From 6a679ffc8125419123e416fbeb14a4e118e9f366 Mon Sep 17 00:00:00 2001 From: The8472 Date: Sat, 13 Feb 2021 00:54:17 +0100 Subject: [PATCH] bypass auto_da_alloc for metadata files --- compiler/rustc_interface/src/passes.rs | 2 +- compiler/rustc_interface/src/util.rs | 18 ++++++++++++++++++ 2 files changed, 19 insertions(+), 1 deletion(-) diff --git a/compiler/rustc_interface/src/passes.rs b/compiler/rustc_interface/src/passes.rs index 56aa3939b22dc..c1ae450483e67 100644 --- a/compiler/rustc_interface/src/passes.rs +++ b/compiler/rustc_interface/src/passes.rs @@ -983,7 +983,7 @@ fn encode_and_write_metadata( .unwrap_or_else(|err| tcx.sess.fatal(&format!("couldn't create a temp dir: {}", err))); let metadata_tmpdir = MaybeTempDir::new(metadata_tmpdir, tcx.sess.opts.cg.save_temps); let metadata_filename = emit_metadata(tcx.sess, &metadata, &metadata_tmpdir); - if let Err(e) = fs::rename(&metadata_filename, &out_filename) { + if let Err(e) = util::non_durable_rename(&metadata_filename, &out_filename) { tcx.sess.fatal(&format!("failed to write {}: {}", out_filename.display(), e)); } if tcx.sess.opts.json_artifact_notifications { diff --git a/compiler/rustc_interface/src/util.rs b/compiler/rustc_interface/src/util.rs index b7dc539c6d606..dc2c90472c0ee 100644 --- a/compiler/rustc_interface/src/util.rs +++ b/compiler/rustc_interface/src/util.rs @@ -670,6 +670,24 @@ pub fn build_output_filenames( } } +#[cfg(not(target_os = "linux"))] +pub fn non_durable_rename(src: &Path, dst: &Path) -> std::io::Result<()> { + std::fs::rename(src, dst) +} + +/// This function attempts to bypass the auto_da_alloc heuristic implemented by some filesystems +/// such as btrfs and ext4. When renaming over a file that already exists then they will "helpfully" +/// write back the source file before committing the rename in case a developer forgot some of +/// the fsyncs in the open/write/fsync(file)/rename/fsync(dir) dance for atomic file updates. +/// +/// To avoid triggering this heuristic we delete the destination first, if it exists. +/// The cost of an extra syscall is much lower than getting descheduled for the sync IO. +#[cfg(target_os = "linux")] +pub fn non_durable_rename(src: &Path, dst: &Path) -> std::io::Result<()> { + let _ = std::fs::remove_file(dst); + std::fs::rename(src, dst) +} + // Note: Also used by librustdoc, see PR #43348. Consider moving this struct elsewhere. // // FIXME: Currently the `everybody_loops` transformation is not applied to: