keep the HardwareManager handle around instead of caching measurements

the number of physical pages won't change at runtime really, nor will
the size of pages, but it seems a bit nicer this way..

Author: iximeow

sled-hardware/src/lib.rs

@@ -77,12 +77,9 @@ pub enum SledMode {
 }
 
 /// Accounting for high watermark memory usage for various system purposes
-#[derive(Copy, Clone, Debug)]
+#[derive(Clone)]
 pub struct MemoryReservations {
-    /// Installed physical memory in this sled. Probably should hold a
-    /// [`HardwareManager`] and call `usable_physical_ram_bytes()` instead of
-    /// this.
-    hardware_physical_ram_bytes: u64,
+    hardware_manager: HardwareManager,
     /// The amount of memory expected to be used if "control plane" services all
     /// running on this sled. "control plane" here refers to services that have
     /// roughly fixed memory use given differing sled hardware configurations.
@@ -98,10 +95,6 @@ pub struct MemoryReservations {
     // XXX: This is really something we should be told by Neuxs, perhaps after
     // starting with this conservative estimate to get the sled started.
     control_plane_earmark_bytes: u64,
-    /// The amount of memory used for `page_t` structures, assuming a distinct
-    /// `page_t` for each 4k page in the system. If we use larger pages, like
-    /// 2MiB pages, this will be potentially a gross overestimate.
-    max_page_t_space: u64,
     // XXX: Crucible involves some amount of memory in support of the volumes it
     // manages. We should collect zpool size and estimate the memory that would
     // be used if all available storage was dedicated to Crucible volumes. For
@@ -113,23 +106,12 @@ impl MemoryReservations {
         hardware_manager: HardwareManager,
         control_plane_earmark_mib: Option<u32>,
     ) -> MemoryReservations {
-        let hardware_physical_ram_bytes =
-            hardware_manager.usable_physical_ram_bytes();
-        // Don't like hardcoding a struct size from the host OS here like
-        // this, maybe we shuffle some bits around before merging.. On the
-        // other hand, the last time page_t changed was illumos-gate commit
-        // a5652762e5 from 2006.
-        const PAGE_T_SIZE: u64 = 120;
-        let max_page_t_space =
-            hardware_manager.usable_physical_pages() * PAGE_T_SIZE;
-
         const MIB: u64 = 1024 * 1024;
         let control_plane_earmark_bytes =
             u64::from(control_plane_earmark_mib.unwrap_or(0)) * MIB;
 
         Self {
-            hardware_physical_ram_bytes,
-            max_page_t_space,
+            hardware_manager,
             control_plane_earmark_bytes,
         }
     }
@@ -141,8 +123,18 @@ impl MemoryReservations {
     /// a fixed amount of memory specified by `ReservoirMode::Size` or
     /// a percentage of this amount specified by `ReservoirMode::Percentage`.
     pub fn vmm_eligible(&self) -> u64 {
-        self.hardware_physical_ram_bytes
-            - self.max_page_t_space
+        let hardware_physical_ram_bytes =
+            self.hardware_manager.usable_physical_ram_bytes();
+        // Don't like hardcoding a struct size from the host OS here like
+        // this, maybe we shuffle some bits around before merging.. On the
+        // other hand, the last time page_t changed was illumos-gate commit
+        // a5652762e5 from 2006.
+        const PAGE_T_SIZE: u64 = 120;
+        let max_page_t_space =
+            self.hardware_manager.usable_physical_pages() * PAGE_T_SIZE;
+
+        hardware_physical_ram_bytes
+            - max_page_t_space
             - self.control_plane_earmark_bytes
     }
 }