WIP: benchmark that does random getpage requests against the keyspace

backup of pageserver.toml

    d =1
    pg_distrib_dir ='/home/admin/neon-main/pg_install'
    http_auth_type ='Trust'
    pg_auth_type ='Trust'
    listen_http_addr ='127.0.0.1:9898'
    listen_pg_addr ='127.0.0.1:64000'
    broker_endpoint ='http://127.0.0.1:50051/'
    #control_plane_api ='http://127.0.0.1:1234/'

    # Initial configuration file created by 'pageserver --init'
    #listen_pg_addr = '127.0.0.1:64000'
    #listen_http_addr = '127.0.0.1:9898'

    #wait_lsn_timeout = '60 s'
    #wal_redo_timeout = '60 s'

    #max_file_descriptors = 10000
    #page_cache_size = 160000

    # initial superuser role name to use when creating a new tenant
    #initial_superuser_name = 'cloud_admin'

    #broker_endpoint = 'http://127.0.0.1:50051'

    #log_format = 'plain'

    #concurrent_tenant_size_logical_size_queries = '1'

    #metric_collection_interval = '10 min'
    #cached_metric_collection_interval = '0s'
    #synthetic_size_calculation_interval = '10 min'

    #disk_usage_based_eviction = { max_usage_pct = .., min_avail_bytes = .., period = "10s"}

    #background_task_maximum_delay = '10s'

    [tenant_config]
    #checkpoint_distance = 268435456 # in bytes
    #checkpoint_timeout = 10 m
    #compaction_target_size = 134217728 # in bytes
    #compaction_period = '20 s'
    #compaction_threshold = 10

    #gc_period = '1 hr'
    #gc_horizon = 67108864
    #image_creation_threshold = 3
    #pitr_interval = '7 days'

    #min_resident_size_override = .. # in bytes
    #evictions_low_residence_duration_metric_threshold = '24 hour'
    #gc_feedback = false

    # make it determinsitic
    gc_period = '0s'
    checkpoint_timeout = '3650 day'
    compaction_period = '20 s'
    compaction_threshold = 10
    compaction_target_size = 134217728
    checkpoint_distance = 268435456
    image_creation_threshold = 3

    [remote_storage]
    local_path = '/home/admin/neon-main/bench_repo_dir/repo/remote_storage_local_fs'

Cargo.lock

@@ -2568,6 +2568,26 @@ dependencies = [
  "windows-sys 0.48.0",
 ]
 
+[[package]]
+name = "io-uring"
+version = "0.5.13"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dd1e1a01cfb924fd8c5c43b6827965db394f5a3a16c599ce03452266e1cf984c"
+dependencies = [
+ "bitflags",
+ "libc",
+]
+
+[[package]]
+name = "io-uring"
+version = "0.6.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "460648e47a07a43110fbfa2e0b14afb2be920093c31e5dccc50e49568e099762"
+dependencies = [
+ "bitflags",
+ "libc",
+]
+
 [[package]]
 name = "ipnet"
 version = "2.7.2"
@@ -2676,9 +2696,9 @@ checksum = "830d08ce1d1d941e6b30645f1a0eb5643013d835ce3779a5fc208261dbe10f55"
 
 [[package]]
 name = "libc"
-version = "0.2.144"
+version = "0.2.147"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "2b00cc1c228a6782d0f076e7b232802e0c5689d41bb5df366f2a6b6621cfdfe1"
+checksum = "b4668fb0ea861c1df094127ac5f1da3409a82116a4ba74fca2e58ef927159bb3"
 
 [[package]]
 name = "libloading"
@@ -3281,6 +3301,7 @@ dependencies = [
  "tenant_size_model",
  "thiserror",
  "tokio",
+ "tokio-epoll-uring",
  "tokio-io-timeout",
  "tokio-postgres",
  "tokio-tar",
@@ -4524,6 +4545,12 @@ dependencies = [
  "windows-sys 0.42.0",
 ]
 
+[[package]]
+name = "scoped-tls"
+version = "1.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e1cf6437eb19a8f4a6cc0f7dca544973b0b78843adbfeb3683d1a94a0024a294"
+
 [[package]]
 name = "scopeguard"
 version = "1.1.0"
@@ -5220,18 +5247,18 @@ dependencies = [
 
 [[package]]
 name = "thiserror"
-version = "1.0.40"
+version = "1.0.47"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "978c9a314bd8dc99be594bc3c175faaa9794be04a5a5e153caba6915336cebac"
+checksum = "97a802ec30afc17eee47b2855fc72e0c4cd62be9b4efe6591edde0ec5bd68d8f"
 dependencies = [
  "thiserror-impl",
 ]
 
 [[package]]
 name = "thiserror-impl"
-version = "1.0.40"
+version = "1.0.47"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f9456a42c5b0d803c8cd86e73dd7cc9edd429499f37a3550d286d5e86720569f"
+checksum = "6bb623b56e39ab7dcd4b1b98bb6c8f8d907ed255b18de254088016b27a8ee19b"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -5357,22 +5384,39 @@ dependencies = [
 
 [[package]]
 name = "tokio"
-version = "1.28.1"
+version = "1.32.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "0aa32867d44e6f2ce3385e89dceb990188b8bb0fb25b0cf576647a6f98ac5105"
+checksum = "17ed6077ed6cd6c74735e21f37eb16dc3935f96878b1fe961074089cc80893f9"
 dependencies = [
- "autocfg",
+ "backtrace",
  "bytes",
  "libc",
  "mio",
  "num_cpus",
+ "parking_lot 0.12.1",
  "pin-project-lite",
  "signal-hook-registry",
- "socket2 0.4.9",
+ "socket2 0.5.3",
  "tokio-macros",
  "windows-sys 0.48.0",
 ]
 
+[[package]]
+name = "tokio-epoll-uring"
+version = "0.1.0"
+dependencies = [
+ "futures",
+ "io-uring 0.6.2",
+ "libc",
+ "once_cell",
+ "scopeguard",
+ "thiserror",
+ "tokio",
+ "tokio-uring",
+ "tokio-util",
+ "tracing",
+]
+
 [[package]]
 name = "tokio-io-timeout"
 version = "1.2.0"
@@ -5489,6 +5533,20 @@ dependencies = [
  "tungstenite",
 ]
 
+[[package]]
+name = "tokio-uring"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0d5e02bb137e030b3a547c65a3bd2f1836d66a97369fdcc69034002b10e155ef"
+dependencies = [
+ "io-uring 0.5.13",
+ "libc",
+ "scoped-tls",
+ "slab",
+ "socket2 0.4.9",
+ "tokio",
+]
+
 [[package]]
 name = "tokio-util"
 version = "0.7.8"

libs/remote_storage/src/lib.rs

@@ -112,7 +112,7 @@ impl RemotePath {
         self.0.file_name()
     }
 
-    pub fn join(&self, segment: &Utf8Path) -> Self {
+    pub fn join<P: AsRef<Utf8Path>>(&self, segment: P) -> Self {
         Self(self.0.join(segment))
     }
 

pageserver/Cargo.toml

@@ -82,6 +82,8 @@ enum-map.workspace = true
 enumset.workspace = true
 strum.workspace = true
 strum_macros.workspace = true
+tokio-epoll-uring = { path = "/home/admin/tokio-epoll-uring/tokio-epoll-uring" }
+#tokio-epoll-uring = { git = "https://github.com/neondatabase/tokio-epoll-uring.git" , branch = "problame/hacky-openat" }
 
 [dev-dependencies]
 criterion.workspace = true

pageserver/src/bin/getpage_bench.rs

@@ -0,0 +1,208 @@
+use clap::Parser;
+use std::future::Future;
+use hyper::client::conn::Parts;
+use hyper::client::HttpConnector;
+use hyper::{Body, Client, Uri};
+use pageserver::{repository, tenant};
+use rand::prelude::*;
+use std::env::args;
+use std::str::FromStr;
+use std::sync::{Arc, Mutex};
+use std::thread;
+use tokio::sync::mpsc::{channel, Sender};
+use tokio::sync::Mutex as AsyncMutex;
+use tokio::task::JoinHandle;
+
+struct Key(repository::Key);
+
+impl std::str::FromStr for Key {
+    type Err = anyhow::Error;
+
+    fn from_str(s: &str) -> std::result::Result<Self, Self::Err> {
+        repository::Key::from_hex(s).map(Key)
+    }
+}
+
+struct KeyRange {
+    start: Key,
+    end: Key,
+}
+
+impl KeyRange {
+    fn len(&self) -> i128 {
+        self.end.0.to_i128() - self.start.0.to_i128()
+    }
+}
+
+#[derive(clap::Parser)]
+struct Args {
+    #[clap(long, default_value = "http://localhost:9898")]
+    ps_endpoint: String,
+    // tenant_id: String,
+    // timeline_id: String,
+    num_tasks: usize,
+    num_requests: usize,
+    tenants: Option<Vec<String>>,
+    #[clap(long)]
+    pick_n_tenants: Option<usize>,
+}
+
+#[tokio::main]
+async fn main() {
+    let args: &'static Args = Box::leak(Box::new(Args::parse()));
+
+    let client = Client::new();
+
+    let tenants = if let Some(tenants) = &args.tenants {
+        tenants.clone()
+    } else {
+        // let tenant_id = "b97965931096047b2d54958756baee7b";
+        // let timeline_id = "2868f84a8d166779e4c651b116c45059";
+
+        let resp = client
+            .get(Uri::try_from(&format!("{}/v1/tenant", args.ps_endpoint)).unwrap())
+            .await
+            .unwrap();
+
+        let body = hyper::body::to_bytes(resp).await.unwrap();
+        let tenants: serde_json::Value = serde_json::from_slice(&body).unwrap();
+        let mut out = Vec::new();
+        for t in tenants.as_array().unwrap() {
+            if let Some(limit) = args.pick_n_tenants {
+                if out.len() >= limit {
+                    break;
+                }
+            }
+            out.push(t.get("id").unwrap().as_str().unwrap().to_owned());
+        }
+        if let Some(limit) = args.pick_n_tenants {
+            assert_eq!(out.len(), limit);
+        }
+        out
+    };
+
+    let mut tenant_timelines = Vec::new();
+    for tenant_id in tenants {
+        let resp = client
+            .get(
+                Uri::try_from(&format!("{}/v1/tenant/{}/timeline", args.ps_endpoint, tenant_id))
+                    .unwrap(),
+            )
+            .await
+            .unwrap();
+
+        let body = hyper::body::to_bytes(resp).await.unwrap();
+        let timelines: serde_json::Value = serde_json::from_slice(&body).unwrap();
+        for t in timelines.as_array().unwrap() {
+            let timeline_id = t.get("timeline_id").unwrap().as_str().unwrap().to_owned();
+            tenant_timelines.push((tenant_id.clone(), timeline_id));
+        }
+    }
+    println!("tenant_timelines:\n{:?}", tenant_timelines);
+
+    let mut tasks = Vec::new();
+    for (tenant_id, timeline_id) in tenant_timelines {
+        let t = tokio::spawn(timeline(
+            args,
+            client.clone(),
+            tenant_id,
+            timeline_id,
+        ));
+        tasks.push(t);
+    }
+
+    for t in tasks {
+        t.await.unwrap();
+    }
+}
+
+fn timeline(
+    args: &'static Args,
+    client: Client<HttpConnector, Body>,
+    tenant_id: String,
+    timeline_id: String,
+) -> impl Future<Output = ()> {
+    async move {
+        let mut resp = client
+            .get(
+                Uri::try_from(&format!(
+                    "{}/v1/tenant/{}/timeline/{}/keyspace",
+                    args.ps_endpoint, tenant_id, timeline_id
+                ))
+                .unwrap(),
+            )
+            .await
+            .unwrap();
+        if !resp.status().is_success() {
+            panic!("Failed to get keyspace: {resp:?}");
+        }
+        let body = hyper::body::to_bytes(resp).await.unwrap();
+        let keyspace: serde_json::Value = serde_json::from_slice(&body).unwrap();
+
+        let lsn = Arc::new(keyspace["at_lsn"].as_str().unwrap().to_owned());
+
+        let ranges = keyspace["keys"]
+            .as_array()
+            .unwrap()
+            .iter()
+            .map(|r| {
+                let r = r.as_array().unwrap();
+                assert_eq!(r.len(), 2);
+                let start = Key::from_str(r[0].as_str().unwrap()).unwrap();
+                let end = Key::from_str(r[1].as_str().unwrap()).unwrap();
+                KeyRange { start, end }
+            })
+            .collect::<Vec<_>>();
+
+        // weighted ranges
+        let weights = ranges.iter().map(|r| r.len()).collect::<Vec<_>>();
+
+        let ranges = Arc::new(ranges);
+        let weights = Arc::new(weights);
+
+        let (tx, mut rx) = channel::<i32>(1000);
+        let tx = Arc::new(AsyncMutex::new(tx));
+
+        let mut tasks = Vec::<JoinHandle<()>>::new();
+
+        let start = std::time::Instant::now();
+
+        for i in 0..args.num_tasks {
+            let ranges = ranges.clone();
+            let weights = weights.clone();
+            let lsn = lsn.clone();
+            let client = client.clone();
+            let tenant_id = tenant_id.clone();
+            let timeline_id = timeline_id.clone();
+            let task = tokio::spawn(async move {
+                for i in 0..args.num_requests {
+                    let key = {
+                        let mut rng = rand::thread_rng();
+                        let r = ranges.choose_weighted(&mut rng, |r| r.len()).unwrap();
+                        let key = rng.gen_range((r.start.0.to_i128()..r.end.0.to_i128()));
+                        key
+                    };
+                    let url = format!(
+                        "{}/v1/tenant/{}/timeline/{}/getpage?key={:036x}&lsn={}",
+                        args.ps_endpoint, tenant_id, timeline_id, key, lsn
+                    );
+                    let uri = url.parse::<Uri>().unwrap();
+                    let resp = client.get(uri).await.unwrap();
+                }
+            });
+            tasks.push(task);
+        }
+
+        drop(tx);
+
+        for task in tasks {
+            task.await.unwrap();
+        }
+
+        let elapsed = start.elapsed();
+        println!(
+            "RPS: {:.0}",
+            (args.num_requests * args.num_tasks) as f64 / elapsed.as_secs_f64()
+        );
+    }
+}

pageserver/src/http/routes.rs

@@ -681,6 +681,45 @@ async fn tenant_ignore_handler(
     json_response(StatusCode::OK, ())
 }
 
