builder: delay free data structure to reduce image build time

According to perf flame graph, it takes a long time to free objects
used by image builder. In most common cases, the builder will only
run once and exit, so it's unnecessary to free those used objects.

Signed-off-by: Jiang Liu <[email protected]>

rafs/src/builder/core/tree.rs

@@ -22,7 +22,7 @@ use std::path::{Path, PathBuf};
 use std::sync::{Arc, Mutex, MutexGuard};
 
 use anyhow::{bail, Result};
-use nydus_utils::{root_tracer, timing_tracer};
+use nydus_utils::{lazy_drop, root_tracer, timing_tracer};
 
 use super::node::{ChunkSource, Node, NodeChunk, NodeInfo};
 use super::overlay::{Overlay, WhiteoutType};
@@ -180,8 +180,10 @@ impl Tree {
         // Handle the root node.
         upper.lock_node().overlay = Overlay::UpperModification;
         self.node = upper.node.clone();
+        self.merge_children(ctx, &upper)?;
+        lazy_drop(upper);
 
-        self.merge_children(ctx, &upper)
+        Ok(())
     }
 
     fn merge_children(&mut self, ctx: &BuildContext, upper: &Tree) -> Result<()> {

rafs/src/builder/directory.rs

@@ -6,7 +6,7 @@ use std::fs;
 use std::fs::DirEntry;
 
 use anyhow::{anyhow, Context, Result};
-use nydus_utils::{event_tracer, root_tracer, timing_tracer};
+use nydus_utils::{event_tracer, lazy_drop, root_tracer, timing_tracer};
 
 use super::core::blob::Blob;
 use super::core::context::{
@@ -190,6 +190,8 @@ impl Builder for DirectoryBuilder {
             )?;
         }
 
+        lazy_drop(bootstrap_ctx);
+
         BuildOutput::new(blob_mgr, &bootstrap_mgr.bootstrap_storage)
     }
 }

rafs/src/builder/stargz.rs

@@ -20,7 +20,7 @@ use nydus_storage::{RAFS_MAX_CHUNKS_PER_BLOB, RAFS_MAX_CHUNK_SIZE};
 use nydus_utils::compact::makedev;
 use nydus_utils::compress::{self, compute_compressed_gzip_size};
 use nydus_utils::digest::{self, DigestData, RafsDigest};
-use nydus_utils::{root_tracer, timing_tracer, try_round_up_4k, ByteSize};
+use nydus_utils::{lazy_drop, root_tracer, timing_tracer, try_round_up_4k, ByteSize};
 use serde::{Deserialize, Serialize};
 
 use super::core::blob::Blob;
@@ -897,6 +897,8 @@ impl Builder for StargzBuilder {
             )?;
         }
 
+        lazy_drop(bootstrap_ctx);
+
         BuildOutput::new(blob_mgr, &bootstrap_mgr.bootstrap_storage)
     }
 }

rafs/src/builder/tarball.rs

@@ -32,7 +32,7 @@ use nydus_utils::compact::makedev;
 use nydus_utils::compress::zlib_random::{ZranReader, ZRAN_READER_BUF_SIZE};
 use nydus_utils::compress::ZlibDecoder;
 use nydus_utils::digest::RafsDigest;
-use nydus_utils::{div_round_up, root_tracer, timing_tracer, BufReaderInfo, ByteSize};
+use nydus_utils::{div_round_up, lazy_drop, root_tracer, timing_tracer, BufReaderInfo, ByteSize};
 
 use super::core::blob::Blob;
 use super::core::context::{
@@ -585,6 +585,8 @@ impl Builder for TarballBuilder {
             )?;
         }
 
+        lazy_drop(bootstrap_ctx);
+
         BuildOutput::new(blob_mgr, &bootstrap_mgr.bootstrap_storage)
     }
 }

src/bin/nydus-image/main.rs

@@ -39,7 +39,9 @@ use nydus_storage::factory::BlobFactory;
 use nydus_storage::meta::{format_blob_features, BatchContextGenerator};
 use nydus_storage::{RAFS_DEFAULT_CHUNK_SIZE, RAFS_MAX_CHUNK_SIZE};
 use nydus_utils::trace::{EventTracerClass, TimingTracerClass, TraceClass};
-use nydus_utils::{compress, digest, event_tracer, register_tracer, root_tracer, timing_tracer};
+use nydus_utils::{
+    compress, digest, event_tracer, lazy_drop, register_tracer, root_tracer, timing_tracer,
+};
 use serde::{Deserialize, Serialize};
 
 use crate::unpack::{OCIUnpacker, Unpacker};
@@ -1026,6 +1028,8 @@ impl Command {
             "total_build"
         )?;
 
+        lazy_drop(build_ctx);
+
         // Some operations like listing xattr pairs of certain namespace need the process
         // to be privileged. Therefore, trace what euid and egid are.
         event_tracer!("euid", "{}", geteuid());

utils/src/lib.rs

@@ -110,6 +110,21 @@ impl Delayer {
     }
 }
 
+struct LazyDrop<T> {
+    v: T,
+}
+
+unsafe impl<T> Send for LazyDrop<T> {}
+
+/// Lazy drop of object.
+pub fn lazy_drop<T: 'static>(v: T) {
+    let v = LazyDrop { v };
+    std::thread::spawn(move || {
+        std::thread::sleep(Duration::from_secs(600));
+        let _ = v.v;
+    });
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;