libfreemkv: increase DEFAULT_PIPELINE_DEPTH to 32 for smoother mux speed

src/io/pipeline.rs

@@ -49,13 +49,14 @@ use crate::error::Error;
 /// Empirically tuned for sweep and mux — both want enough slack that
 /// short consumer stalls don't immediately back up onto the producer,
 /// but not so much that a producer outpacing the consumer accumulates
-/// arbitrary buffered work. `4` matches the depth sweep has used
-/// since 0.17.11 (originally in `disc/sweep_pipeline.rs`, now in
-/// `disc/sweep.rs::SweepSink`). Patch should usually use
-/// [`WRITE_THROUGH_DEPTH`] (`1`) instead — write-through gives clean
-/// back-pressure between every read attempt and the matching write,
-/// which matters when the consumer is updating the mapfile in lockstep.
-pub const DEFAULT_PIPELINE_DEPTH: usize = 4;
+/// arbitrary buffered work. `16` matches the depth needed for UHD-scale
+/// mux where WritebackFile sync_file_range on NFS can stall the consumer;
+/// sweep uses [`DEFAULT_PIPELINE_DEPTH`] directly, mux should use this
+/// or deeper if ISO read is moved to a separate producer thread. Patch
+/// should usually use [`WRITE_THROUGH_DEPTH`] (`1`) instead — write-through
+/// gives clean back-pressure between every read attempt and the matching
+/// write, which matters when the consumer is updating the mapfile in lockstep.
+pub const DEFAULT_PIPELINE_DEPTH: usize = 32;
 
 /// Channel depth for write-through pipelines. Each `send` fully
 /// drains before the next can enqueue. Use this when the producer

src/io/writeback_file.rs

@@ -27,7 +27,7 @@ use std::path::Path;
 
 use super::writeback::WritebackPipeline;
 
-const CHUNK_BYTES: u64 = 32 * 1024 * 1024;
+const WRITEBACK_CHUNK_BYTES: u64 = 32 * 1024 * 1024;
 
 pub(crate) struct WritebackFile {
     file: File,
@@ -42,7 +42,7 @@ impl WritebackFile {
     /// or appended files).
     pub(crate) fn new(mut file: File) -> io::Result<Self> {
         let pos = file.stream_position()?;
-        let pipeline = WritebackPipeline::new(&file, pos, CHUNK_BYTES);
+        let pipeline = WritebackPipeline::new(&file, pos, WRITEBACK_CHUNK_BYTES);
         Ok(Self {
             file,
             pipeline,