pageserver: add direct io config to virtual file (#9214)

## Problem
We need a way to incrementally switch to direct IO. During the rollout
we might want to switch to O_DIRECT on image and delta layer read path
first before others.

## Summary of changes
- Revisited and simplified direct io config in `PageserverConf`. 
- We could add a fallback mode for open, but for read there isn't a
reasonable alternative (without creating another buffered virtual file).
- Added a wrapper around `VirtualFile`, current implementation become
`VirtualFileInner`
- Use `open_v2`, `create_v2`, `open_with_options_v2` when we want to use
the IO mode specified in PS config.
- Once we onboard all IO through VirtualFile using this new API, we will
delete the old code path.
- Make io mode live configurable for benchmarking.
- Only guaranteed for files opened after the config change, so do it
before the experiment.

As an example, we are using `open_v2` with
`virtual_file::IoMode::Direct` in
#9169

We also remove `io_buffer_alignment` config in
a04cfd7 and use it as a compile time
constant. This way we don't have to carry the alignment around or make
frequent call to retrieve this information from the static variable.

Signed-off-by: Yuchen Liang <[email protected]>

libs/pageserver_api/src/config.rs

@@ -104,8 +104,7 @@ pub struct ConfigToml {
     pub image_compression: ImageCompressionAlgorithm,
     pub ephemeral_bytes_per_memory_kb: usize,
     pub l0_flush: Option<crate::models::L0FlushConfig>,
-    pub virtual_file_direct_io: crate::models::virtual_file::DirectIoMode,
-    pub io_buffer_alignment: usize,
+    pub virtual_file_io_mode: Option<crate::models::virtual_file::IoMode>,
 }
 
 #[derive(Debug, Clone, PartialEq, Eq, serde::Serialize, serde::Deserialize)]
@@ -388,10 +387,7 @@ impl Default for ConfigToml {
             image_compression: (DEFAULT_IMAGE_COMPRESSION),
             ephemeral_bytes_per_memory_kb: (DEFAULT_EPHEMERAL_BYTES_PER_MEMORY_KB),
             l0_flush: None,
-            virtual_file_direct_io: crate::models::virtual_file::DirectIoMode::default(),
-
-            io_buffer_alignment: DEFAULT_IO_BUFFER_ALIGNMENT,
-
+            virtual_file_io_mode: None,
             tenant_config: TenantConfigToml::default(),
         }
     }

libs/pageserver_api/src/models.rs

@@ -972,8 +972,6 @@ pub struct TopTenantShardsResponse {
 }
 
 pub mod virtual_file {
-    use std::path::PathBuf;
-
     #[derive(
         Copy,
         Clone,
@@ -994,50 +992,45 @@ pub mod virtual_file {
     }
 
     /// Direct IO modes for a pageserver.
-    #[derive(Debug, PartialEq, Eq, Clone, serde::Deserialize, serde::Serialize, Default)]
-    #[serde(tag = "mode", rename_all = "kebab-case", deny_unknown_fields)]
-    pub enum DirectIoMode {
-        /// Direct IO disabled (uses usual buffered IO).
-        #[default]
-        Disabled,
-        /// Direct IO disabled (performs checks and perf simulations).
-        Evaluate {
-            /// Alignment check level
-            alignment_check: DirectIoAlignmentCheckLevel,
-            /// Latency padded for performance simulation.
-            latency_padding: DirectIoLatencyPadding,
-        },
-        /// Direct IO enabled.
-        Enabled {
-            /// Actions to perform on alignment error.
-            on_alignment_error: DirectIoOnAlignmentErrorAction,
-        },
+    #[derive(
+        Copy,
+        Clone,
+        PartialEq,
+        Eq,
+        Hash,
+        strum_macros::EnumString,
+        strum_macros::Display,
+        serde_with::DeserializeFromStr,
+        serde_with::SerializeDisplay,
+        Debug,
+    )]
+    #[strum(serialize_all = "kebab-case")]
+    #[repr(u8)]
+    pub enum IoMode {
+        /// Uses buffered IO.
+        Buffered,
+        /// Uses direct IO, error out if the operation fails.
+        #[cfg(target_os = "linux")]
+        Direct,
     }
 
-    #[derive(Debug, PartialEq, Eq, Clone, serde::Deserialize, serde::Serialize, Default)]
-    #[serde(rename_all = "kebab-case")]
-    pub enum DirectIoAlignmentCheckLevel {
-        #[default]
-        Error,
-        Log,
-        None,
+    impl IoMode {
+        pub const fn preferred() -> Self {
+            Self::Buffered
+        }
     }
 
