[thin_check (rust)] Use vec::with_capacity() to avoid reallocations.

src/io_engine.rs

@@ -80,7 +80,7 @@ impl SyncIoEngine {
     }
 
     pub fn new(path: &Path, nr_files: usize, writeable: bool) -> Result<SyncIoEngine> {
-        let mut files = Vec::new();
+        let mut files = Vec::with_capacity(nr_files);
         for _n in 0..nr_files {
             files.push(SyncIoEngine::open_file(path, writeable)?);
         }

src/pdata/btree.rs

@@ -199,7 +199,7 @@ impl BTreeWalker {
         NV: NodeVisitor<V>,
         V: Unpack,
     {
-        let mut blocks = Vec::new();
+        let mut blocks = Vec::with_capacity(bs.len());
         for b in bs {
             if self.sm_inc(*b)? == 0 {
                 blocks.push(Block::new(*b));

src/pdata/space_map.rs

@@ -159,8 +159,8 @@ impl Unpack for Bitmap {
     fn unpack(data: &[u8]) -> IResult<&[u8], Self> {
         let (mut i, header) = BitmapHeader::unpack(data)?;
 
-        let mut entries = Vec::new();
         let nr_words = (BLOCK_SIZE - BitmapHeader::disk_size() as usize) / 8;
+        let mut entries = Vec::with_capacity(nr_words * 32);
         for _w in 0..nr_words {
             let (tmp, mut word) = le_u64(i)?;
 

src/thin/check.rs

@@ -172,7 +172,7 @@ fn check_space_map(
         w.walk(&mut v, root.ref_count_root)?;
     }
 
-    let mut blocks = Vec::new();
+    let mut blocks = Vec::with_capacity(entries.len());
     for i in &entries {
         blocks.push(Block::new(i.blocknr));
     }
@@ -243,7 +243,7 @@ fn repair_space_map(ctx: &Context, entries: Vec<BitmapLeak>, sm: ASpaceMap) -> R
 
     let sm = sm.lock().unwrap();
 
-    let mut blocks = Vec::new();
+    let mut blocks = Vec::with_capacity(entries.len());
     for i in &entries {
         blocks.push(Block::new(i.loc));
     }