This adds another +4 bytes* to Link nodes, but allows for the in-memory
tree to be properly exported to JSON, which we'll need for multithreaded
export. It's also slightly nicer conceptually, as we can now detect
inconsistencies without throwing away the actual data, so have a better
chance of recovering on partial refresh. Still unlikely, anyway, but
whatever.
(* but saves 4+ bytes per unique inode in the inode map, so the memory
increase is only noticeable when links are repeated in the scanned tree.
Admittedly, that may be the common case)
Ended up turning the Links into a doubly-linked list, because the
current approach of refreshing a subdirectory makes it more likely to
run into problems with the O(n) removal behavior of singly-linked lists.
Also found a bug that was present in the old scanning code as well;
fixed here and in c41467f240.
Benchmarks are looking very promising this time. This commit breaks a
lot, though:
- Hard link counting
- Refreshing
- JSON import
- JSON export
- Progress UI
- OOM handling is not thread-safe
All of which needs to be reimplemented and fixed again. Also haven't
really tested this code very well yet so there's likely to be bugs.
There's also a behavioral change: --exclude-kernfs is not checked on the
given root directory anymore, meaning that the filesystem the user asked
to scan is being scanned even if that's a 'kernfs'. I suspect that's
more sensible behavior.
The old scan.zig was quite messy and hard for me to reason about and
extend, this new sink API is looking to be less confusing. I hope it
stays that way as more features are added.
Fixes these errors (introduced in https://github.com/ziglang/zig/pull/18017
and 6b1a823b2b ):
```
src/main.zig:290:13: error: local variable is never mutated
var line_ = line_fbs.getWritten();
^~~~~
src/main.zig:290:13: note: consider using 'const'
src/main.zig:450:17: error: local variable is never mutated
var path = std.fs.path.joinZ(allocator, &.{p, "ncdu", "config"}) catch unreachable;
^~~~
src/main.zig:450:17: note: consider using 'const'
...
```
Will be included in future Zig 0.12, this fix is backward compatible:
ncdu still builds and runs fine on Zig 0.11.0.
Signed-off-by: Eric Joldasov <bratishkaerik@getgoogleoff.me>
Still using a few embedded packed structs for those fields that benefit
from bit packing. This isn't much cleaner than using packed structs for
everything, but it does have better semantics. In particular, all fields
(except those inside nested packed structs) are now guaranteed to be
byte-aligned and I don't have to worry about the memory representation
of integers when pointer-casting between the different Entry types.
As aluded to in the previous commit. This approach keeps track of hard
links information much the same way as ncdu 1.16, with the main
difference being that the actual /counting/ of hard link sizes is
deferred until the scan is complete, thus allowing the use of a more
efficient algorithm and amortizing the counting costs.
As an additional benefit, the links listing in the information window
now doesn't need a full scan through the in-memory tree anymore.
A few memory usage benchmarks:
1.16 2.0-beta1 this commit
root: 429 162 164
backup: 3969 1686 1601
many links: 155 194 106
many links2*: 155 602 106
(I'm surprised my backup dir had enough hard links for this to be an
improvement)
(* this is the same as the "many links" benchmarks, but with a few
parent directories added to increase the tree depth. 2.0-beta1 doesn't
like that at all)
Performance-wise, refresh and delete operations can still be improved a
bit.
While this simplifies the code a bit, it's a regression in the sense
that it increases memory use.
This commit is yak shaving for another hard link counting approach I'd
like to try out, which should be a *LOT* less memory hungry compared to
the current approach. Even though it does, indeed, add an extra cost of
these parent node pointers.
This complicated the scan code more than I had anticipated and has a
few inherent bugs with respect to calculating shared hardlink sizes.
Still, the merge approach avoids creating a full copy of the subtree, so
that's another memory usage related win compared to the C version.
On the other hand, it does leak memory if nodes can't be reused.
Not quite as well tested as I should have, so I'm sure there's bugs.
Two differences compared to the C version:
- You can now select individual paths in the listing, pressing enter
will open the selected path in the browser window.
- Creating this listing is much slower and requires, in the worst case,
a full traversal through the in-memory tree. I've tested this without
the same-dev and shared-parent optimizations (i.e. worst case) on an
import with 30M files and performance was still quite acceptable - the
listing completed in a second - so I didn't bother adding a loading
indicator. On slower systems and even larger trees this may be a
little annoying, though.
(also, calling nonl() apparently breaks detection of the return key,
neither \n nor KEY_ENTER are emitted for some reason)
I had used them as a HashSet with mutable keys already in order to avoid
padding problems. This is not always necessary anymore now that Zig's
new HashMap uses separate arrays for keys and values, but I still need
the HashSet trick for the link_count nodes table, as the key itself
would otherwise have padding.
Under the assumption that there are no external references to files
mentioned in the dump, i.e. a file's nlink count matches the number of
times the file occurs in the dump.
This machinery could also be used for regular scans, when you want to
scan an individual directory without caring about external hard links.
Maybe that should be the default, even? Not sure...
In a similar way to the C version of ncdu: by wrapping malloc(). It's
simpler to handle allocation failures at the source to allow for easy
retries, pushing the retries up the stack will complicate code somewhat
more. Likewise, this is a best-effort approach to handling OOM,
allocation failures in ncurses aren't handled and display glitches may
occur when we get an OOM inside a drawing function.
This is a somewhat un-Zig-like way of handling errors and adds
scary-looking 'catch unreachable's all over the code, but that's okay.
Performance is looking great, but the code is rather ugly and
potentially buggy. Also doesn't handle hard links without an "nlink"
field yet.
Error handling of the import code is different from what I've been doing
until now. That's intentional, I'll change error handling of other
pieces to call ui.die() directly rather than propagating error enums.
The approach is less testable but conceptually simpler, it's perfectly
fine for a tiny application like ncdu.
I plan to add more display options, but ran out of keys to bind.
Probably going for a quick-select menu thingy so that we can keep the
old key bindings for people accustomed to it.
The graph width algorithm is slightly different, but I think this one's
a minor improvement.
I initially wanted to keep a directory's block count and size as a
separate field so that exporting an in-memory tree to a JSON dump would
be easier to do, but that doesn't seem like a common operation to
optimize for. We'll probably need the algorithms to subtract sub-items
from directory counts anyway, so such an export can still be
implemented, albeit slower.
The new data model is supposed to solve a few problems with ncdu 1.x's
'struct dir':
- Reduce memory overhead,
- Fix extremely slow counting of hard links in some scenarios
(issue #121)
- Add support for counting 'shared' data with other directories
(issue #36)
Quick memory usage comparison of my root directory with ~3.5 million
files (normal / extended mode):
ncdu 1.15.1: 379M / 451M
new (unaligned): 145M / 178M
new (aligned): 155M / 200M
There's still a /lot/ of to-do's left before this is usable, however,
and there's a bunch of issues I haven't really decided on yet, such as
which TUI library to use.
Backporting this data model to the C version of ncdu is also possible,
but somewhat painful. Let's first see how far I get with Zig.