-    #[derive(Debug, PartialEq, Eq, Clone, serde::Deserialize, serde::Serialize, Default)]
-    #[serde(rename_all = "kebab-case")]
-    pub enum DirectIoOnAlignmentErrorAction {
-        Error,
-        #[default]
-        FallbackToBuffered,
-    }
+    impl TryFrom<u8> for IoMode {
+        type Error = u8;
 
-    #[derive(Debug, PartialEq, Eq, Clone, serde::Deserialize, serde::Serialize, Default)]
-    #[serde(tag = "type", rename_all = "kebab-case")]
-    pub enum DirectIoLatencyPadding {
-        /// Pad virtual file operations with IO to a fake file.
-        FakeFileRW { path: PathBuf },
-        #[default]
-        None,
+        fn try_from(value: u8) -> Result<Self, Self::Error> {
+            Ok(match value {
+                v if v == (IoMode::Buffered as u8) => IoMode::Buffered,
+                #[cfg(target_os = "linux")]
+                v if v == (IoMode::Direct as u8) => IoMode::Direct,
+                x => return Err(x),
+            })
+        }
     }
 }
 

pageserver/benches/bench_ingest.rs

@@ -164,11 +164,7 @@ fn criterion_benchmark(c: &mut Criterion) {
     let conf: &'static PageServerConf = Box::leak(Box::new(
         pageserver::config::PageServerConf::dummy_conf(temp_dir.path().to_path_buf()),
     ));
-    virtual_file::init(
-        16384,
-        virtual_file::io_engine_for_bench(),
-        pageserver_api::config::defaults::DEFAULT_IO_BUFFER_ALIGNMENT,
-    );
+    virtual_file::init(16384, virtual_file::io_engine_for_bench());
     page_cache::init(conf.page_cache_size);
 
     {

pageserver/client/src/mgmt_api.rs

@@ -540,10 +540,13 @@ impl Client {
             .map_err(Error::ReceiveBody)
     }
 
-    /// Configs io buffer alignment at runtime.
-    pub async fn put_io_alignment(&self, align: usize) -> Result<()> {
-        let uri = format!("{}/v1/io_alignment", self.mgmt_api_endpoint);
-        self.request(Method::PUT, uri, align)
+    /// Configs io mode at runtime.
+    pub async fn put_io_mode(
+        &self,
+        mode: &pageserver_api::models::virtual_file::IoMode,
+    ) -> Result<()> {
+        let uri = format!("{}/v1/io_mode", self.mgmt_api_endpoint);
+        self.request(Method::PUT, uri, mode)
             .await?
             .json()
             .await

pageserver/ctl/src/layer_map_analyzer.rs

@@ -152,11 +152,7 @@ pub(crate) async fn main(cmd: &AnalyzeLayerMapCmd) -> Result<()> {
     let ctx = RequestContext::new(TaskKind::DebugTool, DownloadBehavior::Error);
 
     // Initialize virtual_file (file desriptor cache) and page cache which are needed to access layer persistent B-Tree.
-    pageserver::virtual_file::init(
-        10,
-        virtual_file::api::IoEngineKind::StdFs,
-        pageserver_api::config::defaults::DEFAULT_IO_BUFFER_ALIGNMENT,
-    );
+    pageserver::virtual_file::init(10, virtual_file::api::IoEngineKind::StdFs);
     pageserver::page_cache::init(100);
 
     let mut total_delta_layers = 0usize;

pageserver/ctl/src/layers.rs

@@ -59,7 +59,7 @@ pub(crate) enum LayerCmd {
 
 async fn read_delta_file(path: impl AsRef<Path>, ctx: &RequestContext) -> Result<()> {
     let path = Utf8Path::from_path(path.as_ref()).expect("non-Unicode path");
-    virtual_file::init(10, virtual_file::api::IoEngineKind::StdFs, 1);
+    virtual_file::init(10, virtual_file::api::IoEngineKind::StdFs);
     page_cache::init(100);
     let file = VirtualFile::open(path, ctx).await?;
     let file_id = page_cache::next_file_id();
@@ -190,11 +190,7 @@ pub(crate) async fn main(cmd: &LayerCmd) -> Result<()> {
             new_tenant_id,
             new_timeline_id,
         } => {
-            pageserver::virtual_file::init(
-                10,
-                virtual_file::api::IoEngineKind::StdFs,
-                pageserver_api::config::defaults::DEFAULT_IO_BUFFER_ALIGNMENT,
-            );
+            pageserver::virtual_file::init(10, virtual_file::api::IoEngineKind::StdFs);
             pageserver::page_cache::init(100);
 
