macos: hide /nix from Finder and stop fseventsd journaling#183
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macos: hide /nix from Finder and stop fseventsd journaling#183
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Mic92
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Apr 14, 2026
| tracing::warn!(?err, path = %metadata_never_index.display(), "Could not remove Spotlight opt-out marker"); | ||
| } | ||
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| let no_log = self.mount_point.join(".fseventsd").join("no_log"); |
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I have to do a bit of research if there is anything that will stop working if we do this.
On a mature Nix store (>500k entries), Finder and the system open/save
panel XPC service (com.apple.appkit.xpc.openAndSavePanelService) walk the
/nix synthetic firmlink whenever the user browses near / and cache one
_FileCache + NSURL object per store entry inside DesktopServicesPriv.
On a 700k-entry store this leaks ~950 MB RSS in Finder and ~900 MB in the
open-panel service, plus ~50% CPU re-syncing TNode::SynchronizeChildren ->
getattrlistbulk on every fsevent. The existing fstab nobrowse option hides
the *volume* from the sidebar and from Spotlight/mds, but not the firmlink
directory entry under / that DesktopServices enumerates.
Add a SuppressVolumeIndexing action that, on the mounted /nix volume:
- runs chflags hidden /nix (UF_HIDDEN on the volume root inode hides
the firmlink from Finder/NSOpenPanel
directory listings; persists across
remounts)
- drops .fseventsd/no_log (Apple-documented per-volume fseventsd
journal opt-out; cuts write I/O during
builds and GC)
Spotlight needs no extra marker: nobrowse already opts the volume out, and
.metadata_never_index is undocumented and unreliable on recent macOS.
Wire it into CreateNixVolume after enable_ownership, when the volume is
mounted and owned. Revert is best-effort since uninstall removes the
volume anyway.
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Description
On a mature Nix store (>500k entries), Finder and the system open/save panel
XPC service (
com.apple.appkit.xpc.openAndSavePanelService) walk the/nixsynthetic firmlink whenever the user browses near
/and cache one_FileCache+NSURLobject per store entry insideDesktopServicesPriv.On a 700k-entry store this leaks ~950 MB RSS in Finder and ~900 MB in the
open-panel service, plus ~50 % CPU re-syncing
TNode::SynchronizeChildren → getattrlistbulkon every fsevent. The existingfstab
nobrowseoption hides the volume from the sidebar (and fromSpotlight/mds), but not the firmlink directory entry under
/thatDesktopServices enumerates.
Adds a
SuppressVolumeIndexingaction that, on the mounted/nixvolume:chflags hidden /nix— setsUF_HIDDENon the volume root inode soFinder/NSOpenPanel skip the firmlink in directory listings; flag persists
across remounts. This is the load-bearing fix for the RSS leak.
/nix/.fseventsd/no_log— Apple-documented per-volume fseventsdjournal opt-out
(FSEvents Programming Guide); cuts write I/O during builds and
GC.
Spotlight needs no extra marker:
nobrowse(MNT_DONTBROWSE) already optsthe volume out of mds, and
.metadata_never_indexis undocumented andreported unreliable on recent macOS, so it is intentionally not written.
Wired into
CreateNixVolumeafterenable_ownership(volume mounted andowned). Revert is best-effort since uninstall removes the volume anyway.
Evidence (heap / sample on a 700k-entry store)
Object count tracks
ls /nix/store | wc -l. Same signature inopenAndSavePanelService.Checklist
tests/fixtures/macos/macos.json