page_api: remove smallvec (#12095)

## Problem

The gRPC `page_api` domain types used smallvecs to avoid heap
allocations in the common case where a single page is requested.

However, this is pointless: the Protobuf types use a normal vec, and
converting a smallvec into a vec always causes a heap allocation anyway.

## Summary of changes

Use a normal `Vec` instead of a `SmallVec` in `page_api` domain types.

Cargo.lock

@@ -4469,7 +4469,6 @@ dependencies = [
  "pageserver_api",
  "postgres_ffi",
  "prost 0.13.5",
- "smallvec",
  "thiserror 1.0.69",
  "tonic 0.13.1",
  "tonic-build",

pageserver/page_api/Cargo.toml

@@ -9,7 +9,6 @@ bytes.workspace = true
 pageserver_api.workspace = true
 postgres_ffi.workspace = true
 prost.workspace = true
-smallvec.workspace = true
 thiserror.workspace = true
 tonic.workspace = true
 utils.workspace = true

pageserver/page_api/src/model.rs

@@ -14,7 +14,6 @@ use std::fmt::Display;
 
 use bytes::Bytes;
 use postgres_ffi::Oid;
-use smallvec::SmallVec;
 // TODO: split out Lsn, RelTag, SlruKind, Oid and other basic types to a separate crate, to avoid
 // pulling in all of their other crate dependencies when building the client.
 use utils::lsn::Lsn;
@@ -302,7 +301,7 @@ pub struct GetPageRequest {
     /// Multiple pages will be executed as a single batch by the Pageserver, amortizing layer access
     /// costs and parallelizing them. This may increase the latency of any individual request, but
     /// improves the overall latency and throughput of the batch as a whole.
-    pub block_numbers: SmallVec<[u32; 1]>,
+    pub block_numbers: Vec<u32>,
 }
 
 impl TryFrom<proto::GetPageRequest> for GetPageRequest {
@@ -320,7 +319,7 @@ impl TryFrom<proto::GetPageRequest> for GetPageRequest {
                 .ok_or(ProtocolError::Missing("read_lsn"))?
                 .try_into()?,
             rel: pb.rel.ok_or(ProtocolError::Missing("rel"))?.try_into()?,
-            block_numbers: pb.block_number.into(),
+            block_numbers: pb.block_number,
         })
     }
 }
@@ -337,7 +336,7 @@ impl TryFrom<GetPageRequest> for proto::GetPageRequest {
             request_class: request.request_class.into(),
             read_lsn: Some(request.read_lsn.try_into()?),
             rel: Some(request.rel.into()),
-            block_number: request.block_numbers.into_vec(),
+            block_number: request.block_numbers,
         })
     }
 }
@@ -410,7 +409,7 @@ pub struct GetPageResponse {
     /// A string describing the status, if any.
     pub reason: Option<String>,
     /// The 8KB page images, in the same order as the request. Empty if status != OK.
-    pub page_images: SmallVec<[Bytes; 1]>,
+    pub page_images: Vec<Bytes>,
 }
 
 impl From<proto::GetPageResponse> for GetPageResponse {
@@ -419,7 +418,7 @@ impl From<proto::GetPageResponse> for GetPageResponse {
             request_id: pb.request_id,
             status_code: pb.status_code.into(),
             reason: Some(pb.reason).filter(|r| !r.is_empty()),
-            page_images: pb.page_image.into(),
+            page_images: pb.page_image,
         }
     }
 }
@@ -430,7 +429,7 @@ impl From<GetPageResponse> for proto::GetPageResponse {
             request_id: response.request_id,
             status_code: response.status_code.into(),
             reason: response.reason.unwrap_or_default(),
-            page_image: response.page_images.into_vec(),
+            page_image: response.page_images,
         }
     }
 }

pageserver/src/page_service.rs

@@ -765,7 +765,7 @@ impl PageStreamError {
             request_id,
             status_code,
             reason: Some(status.message().to_string()),
-            page_images: SmallVec::new(),
+            page_images: Vec::new(),
         }
         .into())
     }
@@ -3521,7 +3521,7 @@ impl GrpcPageServiceHandler {
             request_id: req.request_id,
             status_code: page_api::GetPageStatusCode::Ok,
             reason: None,
-            page_images: SmallVec::with_capacity(results.len()),
+            page_images: Vec::with_capacity(results.len()),
         };
 
         for result in results {