+async fn tenant_duplicate_handler(
+    mut request: Request<Body>,
+    _cancel: CancellationToken,
+) -> Result<Response<Body>, ApiError> {
+    let src_tenant_id: TenantId = parse_request_param(&request, "tenant_id")?;
+
+    let request_data: TenantCreateRequest = json_request(&mut request).await?;
+    let new_tenant_id = request_data.new_tenant_id;
+    check_permission(&request, None)?;
+
+    let _timer = STORAGE_TIME_GLOBAL
+        .get_metric_with_label_values(&[StorageTimeOperation::DuplicateTenant.into()])
+        .expect("bug")
+        .start_timer();
+
+    let tenant_conf =
+        TenantConfOpt::try_from(&request_data.config).map_err(ApiError::BadRequest)?;
+
+    let state = get_state(&request);
+
+    let generation = get_request_generation(state, request_data.generation)?;
+
+    let ctx = RequestContext::new(TaskKind::MgmtRequest, DownloadBehavior::Warn);
+
+    mgr::duplicate_tenant(
+        state.conf,
+        tenant_conf,
+        src_tenant_id,
+        new_tenant_id,
+        generation,
+        state.tenant_resources(),
+        &ctx,
+    )
+    .instrument(info_span!("tenant_duplicate", %src_tenant_id, tenant_id = %new_tenant_id))
+    .await?;
+
+    json_response(StatusCode::CREATED, TenantCreateResponse(new_tenant_id))
+}
+
 async fn tenant_list_handler(
     request: Request<Body>,
     _cancel: CancellationToken,
@@ -1728,6 +1767,9 @@ pub fn make_router(
         .post("/v1/tenant/:tenant_id/ignore", |r| {
             api_handler(r, tenant_ignore_handler)
         })
+        .post("/v1/tenant/:tenant_id/duplicate", |r| {
+            api_handler(r, tenant_duplicate_handler)
+        })
         .get("/v1/tenant/:tenant_id/timeline/:timeline_id", |r| {
             api_handler(r, timeline_detail_handler)
         })

pageserver/src/metrics.rs

@@ -51,6 +51,9 @@ pub enum StorageTimeOperation {
 
     #[strum(serialize = "create tenant")]
     CreateTenant,
+
+    #[strum(serialize = "duplicate tenant")]
+    DuplicateTenant,
 }
 
 pub static STORAGE_TIME_SUM_PER_TIMELINE: Lazy<CounterVec> = Lazy::new(|| {

pageserver/src/tenant/block_io.rs

@@ -5,7 +5,7 @@
 use super::ephemeral_file::EphemeralFile;
 use super::storage_layer::delta_layer::{Adapter, DeltaLayerInner};
 use crate::context::RequestContext;
-use crate::page_cache::{self, PageReadGuard, ReadBufResult, PAGE_SZ};
+use crate::page_cache::{self, PageReadGuard, ReadBufResult, PAGE_SZ, PageWriteGuard};
 use crate::virtual_file::VirtualFile;
 use bytes::Bytes;
 use std::ops::{Deref, DerefMut};
@@ -169,7 +169,7 @@ impl FileBlockReader {
     }
 
     /// Read a page from the underlying file into given buffer.
-    async fn fill_buffer(&self, buf: &mut [u8], blkno: u32) -> Result<(), std::io::Error> {
+    async fn fill_buffer(&self, buf: PageWriteGuard<'static>, blkno: u32) -> Result<PageWriteGuard<'static>, std::io::Error> {
         assert!(buf.len() == PAGE_SZ);
         self.file
             .read_exact_at(buf, blkno as u64 * PAGE_SZ as u64)
@@ -198,7 +198,7 @@ impl FileBlockReader {
             ReadBufResult::Found(guard) => Ok(guard.into()),
             ReadBufResult::NotFound(mut write_guard) => {
                 // Read the page from disk into the buffer
-                self.fill_buffer(write_guard.deref_mut(), blknum).await?;
+                let write_guard = self.fill_buffer(write_guard, blknum).await?;
                 Ok(write_guard.mark_valid().into())
             }
         }

pageserver/src/tenant/ephemeral_file.rs

@@ -44,11 +44,11 @@ impl EphemeralFile {
                 "ephemeral-{filename_disambiguator}"
             )));
 
-        let file = VirtualFile::open_with_options(
-            &filename,
-            OpenOptions::new().read(true).write(true).create(true),
-        )
-        .await?;
+        let file = {
+            let mut options = tokio_epoll_uring::ops::open_at::OpenOptions::new();
+            options.read(true).write(true).create(true);
+            VirtualFile::open_with_options_async(&filename, options).await?
+        };
 
         Ok(EphemeralFile {
             page_cache_file_id: page_cache::next_file_id(),
@@ -89,10 +89,9 @@ impl EphemeralFile {
                     return Ok(BlockLease::PageReadGuard(guard))
                 }
                 page_cache::ReadBufResult::NotFound(mut write_guard) => {
-                    let buf: &mut [u8] = write_guard.deref_mut();
-                    debug_assert_eq!(buf.len(), PAGE_SZ);
-                    self.file
-                        .read_exact_at(&mut buf[..], blknum as u64 * PAGE_SZ as u64)
+                    let write_guard = self
+                        .file
+                        .read_exact_at(write_guard, blknum as u64 * PAGE_SZ as u64)
                         .await?;
                     let read_guard = write_guard.mark_valid();
                     return Ok(BlockLease::PageReadGuard(read_guard));

pageserver/src/tenant/mgr.rs

@@ -4,8 +4,10 @@
 use camino::{Utf8DirEntry, Utf8Path, Utf8PathBuf};
 use rand::{distributions::Alphanumeric, Rng};
 use std::collections::{hash_map, HashMap};
+use std::str::FromStr;
 use std::sync::Arc;
 use tokio::fs;
+use tokio::io::AsyncSeekExt;
 
 use anyhow::Context;
 use once_cell::sync::Lazy;
@@ -26,9 +28,11 @@ use crate::deletion_queue::DeletionQueueClient;
 use crate::task_mgr::{self, TaskKind};
 use crate::tenant::config::{AttachmentMode, LocationConf, LocationMode, TenantConfOpt};
 use crate::tenant::delete::DeleteTenantFlow;
+use crate::tenant::span::debug_assert_current_span_has_tenant_id;
+use crate::tenant::storage_layer::{DeltaLayer, ImageLayer, LayerFileName};
 use crate::tenant::{
-    create_tenant_files, AttachMarkerMode, AttachedTenantConf, CreateTenantFilesMode, Tenant,
-    TenantState,
+    create_tenant_files, remote_timeline_client, AttachMarkerMode, AttachedTenantConf,
+    CreateTenantFilesMode, IndexPart, Tenant, TenantState,
 };
 use crate::{InitializationOrder, IGNORED_TENANT_FILE_NAME, TEMP_FILE_SUFFIX};
 
