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Ayush RanjanandgVisor bot
f8e29b59d7
This is an optimization that will prevent needless lookups on lower layers for
directories. This is analogous to the Linux commit 97c684cc9110 ("ovl: create
directories inside merged parent opaque").
If mkdir(2) does succeed, then none of the lower layers have a file at that
position, otherwise mkdir(2) would have failed with EEXIST.
Changes on the lower layer underneath a new upper layer directory are not
visible. See the following for example:
```
$ sudo mount -t overlay -o lowerdir=lower,upperdir=upper,workdir=workdir none overlay
$ mkdir -p overlay/dir/dir1
$ mkdir -p lower/dir/dir2
$ ls overlay/dir/
dir1
```
Benchmarking shows that this change cuts ABSL build time by 9.5%!
```
goos: linux
goarch: amd64
cpu: Intel(R) Xeon(R) CPU @ 2.20GHz
│ /tmp/benchout.runsc │ /tmp/benchout.runsc-opt │
│ sec/op │ sec/op vs base │
BuildABSL/page_cache.clean/filesystem.bindfs-8 71.16 ± 12% 64.40 ± 3% -9.50% (p=0.003 n=8)
BuildGRPC/page_cache.clean/filesystem.bindfs-8 418.2 ± 1% 419.9 ± 1% ~ (p=0.721 n=8)
RubySpecTest/page_cache.clean/filesystem.bindfs-8 76.67 ± 5% 75.17 ± 1% ~ (p=0.382 n=8)
geomean 131.6 126.7 -3.78%
│ /tmp/benchout.runsc │ /tmp/benchout.runsc-opt │
│ load.sec │ load.sec vs base │
RubySpecTest/page_cache.clean/filesystem.bindfs-8 12.95 ± 6% 12.80 ± 5% ~ (p=0.625 n=8)
```
PiperOrigin-RevId: 538823897