             let ctx = RequestContext::new(TaskKind::DebugTool, DownloadBehavior::Error);

pageserver/ctl/src/main.rs

@@ -26,7 +26,7 @@ use pageserver::{
     tenant::{dump_layerfile_from_path, metadata::TimelineMetadata},
     virtual_file,
 };
-use pageserver_api::{config::defaults::DEFAULT_IO_BUFFER_ALIGNMENT, shard::TenantShardId};
+use pageserver_api::shard::TenantShardId;
 use postgres_ffi::ControlFileData;
 use remote_storage::{RemotePath, RemoteStorageConfig};
 use tokio_util::sync::CancellationToken;
@@ -205,11 +205,7 @@ fn read_pg_control_file(control_file_path: &Utf8Path) -> anyhow::Result<()> {
 
 async fn print_layerfile(path: &Utf8Path) -> anyhow::Result<()> {
     // Basic initialization of things that don't change after startup
-    virtual_file::init(
-        10,
-        virtual_file::api::IoEngineKind::StdFs,
-        DEFAULT_IO_BUFFER_ALIGNMENT,
-    );
+    virtual_file::init(10, virtual_file::api::IoEngineKind::StdFs);
     page_cache::init(100);
     let ctx = RequestContext::new(TaskKind::DebugTool, DownloadBehavior::Error);
     dump_layerfile_from_path(path, true, &ctx).await

pageserver/pagebench/src/cmd/getpage_latest_lsn.rs

@@ -59,9 +59,9 @@ pub(crate) struct Args {
     #[clap(long)]
     set_io_engine: Option<pageserver_api::models::virtual_file::IoEngineKind>,
 
-    /// Before starting the benchmark, live-reconfigure the pageserver to use specified alignment for io buffers.
+    /// Before starting the benchmark, live-reconfigure the pageserver to use specified io mode (buffered vs. direct).
     #[clap(long)]
-    set_io_alignment: Option<usize>,
+    set_io_mode: Option<pageserver_api::models::virtual_file::IoMode>,
 
     targets: Option<Vec<TenantTimelineId>>,
 }
@@ -129,8 +129,8 @@ async fn main_impl(
         mgmt_api_client.put_io_engine(engine_str).await?;
     }
 
-    if let Some(align) = args.set_io_alignment {
-        mgmt_api_client.put_io_alignment(align).await?;
+    if let Some(mode) = &args.set_io_mode {
+        mgmt_api_client.put_io_mode(mode).await?;
     }
 
     // discover targets

pageserver/src/bin/pageserver.rs

@@ -125,8 +125,7 @@ fn main() -> anyhow::Result<()> {
 
     // after setting up logging, log the effective IO engine choice and read path implementations
     info!(?conf.virtual_file_io_engine, "starting with virtual_file IO engine");
-    info!(?conf.virtual_file_direct_io, "starting with virtual_file Direct IO settings");
-    info!(?conf.io_buffer_alignment, "starting with setting for IO buffer alignment");
+    info!(?conf.virtual_file_io_mode, "starting with virtual_file IO mode");
 
     // The tenants directory contains all the pageserver local disk state.
     // Create if not exists and make sure all the contents are durable before proceeding.
@@ -168,11 +167,7 @@ fn main() -> anyhow::Result<()> {
     let scenario = failpoint_support::init();
 
     // Basic initialization of things that don't change after startup
-    virtual_file::init(
-        conf.max_file_descriptors,
-        conf.virtual_file_io_engine,
-        conf.io_buffer_alignment,
-    );
+    virtual_file::init(conf.max_file_descriptors, conf.virtual_file_io_engine);
     page_cache::init(conf.page_cache_size);
 
     start_pageserver(launch_ts, conf).context("Failed to start pageserver")?;

pageserver/src/config.rs

@@ -174,9 +174,7 @@ pub struct PageServerConf {
     pub l0_flush: crate::l0_flush::L0FlushConfig,
 