@@ -695,6 +699,159 @@ pub(crate) async fn create_tenant(
     }).await
 }
 
+pub(crate) async fn duplicate_tenant(
+    conf: &'static PageServerConf,
+    tenant_conf: TenantConfOpt,
+    src_tenant_id: TenantId,
+    new_tenant_id: TenantId,
+    generation: Generation,
+    resources: TenantSharedResources,
+    ctx: &RequestContext,
+) -> Result<(), TenantMapInsertError> {
+    debug_assert_current_span_has_tenant_id();
+
+    // TODO: would be nice to use tenant_map_insert here, but, we're not ready to create a Tenant object yet
+    let tempdir = path_with_suffix_extension(
+        conf.tenants_path().join(&new_tenant_id.to_string()),
+        &format!("duplication.{TEMP_FILE_SUFFIX}"),
+    );
+    tokio::fs::remove_dir_all(&tempdir)
+        .await
+        .or_else(|e| match e.kind() {
+            std::io::ErrorKind::NotFound => Ok(()),
+            _ => Err(e),
+        })
+        .context("pre-run clean up tempdir")?;
+
+    tokio::fs::create_dir(&tempdir)
+        .await
+        .context("create tempdir")?;
+
+    // Copy the tenant's data in S3
+    let remote_storage = resources
+        .remote_storage
+        .as_ref()
+        .context("only works with remote storage")?;
+
+    let remote_src_timelines =
+        remote_timeline_client::list_remote_timelines(remote_storage, src_tenant_id)
+            .await
+            .context("list src timelines")?;
+
+    info!(?remote_src_timelines, "got src timelines");
+
+    for timeline_id in remote_src_timelines {
+        async {
+            let tempdir = tempdir.join(&timeline_id.to_string());
+
+            tokio::fs::create_dir(&tempdir)
+                .await
+                .context("create tempdir for timeline")?;
+
+            let remote_src_tl =
+                remote_timeline_client::remote_timeline_path(&src_tenant_id, &timeline_id);
+            let remote_dst_tl =
+                remote_timeline_client::remote_timeline_path(&new_tenant_id, &timeline_id);
+
+            let object_names = remote_storage
+                .list_prefixes(Some(&remote_src_tl))
+                .await
+                .context("list timeline remote prefix")?;
+
+            for name in object_names {
+                async {
+                    let name = name.object_name().context(
+                        "list_prefixes return values should always have object_name()=Some",
+                    )?;
+                    let remote_src_obj = remote_src_tl.join(name);
+                    let remote_dst_obj = remote_dst_tl.join(name);
+
+                    let tmp_obj_filepath = tempdir.join(name);
+                    let mut tmp_obj_file = tokio::fs::OpenOptions::new()
+                        .read(true)
+                        .write(true)
+                        .create_new(true)
+                        .open(&tmp_obj_filepath)
+                        .await
+                        .context("create temp file")?;
+                    let mut tmp_dl = remote_storage
+                        .download(&remote_src_obj)
+                        .await
+                        .context("start download")?;
+                    let tmp_obj_size =
+                        tokio::io::copy(&mut tmp_dl.download_stream, &mut tmp_obj_file)
+                            .await
+                            .context("do the download")?;
+
+                    if name == IndexPart::FILE_NAME {
+                        // needs no patching
+                    } else {
+                        let name = LayerFileName::from_str(name).map_err(|e: String| {
+                            anyhow::anyhow!("unknown key in timeline s3 prefix: {name:?}: {e}")
+                        })?;
+                        match name {
+                            LayerFileName::Image(_) => {
+                                ImageLayer::rewrite_tenant_timeline(
+                                    &tmp_obj_filepath,
+                                    new_tenant_id,
+                                    timeline_id, /* leave as is */
+                                    ctx,
+                                )
+                                .await
+                                .context("rewrite tenant timeline")?;
+                            }
+                            LayerFileName::Delta(_) => {
+                                DeltaLayer::rewrite_tenant_timeline(
+                                    &tmp_obj_filepath,
+                                    new_tenant_id,
+                                    timeline_id, /* leave as is */
+                                    ctx,
+                                )
+                                .await
+                                .context("rewrite tenant timeline")?;
+                            }
+                        }
+                    }
+
+                    info!(?remote_dst_obj, "uploading");
+
+                    tmp_obj_file
+                        .seek(std::io::SeekFrom::Start(0))
+                        .await
+                        .context("seek tmp file to beginning for upload")?;
+                    remote_storage
+                        .upload(
+                            tmp_obj_file,
+                            tmp_obj_size as usize,
+                            &remote_dst_obj,
+                            tmp_dl.metadata,
+                        )
+                        .await
+                        .context("upload modified")?;
+
+                    tokio::fs::remove_file(tmp_obj_filepath)
+                        .await
+                        .context("remove temp file")?;
+
+                    anyhow::Ok(())
+                }
+                .instrument(info_span!("copy object", object_name=?name))
+                .await
+                .context("copy object")?;
+            }
+            anyhow::Ok(())
+        }
+        .instrument(info_span!("copy_timeline", timeline_id=%timeline_id))
+        .await?;
+    }
+
+    tokio::fs::remove_dir_all(&tempdir)
+        .await
+        .context("post-run clean up tempdir")?;
+
+    attach_tenant(conf, new_tenant_id, generation, tenant_conf, resources, ctx).await
+}
+
 #[derive(Debug, thiserror::Error)]
 pub(crate) enum SetNewTenantConfigError {
     #[error(transparent)]

pageserver/src/tenant/storage_layer/delta_layer.rs

@@ -844,6 +844,49 @@ impl Drop for DeltaLayerWriter {
     }
 }
 
+impl DeltaLayer {
+    /// Assume the file at `path` is corrupt if this function returns with an error.
+    pub(crate) async fn rewrite_tenant_timeline(
+        path: &Utf8Path,
+        new_tenant: TenantId,
+        new_timeline: TimelineId,
+        ctx: &RequestContext,
+    ) -> anyhow::Result<()> {
+        let mut options = tokio_epoll_uring::ops::open_at::OpenOptions::new();
+            options.read(true)
+            .write(true);
+        let file = VirtualFile::open_with_options_async(path, options)
+            .await
+            .with_context(|| format!("Failed to open file '{}'", path))?;
+        let file = FileBlockReader::new(file);
+        let summary_blk = file.read_blk(0, ctx).await?;
+        let actual_summary = Summary::des_prefix(summary_blk.as_ref())?;
+        let mut file = file.file;
+        if actual_summary.magic != DELTA_FILE_MAGIC {
+            bail!("File '{}' is not a delta layer", path);
+        }
+        let new_summary = Summary {
+            tenant_id: new_tenant,
+            timeline_id: new_timeline,
+            ..actual_summary
+        };
+
+        let mut buf = smallvec::SmallVec::<[u8; PAGE_SZ]>::new();
+        Summary::ser_into(&new_summary, &mut buf)?;
+        if buf.spilled() {
+            // The code in ImageLayerWriterInner just warn!()s for this.
+            // It should probably error out as well.
+            anyhow::bail!(
+                "Used more than one page size for summary buffer: {}",
+                buf.len()
+            );
+        }
+        file.seek(SeekFrom::Start(0)).await?;
+        file.write_all(&buf).await?;
+        Ok(())
+    }
+}
+
 impl DeltaLayerInner {
     pub(super) async fn load(
         path: &Utf8Path,

