkpoints and deltas not equal. Example:
//
// `(C={(0, X), (1, Y)}, Δ={(1, Z)}) = (C={(0, X), (1, Z)}, Δ=∅)`
//
// So we compare the total number of pages and equality of each page
// instead.
impl PartialEq for PageMap {
fn eq(&self, rhs: &PageMap) -> bool {
if self.num_host_pages() != rhs.num_host_pages() {
return false;
}
self.host_pages_iter().eq(rhs.host_pages_iter())
}
}
impl Eq for PageMap {}
impl std::fmt::Debug for PageMap {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
let n = self.num_host_pages();
write!(f, "{{")?;
(0..n)
.map(|i| {
let idx = PageIndex::from(i as u64);
ic_utils::rle::display(self.get_page(idx))
})
.try_for_each(|s| write!(f, "[{:?}]", s))?;
write!(f, "}}")
}
}
/// Serialization-friendly representation of `PageMap`.
///
/// It contains sufficient information to reconstruct `PageMap`
/// in another process. Note that canister sandboxing does not
/// need `round_delta`, but the field is kept for consistency here.
#[derive(Serialize, Deserialize, Clone, Debug)]
pub struct PageMapSerialization {
pub checkpoint: CheckpointSerialization,
pub base_height: Option<Height>,
pub page_delta: PageDeltaSerialization,
pub round_delta: PageDeltaSerialization,
pub page_allocator: PageAllocatorSerialization,
}
#[cfg(test)]
mod tests;