     /// Direct IO settings
-    pub virtual_file_direct_io: virtual_file::DirectIoMode,
-
-    pub io_buffer_alignment: usize,
+    pub virtual_file_io_mode: virtual_file::IoMode,
 }
 
 /// Token for authentication to safekeepers
@@ -325,11 +323,10 @@ impl PageServerConf {
             image_compression,
             ephemeral_bytes_per_memory_kb,
             l0_flush,
-            virtual_file_direct_io,
+            virtual_file_io_mode,
             concurrent_tenant_warmup,
             concurrent_tenant_size_logical_size_queries,
             virtual_file_io_engine,
-            io_buffer_alignment,
             tenant_config,
         } = config_toml;
 
@@ -368,8 +365,6 @@ impl PageServerConf {
             max_vectored_read_bytes,
             image_compression,
             ephemeral_bytes_per_memory_kb,
-            virtual_file_direct_io,
-            io_buffer_alignment,
 
             // ------------------------------------------------------------
             // fields that require additional validation or custom handling
@@ -408,6 +403,7 @@ impl PageServerConf {
             l0_flush: l0_flush
                 .map(crate::l0_flush::L0FlushConfig::from)
                 .unwrap_or_default(),
+            virtual_file_io_mode: virtual_file_io_mode.unwrap_or(virtual_file::IoMode::preferred()),
         };
 
         // ------------------------------------------------------------

pageserver/src/http/routes.rs

@@ -17,6 +17,7 @@ use hyper::header;
 use hyper::StatusCode;
 use hyper::{Body, Request, Response, Uri};
 use metrics::launch_timestamp::LaunchTimestamp;
+use pageserver_api::models::virtual_file::IoMode;
 use pageserver_api::models::AuxFilePolicy;
 use pageserver_api::models::DownloadRemoteLayersTaskSpawnRequest;
 use pageserver_api::models::IngestAuxFilesRequest;
@@ -2381,17 +2382,13 @@ async fn put_io_engine_handler(
     json_response(StatusCode::OK, ())
 }
 
-async fn put_io_alignment_handler(
+async fn put_io_mode_handler(
     mut r: Request<Body>,
     _cancel: CancellationToken,
 ) -> Result<Response<Body>, ApiError> {
     check_permission(&r, None)?;
-    let align: usize = json_request(&mut r).await?;
-    crate::virtual_file::set_io_buffer_alignment(align).map_err(|align| {
-        ApiError::PreconditionFailed(
-            format!("Requested io alignment ({align}) is not a power of two").into(),
-        )
-    })?;
+    let mode: IoMode = json_request(&mut r).await?;
+    crate::virtual_file::set_io_mode(mode);
     json_response(StatusCode::OK, ())
 }
 
@@ -3082,9 +3079,7 @@ pub fn make_router(
             |r| api_handler(r, timeline_collect_keyspace),
         )
         .put("/v1/io_engine", |r| api_handler(r, put_io_engine_handler))
-        .put("/v1/io_alignment", |r| {
-            api_handler(r, put_io_alignment_handler)
-        })
+        .put("/v1/io_mode", |r| api_handler(r, put_io_mode_handler))
         .put(
             "/v1/tenant/:tenant_shard_id/timeline/:timeline_id/force_aux_policy_switch",
             |r| api_handler(r, force_aux_policy_switch_handler),

pageserver/src/tenant/ephemeral_file.rs

@@ -84,7 +84,7 @@ impl Drop for EphemeralFile {
     fn drop(&mut self) {
         // unlink the file
         // we are clear to do this, because we have entered a gate
-        let path = &self.buffered_writer.as_inner().as_inner().path;
+        let path = self.buffered_writer.as_inner().as_inner().path();
         let res = std::fs::remove_file(path);
         if let Err(e) = res {
             if e.kind() != std::io::ErrorKind::NotFound {
@@ -356,7 +356,7 @@ mod tests {
         }
 
         let file_contents =
-            std::fs::read(&file.buffered_writer.as_inner().as_inner().path).unwrap();
+            std::fs::read(file.buffered_writer.as_inner().as_inner().path()).unwrap();
         assert_eq!(file_contents, &content[0..cap]);
 
         let buffer_contents = file.buffered_writer.inspect_buffer();
@@ -392,7 +392,7 @@ mod tests {
             .buffered_writer
             .as_inner()
             .as_inner()
-            .path
+            .path()
             .metadata()
             .unwrap();
         assert_eq!(