Remove redundant memory reserve

When canister memory still was small (and unmanaged) it was sensible
to reserve some space at the end. Now that the canister could in
theory address over 400GB of space _and_ we have more convenient ways
to access that than write into the end adresses, that complexity can
be removed.

The WASM page size constant is also redundant, as it is now provided
by the CDK.

src/internet_identity/src/storage.rs

@@ -63,6 +63,7 @@
 //! The [PersistentState] is serialized at the end of stable memory to allow for variable sized data
 //! without the risk of running out of space (which might easily happen if the RESERVED_HEADER_BYTES
 //! were used instead).
+use ic_cdk::api::stable::WASM_PAGE_SIZE_IN_BYTES;
 use std::borrow::Cow;
 use std::fmt;
 use std::io::{Read, Write};
@@ -94,22 +95,18 @@ mod tests;
 // version  8+: invalid
 const SUPPORTED_LAYOUT_VERSIONS: RangeInclusive<u8> = 7..=7;
 
-const WASM_PAGE_SIZE: u64 = 65_536;
-
 /// Reserved space for the header before the anchor records start.
-const ENTRY_OFFSET: u64 = 2 * WASM_PAGE_SIZE; // 1 page reserved for II config, 1 for memory manager
+const ENTRY_OFFSET: u64 = 2 * WASM_PAGE_SIZE_IN_BYTES as u64; // 1 page reserved for II config, 1 for memory manager
 const DEFAULT_ENTRY_SIZE: u16 = 4096;
 const EMPTY_SALT: [u8; 32] = [0; 32];
 const GB: u64 = 1 << 30;
 
 const MAX_STABLE_MEMORY_SIZE: u64 = 32 * GB;
-const MAX_WASM_PAGES: u64 = MAX_STABLE_MEMORY_SIZE / WASM_PAGE_SIZE;
+const MAX_WASM_PAGES: u64 = MAX_STABLE_MEMORY_SIZE / WASM_PAGE_SIZE_IN_BYTES as u64;
 
 /// In practice, II has 48 GB of stable memory available.
 /// This limit has last been raised when it was still 32 GB.
 const STABLE_MEMORY_SIZE: u64 = 32 * GB;
-/// We reserve the last ~800 MB of stable memory for later new features.
-const STABLE_MEMORY_RESERVE: u64 = 8 * GB / 10;
 
 const PERSISTENT_STATE_MAGIC: [u8; 4] = *b"IIPS"; // II Persistent State
 
@@ -123,8 +120,7 @@ const ANCHOR_MEMORY_ID: MemoryId = MemoryId::new(ANCHOR_MEMORY_INDEX);
 const BUCKET_SIZE_IN_PAGES: u16 = 128;
 
 /// The maximum number of anchors this canister can store.
-pub const DEFAULT_RANGE_SIZE: u64 =
-    (STABLE_MEMORY_SIZE - ENTRY_OFFSET - STABLE_MEMORY_RESERVE) / DEFAULT_ENTRY_SIZE as u64;
+pub const DEFAULT_RANGE_SIZE: u64 = (STABLE_MEMORY_SIZE - ENTRY_OFFSET) / DEFAULT_ENTRY_SIZE as u64;
 
 pub type Salt = [u8; 32];
 
@@ -334,8 +330,8 @@ impl<M: Memory + Clone> Storage<M> {
 
     /// Returns the maximum number of entries that this storage can fit.
     pub fn max_entries(&self) -> usize {
-        ((STABLE_MEMORY_SIZE - self.header.first_entry_offset - STABLE_MEMORY_RESERVE)
-            / self.header.entry_size as u64) as usize
+        ((STABLE_MEMORY_SIZE - self.header.first_entry_offset) / self.header.entry_size as u64)
+            as usize
     }
 
     pub fn assigned_anchor_number_range(&self) -> (AnchorNumber, AnchorNumber) {

src/internet_identity/tests/integration/http.rs

@@ -178,7 +178,7 @@ fn metrics_should_list_expected_user_range() -> Result<(), CallError> {
     let (min_user_number, _) = parse_metric(&metrics, "internet_identity_min_user_number");
     let (max_user_number, _) = parse_metric(&metrics, "internet_identity_max_user_number");
     assert_eq!(min_user_number, 10_000f64);
-    assert_eq!(max_user_number, 8_188_859f64);
+    assert_eq!(max_user_number, 8_398_575f64);
     Ok(())
 }