Add a downstairs memory endpoint for inspection

downstairs-api/src/lib.rs

@@ -23,6 +23,7 @@ api_versions!([
     // |  example for the next person.
     // v
     // (next_int, IDENT),
+    (2, MEMORY),
     (1, INITIAL),
 ]);
 
@@ -122,4 +123,14 @@ pub trait CrucibleDownstairsRepairApi {
     async fn get_work(
         rqctx: RequestContext<Self::Context>,
     ) -> Result<HttpResponseOk<bool>, HttpError>;
+
+    /// Memory usage report
+    #[endpoint {
+        method = GET,
+        path = "/memory",
+        versions = VERSION_MEMORY..,
+    }]
+    async fn get_memory(
+        rqctx: RequestContext<Self::Context>,
+    ) -> Result<HttpResponseOk<latest::repair::MemoryReport>, HttpError>;
 }

downstairs-types/versions/src/initial/repair.rs

@@ -1,7 +1,7 @@
 // Copyright 2026 Oxide Computer Company
 
 use schemars::JsonSchema;
-use serde::Deserialize;
+use serde::{Deserialize, Serialize};
 
 #[derive(Deserialize, JsonSchema)]
 #[serde(rename_all = "camelCase")]
@@ -37,3 +37,40 @@ pub struct ExtentFilePath {
 pub struct JobPath {
     pub id: String,
 }
+
+/// Per-connection memory report
+#[derive(Debug, Clone, Serialize, Deserialize, JsonSchema)]
+pub struct ConnectionMemoryReport {
+    pub pending_jobs: usize,
+    pub pending_jobs_bytes: usize,
+    pub pending_jobs_capacity_hwm: usize,
+    pub completed_ranges: usize,
+    pub completed_ranges_hwm: usize,
+}
+
+/// Summary of downstairs memory usage
+#[derive(Debug, Clone, Serialize, Deserialize, JsonSchema)]
+pub struct MemoryReport {
+    // Region configuration for context
+    pub extent_count: u32,
+    pub extent_size: u64,
+    pub block_size: u64,
+
+    // Region memory
+    pub region_bytes: usize,
+    pub extent_meta_bytes: usize,
+    pub bytes_per_extent: usize,
+    pub dirty_extent_count: usize,
+
+    // High-water marks for transient I/O buffers
+    pub read_bytes_hwm: usize,
+    pub write_bytes_hwm: usize,
+
+    // Thread counts
+    pub tokio_worker_threads: usize,
+    pub rayon_threads: usize,
+
+    // Connection memory
+    pub active_connections: usize,
+    pub connections: Vec<ConnectionMemoryReport>,
+}

downstairs-types/versions/src/latest.rs

@@ -7,9 +7,11 @@ pub mod admin {
 }
 
 pub mod repair {
+    pub use crate::v1::repair::ConnectionMemoryReport;
     pub use crate::v1::repair::ExtentFilePath;
     pub use crate::v1::repair::ExtentPath;
     pub use crate::v1::repair::FileSpec;
     pub use crate::v1::repair::FileType;
     pub use crate::v1::repair::JobPath;
+    pub use crate::v1::repair::MemoryReport;
 }

downstairs/src/complete_jobs.rs

@@ -43,6 +43,11 @@ impl CompletedJobs {
         self.completed.contains(&id)
     }
 
+    /// Returns the number of contiguous ranges stored
+    pub fn range_count(&self) -> usize {
+        self.completed.iter().count()
+    }
+
     /// Returns the list of completed jobs
     pub fn completed(&self) -> impl Iterator<Item = JobId> + use<'_> {
         self.completed

downstairs/src/extent.rs

@@ -115,6 +115,10 @@ pub(crate) trait ExtentInner: Send + Sync + Debug {
         &mut self,
         block_context: &DownstairsBlockContext,
     ) -> Result<(), CrucibleError>;
+
+    /// Returns the heap bytes allocated by this extent's in-memory
+    /// metadata (not the on-disk file data).
+    fn heap_size(&self) -> usize;
 }
 
 /// BlockContext, with the addition of block index and on_disk_hash
@@ -716,6 +720,19 @@ impl Extent {
     ) -> Result<Vec<Option<DownstairsBlockContext>>, CrucibleError> {
         self.inner.get_block_contexts(block, count)
     }
+
+    pub fn heap_size(&self) -> usize {
+        self.inner.heap_size()
+    }
+}
+
+impl ExtentState {
+    pub fn heap_size(&self) -> usize {
+        match self {
+            ExtentState::Opened(extent) => extent.heap_size(),
+            ExtentState::Closed => 0,
+        }
+    }
 }
 
 /**

downstairs/src/extent_inner_raw.rs

@@ -177,6 +177,10 @@ impl BlockBitArray {
         self.block_count as usize
     }
 
+    fn heap_size(&self) -> usize {
+        self.data.capacity() * size_of::<u32>()
+    }
+
     fn iter(&self) -> impl Iterator<Item = bool> + '_ {
         (0..self.block_count).map(|i| self[i])
     }
@@ -687,6 +691,12 @@ impl ExtentInner for RawInner {
     ) -> Result<Vec<Option<DownstairsBlockContext>>, CrucibleError> {
         RawInner::get_block_contexts(self, block, count)
     }
+
+    fn heap_size(&self) -> usize {
+        size_of_val(self)
+            + self.active_context.0.heap_size()
+            + self.block_dirty.heap_size()
+    }
 }
 
 impl RawInner {

downstairs/src/extent_inner_sqlite.rs

@@ -118,6 +118,10 @@ impl ExtentInner for SqliteInner {
             .unwrap()
             .set_dirty_and_block_context(block_context)
     }
+
+    fn heap_size(&self) -> usize {
+        0
+    }
 }
 
 impl SqliteInner {