An open's writes in a row to one place go in as one edit: a 10 MB body write is linear

Each body or data write copied and hashed the whole buffer, so a write the mount cut in 8 KB pieces was quadratic: 10 MB took 50 s and a 1 MB insert into 10 MB 11 s, holding the editor's turn. An open's appends to body, or inserts going on at data's address, are now held and put in as one splice (one copy, one undo step, one line-starts pass) before any other request, the close, or the editor's step once the writes pause 20 ms. fs.py-driven: 2 MB 2.19 -> 0.16 s, 10 MB 50.17 -> 0.78 s, 1 MB data into 10 MB 11.49 -> 0.26 s. A body-2m case (2 MB in 256 KB writes on one open) joins the perf gate: 84023 -> 15785 us; baselines re-recorded.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

1 files changed, 20 insertions, 0 deletions

diff --git a/test/perf.zig b/test/perf.zig
index e244091c..c639178f 100644
--- a/test/perf.zig
+++ b/test/perf.zig
@@ -46,6 +46,9 @@ const Op = enum {
     page_down,
     wheel,
     edit_char,
+    /// 2 MB appended to the file through 9P, on one open, in 256 KB
+    /// writes: linear, not a copy of the whole buffer per write.
+    body_write,
 
     fn label(o: Op) []const u8 {
         return switch (o) {
@@ -56,10 +59,25 @@ const Op = enum {
             .page_down => "page-down",
             .wheel => "wheel",
             .edit_char => "edit-char",
+            .body_write => "body-2m",
         };
     }
 };
 
+var body_chunk: [256 * 1024]u8 = @splat('y');
+
+/// The body_write gesture: an open of the pane's body, eight 256 KB writes,
+/// a read (which the held writes go in before), the close.
+fn bodyWrite(core: *pardes.Pardes, serial: u32) void {
+    const Node = pardes.ctlfs.Node;
+    const body = Node.of(serial, .body);
+    for (&body_chunk, 0..) |*c, i| c.* = if (i % 64 == 63) '\n' else 'y';
+    const h = core.serveFs(.{ .tag = 1, .op = .open, .node = body, .omode = 1 }).handle;
+    for (0..8) |_| _ = core.serveFs(.{ .tag = 2, .op = .write, .node = body, .handle = h, .data = &body_chunk });
+    _ = core.serveFs(.{ .tag = 3, .op = .getattr, .node = body, .handle = h });
+    _ = core.serveFs(.{ .tag = 4, .op = .release, .node = body, .handle = h, .opened = true });
+}
+
 const TermFixture = struct {
     name: []const u8,
     kb: usize,
@@ -514,12 +532,14 @@ fn measure(op: Op, fx: Fixture, path: []const u8, expected_bytes: usize, reps: u
             .page_down => core.update(.{ .key = .{ .cp = pardes.Key.page_down } }),
             .wheel => core.update(.{ .mouse = .{ .button = .wheel_down, .kind = .press, .col = wheel_col, .row = wheel_row } }),
             .edit_char => core.update(.{ .key = .{ .cp = 'x', .text = "x" } }),
+            .body_write => bodyWrite(core, pane.serial),
         }
         pump(core);
         _ = try frame(core);
         const dt = nowNs() -| t0;
         switch (op) {
             .open => unreachable,
+            .body_write => if (pane.file.?.content.len != before.len + 8 * body_chunk.len) return error.BodyWriteWasNotAppended,
             .render => if (pane.body.cur_row != before.row or pane.body.cur_col != before.col or pane.file.?.content.len != before.len)
                 return error.RenderChangedDocument,
             .key_down => if (pane.body.cur_row != before.row + 1) return error.DownDidNotMove,