The scrollback-limit setting doesn't take effect no matter how small I set its value

[cos4ni2s]

Issue Description

I can't limit the number of lines I can scroll-back to no matter how small I set the value of the scrollback-limit setting at.

Expected Behavior

Scroll-back is limited to the set value.

Actual Behavior

Scroll-back isn't limiter no matter how small I set its value.

Reproduction Steps

1. Open Ghostty.
2. Execute a command that returns too many lines.
3. Scroll-back and see.

Ghostty Logs

No response

Ghostty Version

Ghostty 1.2.3-arch2.1

Version
  - version: 1.2.3-arch2.1
  - channel: tip
Build Config
  - Zig version   : 0.14.1
  - build mode    : builtin.OptimizeMode.ReleaseFast
  - app runtime   : apprt.Runtime.gtk
  - font engine   : font.main.Backend.fontconfig_freetype
  - renderer      : renderer.generic.Renderer(renderer.OpenGL)
  - libxev        : io_uring
  - kernel version: 6.18.2-2-cachyos
  - desktop env   : other
  - GTK version   :
    build         : 4.20.2
    runtime       : 4.20.3
  - libadwaita    : enabled
    build         : 1.8.1
    runtime       : 1.8.2
  - libX11        : enabled
  - libwayland    : enabled

OS Version Information

CachyOS

(Linux only) Display Server

Wayland

(Linux only) Desktop Environment/Window Manager

KDE Plasma 6.5.4

Minimal Ghostty Configuration

scrollback-limit = 8

Additional Relevant Configuration

No response

I acknowledge that:

• I have reviewed the FAQ and confirm that my issue is NOT among them.
• I have searched the Ghostty repository (both open and closed Discussions and Issues) and confirm this is not a duplicate of an existing issue or discussion.
• I have checked the "Preview" tab on all text fields to ensure that everything looks right, and have wrapped all configuration and code in code blocks with a group of three backticks (```) on separate lines.

[danielwe]

This is an implementation artifact. The actual scrollback won't ever be exactly zero, because Ghostty needs some extra working memory in addition to the current viewport, and for performance, the size of this workspace is rounded up to align with hardware memory page boundaries. Ghostty will let you scroll the contents of this workspace, because hiding parts of it from you to exactly match what you see with your scrollback-limit config would complicate the implementation for no clear benefit.

There's some brief explanation/discussion in various comments around the codebase, such as here:

ghostty/src/terminal/PageList.zig

Lines 216 to 219 in 73a93ab

	/// Returns the minimum valid "max size" for a given number of rows and cols
	/// such that we can fit the active area AND at least two pages. Note we
	/// need the two pages for algorithms to work properly (such as grow) but
	/// we don't need to fit double the active area.

. This behavior is also implied (though perhaps a bit opaquely) by the following line in the docs:

No matter what this is set to, enough memory will always be allocated for the visible screen and anything leftover is the limit for the scrollback. (https://ghostty.org/docs/config/reference#scrollback-limit)

So, in short, if you set scrollback-limit = 0, Ghostty will allocate the minimum amount of memory required and you'll get the shortest possible scrollback, but it won't actually be zero. More generally, your scrollback-limit config is rounded up to the nearest page size.

[cos4ni2s]

I usually limit the scroll-back in every terminal I use. A practical benefit of limiting the scroll-back size is consuming less memory, another one is to think twice before executing a command.

[danielwe]

A practical benefit of limiting the scroll-back size is consuming less memory

Setting scrollback-limit = 0 guarantees that Ghostty will use as little memory as possible.

[cos4ni2s]

Thank you!
I would like to point out that setting scrollback-limit = 0 limits the scroll-back to the visible screen (as documented) but setting it to scrollback-limit = 1 or any other value bigger than zero doesn't limit it at all.

[danielwe]

I would like to point out that setting scrollback-limit = 0 limits the scroll-back to the visible screen

Ah, you're right, there is indeed a special case for this:

ghostty/src/terminal/Screen.zig

Line 262 in df8dde9

.no_scrollback = opts.max_scrollback == 0,

Do note that this doesn't actually save you any memory compared to scrollback_limit = 1. It just disables scrolling. The minimum amount of page list memory is still allocated.

setting it to scrollback-limit = 1 or any other value bigger than zero doesn't limit it at all.

As I've explained above, it does limit the scrollback to the minimum possible size. It's just that the minimum is significantly larger than 1 byte. Try running seq 10000 and scrolling back. You'll notice that with scrollback-limit = 1, you can only scroll a few hundred lines, maybe up to a thousand (exact number depending on the size of your terminal and your OS/architecture). With the default config you can scroll several thousand lines (I observe between 8000 and 9000, but again, it depends on the size of your terminal).

[marcelovital]

I have the same issue here. No matter how I set it up, absolutely no change, and that's a deal breaker which forces to move away from Ghostty. Any idea on the cause?

[danielwe]

The other comment thread with the marked answer explains how the scrollback-limit setting works. What specifically are you trying and failing to accomplish?

[marcelovital]

Sorry, never mind. Apparently I have an issue with Ghostty reloading the config, even after cmd+shift+, AND quitting the application and opening it again. I could only see the config change the following day (probably because of a computer restart).
Just happened today with other settings, such as window-width, which didn't get reloaded even after an application restart.
Thanks for the help, anyway!