pageserver/src/tenant/storage_layer/image_layer.rs

@@ -436,6 +436,48 @@ impl ImageLayer {
     }
 }
 
+impl ImageLayer {
+    /// Assume the file at `path` is corrupt if this function returns with an error.
+    pub(crate) async fn rewrite_tenant_timeline(
+        path: &Utf8Path,
+        new_tenant: TenantId,
+        new_timeline: TimelineId,
+        ctx: &RequestContext,
+    ) -> anyhow::Result<()> {
+        let mut options = tokio_epoll_uring::ops::open_at::OpenOptions::new();
+        options.read(true).write(true);
+        let file = VirtualFile::open_with_options_async(path, options)
+            .await
+            .with_context(|| format!("Failed to open file '{}'", path))?;
+        let file = FileBlockReader::new(file);
+        let summary_blk = file.read_blk(0, ctx).await?;
+        let actual_summary = Summary::des_prefix(summary_blk.as_ref())?;
+        let mut file = file.file;
+        if actual_summary.magic != IMAGE_FILE_MAGIC {
+            bail!("File '{}' is not a delta layer", path);
+        }
+        let new_summary = Summary {
+            tenant_id: new_tenant,
+            timeline_id: new_timeline,
+            ..actual_summary
+        };
+
+        let mut buf = smallvec::SmallVec::<[u8; PAGE_SZ]>::new();
+        Summary::ser_into(&new_summary, &mut buf)?;
+        if buf.spilled() {
+            // The code in ImageLayerWriterInner just warn!()s for this.
+            // It should probably error out as well.
+            anyhow::bail!(
+                "Used more than one page size for summary buffer: {}",
+                buf.len()
+            );
+        }
+        file.seek(SeekFrom::Start(0)).await?;
+        file.write_all(&buf).await?;
+        Ok(())
+    }
+}
+
 impl ImageLayerInner {
     pub(super) async fn load(
         path: &Utf8Path,
@@ -558,11 +600,11 @@ impl ImageLayerWriterInner {
             },
         );
         info!("new image layer {path}");
-        let mut file = VirtualFile::open_with_options(
-            &path,
-            std::fs::OpenOptions::new().write(true).create_new(true),
-        )
-        .await?;
+        let mut file = {
+            let mut options = tokio_epoll_uring::ops::open_at::OpenOptions::new();
+            options.write(true).create_new(true);
+            VirtualFile::open_with_options_async(&path, options).await?
+        };
         // make room for the header block
         file.seek(SeekFrom::Start(PAGE_SZ as u64)).await?;
         let blob_writer = BlobWriter::new(file, PAGE_SZ as u64);

pageserver/src/virtual_file.rs

@@ -11,14 +11,17 @@
 //! src/backend/storage/file/fd.c
 //!
 use crate::metrics::{StorageIoOperation, STORAGE_IO_SIZE, STORAGE_IO_TIME_METRIC};
+use crate::page_cache::PageWriteGuard;
 use crate::tenant::TENANTS_SEGMENT_NAME;
 use camino::{Utf8Path, Utf8PathBuf};
 use once_cell::sync::OnceCell;
 use std::fs::{self, File, OpenOptions};
 use std::io::{Error, ErrorKind, Seek, SeekFrom};
+use std::os::fd::{AsRawFd, FromRawFd, IntoRawFd, OwnedFd};
 use std::os::unix::fs::FileExt;
 use std::sync::atomic::{AtomicBool, AtomicUsize, Ordering};
-use std::sync::{RwLock, RwLockWriteGuard};
+use tokio::sync::{RwLock, RwLockReadGuard, RwLockWriteGuard};
+use tokio::time::Instant;
 
 ///
 /// A virtual file descriptor. You can use this just like std::fs::File, but internally
@@ -52,7 +55,7 @@ pub struct VirtualFile {
     /// opened, in the VirtualFile::create() function, and strip the flag before
     /// storing it here.
     pub path: Utf8PathBuf,
-    open_options: OpenOptions,
+    open_options: tokio_epoll_uring::ops::open_at::OpenOptions,
 
     // These are strings becase we only use them for metrics, and those expect strings.
     // It makes no sense for us to constantly turn the `TimelineId` and `TenantId` into
@@ -110,7 +113,7 @@ impl OpenFiles {
     ///
     /// On return, we hold a lock on the slot, and its 'tag' has been updated
     /// recently_used has been set. It's all ready for reuse.
-    fn find_victim_slot(&self) -> (SlotHandle, RwLockWriteGuard<SlotInner>) {
+    async fn find_victim_slot(&self) -> (SlotHandle, RwLockWriteGuard<SlotInner>) {
         //
         // Run the clock algorithm to find a slot to replace.
         //
@@ -142,7 +145,7 @@ impl OpenFiles {
                 }
                 retries += 1;
             } else {
-                slot_guard = slot.inner.write().unwrap();
+                slot_guard = slot.inner.write().await;
                 index = next;
                 break;
             }
@@ -153,7 +156,7 @@ impl OpenFiles {
         // old file.
         //
         if let Some(old_file) = slot_guard.file.take() {
-            // the normal path of dropping VirtualFile uses "close", use "close-by-replace" here to
+            // the normal path of dropping VirtualFile uses `Close`, use `CloseByReplace` here to
             // distinguish the two.
             STORAGE_IO_TIME_METRIC
                 .get(StorageIoOperation::CloseByReplace)
@@ -208,20 +211,43 @@ impl CrashsafeOverwriteError {
     }
 }
 
+/// Observe duration for the given storage I/O operation
+///
+/// Unlike `observe_closure_duration`, this supports async,
+/// where "support" means that we measure wall clock time.
+macro_rules! observe_duration {
+    ($op:expr, $($body:tt)*) => {{
+        let instant = Instant::now();
+        let result = $($body)*;
+        let elapsed = instant.elapsed().as_secs_f64();
+        STORAGE_IO_TIME_METRIC
+            .get($op)
+            .observe(elapsed);
+        result
+    }}
+}
+
+macro_rules! with_file {
+    ($this:expr, $op:expr, | $ident:ident | $($body:tt)*) => {{
+        let $ident = $this.lock_file().await?;
+        observe_duration!($op, $($body)*)
+    }};
+}
+
 impl VirtualFile {
     /// Open a file in read-only mode. Like File::open.
     pub async fn open(path: &Utf8Path) -> Result<VirtualFile, std::io::Error> {
-        Self::open_with_options(path, OpenOptions::new().read(true)).await
+        let mut options = tokio_epoll_uring::ops::open_at::OpenOptions::new();
+        options.read(true);
+        Self::open_with_options_async(path, options).await
     }
 
     /// Create a new file for writing. If the file exists, it will be truncated.
     /// Like File::create.
     pub async fn create(path: &Utf8Path) -> Result<VirtualFile, std::io::Error> {
-        Self::open_with_options(
-            path,
-            OpenOptions::new().write(true).create(true).truncate(true),
-        )
-        .await
+        let mut options = tokio_epoll_uring::ops::open_at::OpenOptions::new();
+        options.write(true).create(true).truncate(true);
+        Self::open_with_options_async(path, options).await
     }
 
