This reduces allocations, in number and in size, while getting extended
attributes. This is mostly noticable when there is a large number of new
files to scan and we're running with the default scanProgressInterval --
then a queue of files is built in-memory, and this queue includes
extended attributes as part of file metadata. (Arguable it shouldn't,
but that's a more difficult and involved change.)
With 1M files to scan, each with one extended attribute, current peak
memory usage looks like this:
Showing nodes accounting for 1425.30MB, 98.19% of 1451.64MB total
Dropped 1435 nodes (cum <= 7.26MB)
Showing top 10 nodes out of 54
flat flat% sum% cum cum%
976.56MB 67.27% 67.27% 976.56MB 67.27%
github.com/syncthing/syncthing/lib/fs.getXattr
305.44MB 21.04% 88.31% 305.44MB 21.04%
github.com/syncthing/syncthing/lib/scanner.(*walker).walk.func1
45.78MB 3.15% 91.47% 1045.23MB 72.00%
github.com/syncthing/syncthing/lib/fs.(*BasicFilesystem).GetXattr
22.89MB 1.58% 93.04% 22.89MB 1.58%
github.com/syncthing/syncthing/lib/fs.listXattr
22.89MB 1.58% 94.62% 22.89MB 1.58%
github.com/syncthing/syncthing/lib/protocol.(*PlatformData).SetXattrs
16MB 1.10% 95.72% 16.01MB 1.10%
github.com/syndtr/goleveldb/leveldb/memdb.New
After the change, it's this:
Showing nodes accounting for 502.32MB, 95.70% of 524.88MB total
Dropped 1400 nodes (cum <= 2.62MB)
Showing top 10 nodes out of 91
flat flat% sum% cum cum%
305.43MB 58.19% 58.19% 305.43MB 58.19%
github.com/syncthing/syncthing/lib/scanner.(*walker).walk.func1
45.79MB 8.72% 66.91% 68.68MB 13.09%
github.com/syncthing/syncthing/lib/fs.(*BasicFilesystem).GetXattr
32MB 6.10% 73.01% 32.01MB 6.10%
github.com/syndtr/goleveldb/leveldb/memdb.New
22.89MB 4.36% 77.37% 22.89MB 4.36%
github.com/syncthing/syncthing/lib/fs.listXattr
22.89MB 4.36% 81.73% 22.89MB 4.36%
github.com/syncthing/syncthing/lib/protocol.(*PlatformData).SetXattrs
15.35MB 2.92% 84.66% 15.36MB 2.93%
github.com/syndtr/goleveldb/leveldb/util.(*BufferPool).Get
15.28MB 2.91% 87.57% 15.28MB 2.91% strings.(*Builder).grow
(The usage for xattrs is reduced from 976 MB to 68 MB)
This adds support for syncing extended attributes on supported
filesystem on Linux, macOS, FreeBSD and NetBSD. Windows is currently
excluded because the APIs seem onerous and annoying and frankly the uses
cases seem few and far between. On Unixes this also covers ACLs as those
are stored as extended attributes.
Similar to ownership syncing this will optional & opt-in, which two
settings controlling the main behavior: one to "sync" xattrs (read &
write) and another one to "scan" xattrs (only read them so other devices
can "sync" them, but not apply any locally).
Co-authored-by: Tomasz Wilczyński <twilczynski@naver.com>