     /// Open a file with given options.
@@ -229,6 +255,7 @@ impl VirtualFile {
     /// Note: If any custom flags were set in 'open_options' through OpenOptionsExt,
     /// they will be applied also when the file is subsequently re-opened, not only
     /// on the first time. Make sure that's sane!
+    #[cfg(test)]
     pub async fn open_with_options(
         path: &Utf8Path,
         open_options: &OpenOptions,
@@ -244,11 +271,9 @@ impl VirtualFile {
             tenant_id = "*".to_string();
             timeline_id = "*".to_string();
         }
-        let (handle, mut slot_guard) = get_open_files().find_victim_slot();
+        let (handle, mut slot_guard) = get_open_files().find_victim_slot().await;
 
-        let file = STORAGE_IO_TIME_METRIC
-            .get(StorageIoOperation::Open)
-            .observe_closure_duration(|| open_options.open(path))?;
+        let file = observe_duration!(StorageIoOperation::Open, open_options.open(path))?;
 
         // Strip all options other than read and write.
         //
@@ -293,16 +318,17 @@ impl VirtualFile {
             Err(e) if e.kind() == std::io::ErrorKind::NotFound => {}
             Err(e) => return Err(CrashsafeOverwriteError::RemovePreviousTempfile(e)),
         }
-        let mut file = Self::open_with_options(
-            tmp_path,
-            OpenOptions::new()
+        let mut file = {
+            let mut options = tokio_epoll_uring::ops::open_at::OpenOptions::new();
+            options
                 .write(true)
                 // Use `create_new` so that, if we race with ourselves or something else,
                 // we bail out instead of causing damage.
-                .create_new(true),
-        )
-        .await
-        .map_err(CrashsafeOverwriteError::CreateTempfile)?;
+                .create_new(true);
+            Self::open_with_options_async(tmp_path, options)
+                .await
+                .map_err(CrashsafeOverwriteError::CreateTempfile)?
+        };
         file.write_all(content)
             .await
             .map_err(CrashsafeOverwriteError::WriteContents)?;
@@ -318,10 +344,13 @@ impl VirtualFile {
         // the current `find_victim_slot` impl might pick the same slot for both
         // VirtualFile., and it eventually does a blocking write lock instead of
         // try_lock.
-        let final_parent_dirfd =
-            Self::open_with_options(final_path_parent, OpenOptions::new().read(true))
+        let final_parent_dirfd = {
+            let mut options = tokio_epoll_uring::ops::open_at::OpenOptions::new();
+            options.read(true);
+            Self::open_with_options_async(final_path_parent, options)
                 .await
-                .map_err(CrashsafeOverwriteError::OpenFinalPathParentDir)?;
+                .map_err(CrashsafeOverwriteError::OpenFinalPathParentDir)?
+        };
         final_parent_dirfd
             .sync_all()
             .await
@@ -329,24 +358,86 @@ impl VirtualFile {
         Ok(())
     }
 
+    /// Open a file with given options.
+    ///
+    /// Note: If any custom flags were set in 'open_options' through OpenOptionsExt,
+    /// they will be applied also when the file is subsequently re-opened, not only
+    /// on the first time. Make sure that's sane!
+    pub async fn open_with_options_async(
+        path: &Utf8Path,
+        open_options: tokio_epoll_uring::ops::open_at::OpenOptions,
+    ) -> Result<VirtualFile, std::io::Error> {
+        let path_str = path.to_string();
+        let parts = path_str.split('/').collect::<Vec<&str>>();
+        let tenant_id;
+        let timeline_id;
+        if parts.len() > 5 && parts[parts.len() - 5] == "tenants" {
+            tenant_id = parts[parts.len() - 4].to_string();
+            timeline_id = parts[parts.len() - 2].to_string();
+        } else {
+            tenant_id = "*".to_string();
+            timeline_id = "*".to_string();
+        }
+        let (handle, mut slot_guard) = get_open_files().find_victim_slot().await;
+
+        let file = {
+            let start = std::time::Instant::now();
+            let system = tokio_epoll_uring::thread_local_system().await;
+            let file: OwnedFd = system
+                .open(path, &open_options)
+                .await
+                .map_err(|e| match e {
+                    tokio_epoll_uring::Error::Op(e) => e,
+                    tokio_epoll_uring::Error::System(system) => {
+                        std::io::Error::new(std::io::ErrorKind::Other, system)
+                    }
+                })?;
+            let file = File::from(file);
+            file
+        };
+
+        // Strip all options other than read and write.
+        //
+        // It would perhaps be nicer to check just for the read and write flags
+        // explicitly, but OpenOptions doesn't contain any functions to read flags,
+        // only to set them.
+        let mut reopen_options = open_options;
+        reopen_options.create(false);
+        reopen_options.create_new(false);
+        reopen_options.truncate(false);
+
+        let vfile = VirtualFile {
+            handle: RwLock::new(handle),
+            pos: 0,
+            path: path.to_path_buf(),
+            open_options: reopen_options,
+            tenant_id,
+            timeline_id,
+        };
+
+        Ok(vfile)
+    }
+
     /// Call File::sync_all() on the underlying File.
     pub async fn sync_all(&self) -> Result<(), Error> {
-        self.with_file(StorageIoOperation::Fsync, |file| file.sync_all())
-            .await?
+        with_file!(self, StorageIoOperation::Fsync, |file| file
+            .as_ref()
+            .sync_all())
     }
 
     pub async fn metadata(&self) -> Result<fs::Metadata, Error> {
-        self.with_file(StorageIoOperation::Metadata, |file| file.metadata())
-            .await?
+        with_file!(self, StorageIoOperation::Metadata, |file| file
+            .as_ref()
+            .metadata())
     }
 
-    /// Helper function that looks up the underlying File for this VirtualFile,
-    /// opening it and evicting some other File if necessary. It calls 'func'
-    /// with the physical File.
-    async fn with_file<F, R>(&self, op: StorageIoOperation, mut func: F) -> Result<R, Error>
-    where
-        F: FnMut(&File) -> R,
-    {
+    /// Helper function internal to `VirtualFile` that looks up the underlying File,
+    /// opens it and evicts some other File if necessary. The passed parameter is
+    /// assumed to be a function available for the physical `File`.
+    ///
+    /// We are doing it via a macro as Rust doesn't support async closures that
+    /// take on parameters with lifetimes.
+    async fn lock_file(&self) -> Result<FileGuard<'static>, Error> {
         let open_files = get_open_files();
 
         let mut handle_guard = {
@@ -356,27 +447,23 @@ impl VirtualFile {
             // We only need to hold the handle lock while we read the current handle. If
             // another thread closes the file and recycles the slot for a different file,
             // we will notice that the handle we read is no longer valid and retry.
-            let mut handle = *self.handle.read().unwrap();
+            let mut handle = *self.handle.read().await;
             loop {
                 // Check if the slot contains our File
                 {
                     let slot = &open_files.slots[handle.index];
-                    let slot_guard = slot.inner.read().unwrap();
-                    if slot_guard.tag == handle.tag {
-                        if let Some(file) = &slot_guard.file {
-                            // Found a cached file descriptor.
-                            slot.recently_used.store(true, Ordering::Relaxed);
-                            return Ok(STORAGE_IO_TIME_METRIC
-                                .get(op)
-                                .observe_closure_duration(|| func(file)));
-                        }
+                    let slot_guard = slot.inner.read().await;
+                    if slot_guard.tag == handle.tag && slot_guard.file.is_some() {
+                        // Found a cached file descriptor.
+                        slot.recently_used.store(true, Ordering::Relaxed);
+                        return Ok(FileGuard { slot_guard });
                     }
                 }
 
                 // The slot didn't contain our File. We will have to open it ourselves,
                 // but before that, grab a write lock on handle in the VirtualFile, so
                 // that no other thread will try to concurrently open the same file.
-                let handle_guard = self.handle.write().unwrap();
+                let handle_guard = self.handle.write().await;
 
                 // If another thread changed the handle while we were not holding the lock,
                 // then the handle might now be valid again. Loop back to retry.
@@ -390,17 +477,24 @@ impl VirtualFile {
 
         // We need to open the file ourselves. The handle in the VirtualFile is
         // now locked in write-mode. Find a free slot to put it in.
-        let (handle, mut slot_guard) = open_files.find_victim_slot();
+        let (handle, mut slot_guard) = open_files.find_victim_slot().await;
 
         // Open the physical file
-        let file = STORAGE_IO_TIME_METRIC
-            .get(StorageIoOperation::Open)
-            .observe_closure_duration(|| self.open_options.open(&self.path))?;
-
-        // Perform the requested operation on it
-        let result = STORAGE_IO_TIME_METRIC
-            .get(op)
-            .observe_closure_duration(|| func(&file));
+        let file = {
+            let system = tokio_epoll_uring::thread_local_system().await;
+            let file: OwnedFd =
+                system
+                    .open(&self.path, &self.open_options)
+                    .await
+                    .map_err(|e| match e {
+                        tokio_epoll_uring::Error::Op(e) => e,
+                        tokio_epoll_uring::Error::System(system) => {
+                            std::io::Error::new(std::io::ErrorKind::Other, system)
+                        }
+                    })?;
+            let file = File::from(file);
+            file
+        };
 
         // Store the File in the slot and update the handle in the VirtualFile
         // to point to it.
@@ -408,7 +502,9 @@ impl VirtualFile {
 
         *handle_guard = handle;
 
-        Ok(result)
+        return Ok(FileGuard {
+            slot_guard: slot_guard.downgrade(),
+        });
     }
 
     pub fn remove(self) {
@@ -423,11 +519,9 @@ impl VirtualFile {
                 self.pos = offset;
             }
             SeekFrom::End(offset) => {
-                self.pos = self
-                    .with_file(StorageIoOperation::Seek, |mut file| {
-                        file.seek(SeekFrom::End(offset))
-                    })
-                    .await??
+                self.pos = with_file!(self, StorageIoOperation::Seek, |file| file
+                    .as_ref()
+                    .seek(SeekFrom::End(offset)))?
             }
             SeekFrom::Current(offset) => {
                 let pos = self.pos as i128 + offset as i128;
@@ -447,24 +541,59 @@ impl VirtualFile {
     }
 
     // Copied from https://doc.rust-lang.org/1.72.0/src/std/os/unix/fs.rs.html#117-135
-    pub async fn read_exact_at(&self, mut buf: &mut [u8], mut offset: u64) -> Result<(), Error> {
-        while !buf.is_empty() {
-            match self.read_at(buf, offset).await {
-                Ok(0) => {
-                    return Err(Error::new(
-                        std::io::ErrorKind::UnexpectedEof,
-                        "failed to fill whole buffer",
-                    ))
-                }
-                Ok(n) => {
-                    buf = &mut buf[n..];
-                    offset += n as u64;
-                }
-                Err(ref e) if e.kind() == std::io::ErrorKind::Interrupted => {}
-                Err(e) => return Err(e),
+    pub async fn read_exact_at(
+        &self,
+        mut write_guard: PageWriteGuard<'static>,
+        mut offset: u64,
+    ) -> Result<PageWriteGuard<'static>, Error> {
+        let file_guard: FileGuard<'static> = self.lock_file().await?;
+
+        let system = tokio_epoll_uring::thread_local_system().await;
+        struct PageWriteGuardBuf {
+            buf: PageWriteGuard<'static>,
+            init_up_to: usize,
+        }
+        unsafe impl tokio_epoll_uring::IoBuf for PageWriteGuardBuf {
+            fn stable_ptr(&self) -> *const u8 {
+                self.buf.as_ptr()
+            }
+            fn bytes_init(&self) -> usize {
+                self.init_up_to
+            }
+            fn bytes_total(&self) -> usize {
+                self.buf.len()
             }
         }
-        Ok(())
+        unsafe impl tokio_epoll_uring::IoBufMut for PageWriteGuardBuf {
+            fn stable_mut_ptr(&mut self) -> *mut u8 {
+                self.buf.as_mut_ptr()
+            }
+
+            unsafe fn set_init(&mut self, pos: usize) {
+                assert!(pos <= self.buf.len());
+                self.init_up_to = pos;
+            }
+        }
+        let buf = PageWriteGuardBuf {
+            buf: write_guard,
+            init_up_to: 0,
+        };
+        let owned_fd = unsafe { OwnedFd::from_raw_fd(file_guard.as_ref().as_raw_fd()) };
+        let guard = scopeguard::guard(file_guard, |_| {
+            panic!("must not drop future while operation is ongoing (todo: pass file_guard to tokio_epoll_uring to aovid this)")
+        });
+        let ((owned_fd, buf), res) = system.read(owned_fd, offset, buf).await;
+        let _ = OwnedFd::into_raw_fd(owned_fd);
+        let _ = scopeguard::ScopeGuard::into_inner(guard);
+        let PageWriteGuardBuf {
+            buf: write_guard,
+            init_up_to,
+        } = buf;
+        if let Ok(num_read) = res {
+            assert!(init_up_to == num_read); // TODO need to deal with short reads here
+        }
+        res.map(|_| write_guard)
+            .map_err(|e| Error::new(ErrorKind::Other, e))
     }
 
     // Copied from https://doc.rust-lang.org/1.72.0/src/std/os/unix/fs.rs.html#219-235
@@ -514,22 +643,10 @@ impl VirtualFile {
         Ok(n)
     }
 
-    pub async fn read_at(&self, buf: &mut [u8], offset: u64) -> Result<usize, Error> {
-        let result = self
-            .with_file(StorageIoOperation::Read, |file| file.read_at(buf, offset))
-            .await?;
-        if let Ok(size) = result {
-            STORAGE_IO_SIZE
-                .with_label_values(&["read", &self.tenant_id, &self.timeline_id])
-                .add(size as i64);
-        }
-        result
-    }
-
     async fn write_at(&self, buf: &[u8], offset: u64) -> Result<usize, Error> {
-        let result = self
-            .with_file(StorageIoOperation::Write, |file| file.write_at(buf, offset))
-            .await?;
+        let result = with_file!(self, StorageIoOperation::Write, |file| file
+            .as_ref()
+            .write_at(buf, offset));
         if let Ok(size) = result {
             STORAGE_IO_SIZE
                 .with_label_values(&["write", &self.tenant_id, &self.timeline_id])
@@ -539,6 +656,18 @@ impl VirtualFile {
     }
 }
 
+struct FileGuard<'a> {
+    slot_guard: RwLockReadGuard<'a, SlotInner>,
+}
+
+impl<'a> AsRef<File> for FileGuard<'a> {
+    fn as_ref(&self) -> &File {
+        // This unwrap is safe because we only create `FileGuard`s
+        // if we know that the file is Some.
+        self.slot_guard.file.as_ref().unwrap()
+    }
+}
+
 #[cfg(test)]
 impl VirtualFile {
     pub(crate) async fn read_blk(
@@ -571,20 +700,39 @@ impl VirtualFile {
 impl Drop for VirtualFile {
     /// If a VirtualFile is dropped, close the underlying file if it was open.
     fn drop(&mut self) {
-        let handle = self.handle.get_mut().unwrap();
+        let handle = self.handle.get_mut();
 
-        // We could check with a read-lock first, to avoid waiting on an
-        // unrelated I/O.
-        let slot = &get_open_files().slots[handle.index];
-        let mut slot_guard = slot.inner.write().unwrap();
-        if slot_guard.tag == handle.tag {
-            slot.recently_used.store(false, Ordering::Relaxed);
-            // there is also operation "close-by-replace" for closes done on eviction for
-            // comparison.
-            STORAGE_IO_TIME_METRIC
-                .get(StorageIoOperation::Close)
-                .observe_closure_duration(|| drop(slot_guard.file.take()));
+        fn clean_slot(slot: &Slot, mut slot_guard: RwLockWriteGuard<'_, SlotInner>, tag: u64) {
+            if slot_guard.tag == tag {
+                slot.recently_used.store(false, Ordering::Relaxed);
+                // there is also the `CloseByReplace` operation for closes done on eviction for
+                // comparison.
+                STORAGE_IO_TIME_METRIC
+                    .get(StorageIoOperation::Close)
+                    .observe_closure_duration(|| drop(slot_guard.file.take()));
+            }
         }
+
+        // We don't have async drop so we cannot directly await the lock here.
+        // Instead, first do a best-effort attempt at closing the underlying
+        // file descriptor by using `try_write`, and if that fails, spawn
+        // a tokio task to do it asynchronously: we just want it to be
+        // cleaned up eventually.
+        // Most of the time, the `try_lock` should succeed though,
+        // as we have `&mut self` access. In other words, if the slot
+        // is still occupied by our file, there should be no access from
+        // other I/O operations; the only other possible place to lock
+        // the slot is the lock algorithm looking for free slots.
+        let slot = &get_open_files().slots[handle.index];
+        if let Ok(slot_guard) = slot.inner.try_write() {
+            clean_slot(slot, slot_guard, handle.tag);
+        } else {
+            let tag = handle.tag;
+            tokio::spawn(async move {
+                let slot_guard = slot.inner.write().await;
+                clean_slot(slot, slot_guard, tag);
+            });
+        };
     }
 }
 

test_runner/duplicate_tenant.py

@@ -0,0 +1,43 @@
+# Usage from top of repo:
+#  poetry run python3 test_runner/duplicate_tenant.py b97965931096047b2d54958756baee7b 10
+from queue import Queue
+import sys
+import threading
+
+import requests
+from fixtures.pageserver.http import PageserverHttpClient
+from fixtures.types import TenantId
+
+initial_tenant = sys.argv[1]
+ncopies = int(sys.argv[2])
+numthreads = int(sys.argv[3])
+
+
+# class DuckTypedNeonEnv:
+#     pass
+
+
+# cli = NeonCli(DuckTypedNeonEnv())
+
+q = Queue()
+for i in range(0, ncopies):
+    q.put(i)
+
+for i in range(0, numthreads):
+    q.put(None)
+
+
+def create():
+    while True:
+        if q.get() == None:
+            break
+        new_tenant = TenantId.generate()
+        res = requests.post(
+            f"http://localhost:9898/v1/tenant/{initial_tenant}/duplicate",
+            json={"new_tenant_id": str(new_tenant)},
+        )
+        res.raise_for_status()
+
+
+for i in range(0, numthreads):
+    threading.Thread(target=create).start()

test_runner/fixtures/pageserver/http.py

@@ -215,6 +215,25 @@ class PageserverHttpClient(requests.Session):
         assert isinstance(new_tenant_id, str)
         return TenantId(new_tenant_id)
 
+    def tenant_duplicate(
+        self, src_tenant_id: TenantId, new_tenant_id: TenantId, conf: Optional[Dict[str, Any]] = None
+    ) -> TenantId:
+        if conf is not None:
+            assert "new_tenant_id" not in conf.keys()
+        res = self.post(
+            f"http://localhost:{self.port}/v1/tenant/{src_tenant_id}/duplicate",
+            json={
+                "new_tenant_id": str(new_tenant_id),
+                **(conf or {}),
+            },
+        )
+        self.verbose_error(res)
+        if res.status_code == 409:
+            raise Exception(f"could not create tenant: already exists for id {new_tenant_id}")
+        new_tenant_id = res.json()
+        assert isinstance(new_tenant_id, str)
+        return TenantId(new_tenant_id)
+
     def tenant_attach(
         self,
         tenant_id: TenantId,

test_runner/regress/test_tenant_duplicate.py

@@ -0,0 +1,54 @@
+import time
+from fixtures.neon_fixtures import (
+    NeonEnvBuilder,
+    last_flush_lsn_upload,
+)
+from fixtures.remote_storage import (
+    RemoteStorageKind,
+)
+from fixtures.types import TenantId
+from fixtures.log_helper import log
+
+
+def test_tenant_duplicate(
+    neon_env_builder: NeonEnvBuilder,
+):
+    neon_env_builder.enable_pageserver_remote_storage(RemoteStorageKind.LOCAL_FS)
+
+    env = neon_env_builder.init_start()
+
+    with env.endpoints.create_start("main", tenant_id=env.initial_tenant) as ep_main:
+        ep_main.safe_psql("CREATE TABLE foo (i int);")
+        ep_main.safe_psql("INSERT INTO foo VALUES (1), (2), (3);")
+        last_flush_lsn = last_flush_lsn_upload(
+            env, ep_main, env.initial_tenant, env.initial_timeline
+        )
+
+    new_tenant_id = TenantId.generate()
+    # timeline id remains unchanged with tenant_duplicate
+    # TODO: implement a remapping scheme so timeline ids remain globally unique
+    new_timeline_id = env.initial_timeline
+
+    log.info(f"Duplicate tenant/timeline will be: {new_tenant_id}/{new_timeline_id}")
+
+    ps_http = env.pageserver.http_client()
+
+    ps_http.tenant_duplicate(env.initial_tenant, new_tenant_id)
+
+    ps_http.tenant_delete(env.initial_tenant)
+
+    env.neon_cli.map_branch("duplicate", new_tenant_id, new_timeline_id)
+
+    # start read-only replicate and validate
+    with env.endpoints.create_start(
+        "duplicate", tenant_id=new_tenant_id, lsn=last_flush_lsn
+    ) as ep_dup:
+        with ep_dup.connect() as conn:
+            with conn.cursor() as cur:
+                cur.execute("SELECT * FROM foo ORDER BY i;")
+                cur.fetchall() == [(1,), (2,), (3,)]
+
+    # ensure restarting PS works
+    env.pageserver.stop()
+    env.pageserver.start()
+