dirstate-tree: Skip readdir() in `hg status -mard`
When running the status algorithm in a mode where we don’t list unknown
or ignored files, all we care about are files that are listed in the dirstate.
We can there for skip making expensive calls to readdir() to list the contents
of filesystem directories, and instead only run stat() to get the filesystem
state of files listed in the dirstate. (This state may be an error for files
that don’t exist anymore on the filesystem.)
On 16 CPU threads, this reduces the time spent in the `status()` function for
`hg status -mard` on an old snapshot of mozilla-central from ~70ms to ~50ms.
Differential Revision: https://phab.mercurial-scm.org/D10752
$ hg init repo
$ cd repo
$ touch a.html b.html c.py d.py
$ cat > frontend.sparse << EOF
> [include]
> *.html
> EOF
$ hg -q commit -A -m initial
$ echo 1 > a.html
$ echo 1 > c.py
$ hg commit -m 'commit 1'
Enable sparse profile
$ cat .hg/requires
dotencode
exp-dirstate-v2 (dirstate-v2 !)
fncache
generaldelta
persistent-nodemap (rust !)
revlog-compression-zstd (zstd !)
revlogv1
sparserevlog
store
testonly-simplestore (reposimplestore !)
$ hg debugsparse --config extensions.sparse= --enable-profile frontend.sparse
$ ls -A
.hg
a.html
b.html
Requirement for sparse added when sparse is enabled
$ cat .hg/requires
dotencode
exp-dirstate-v2 (dirstate-v2 !)
exp-sparse
fncache
generaldelta
persistent-nodemap (rust !)
revlog-compression-zstd (zstd !)
revlogv1
sparserevlog
store
testonly-simplestore (reposimplestore !)
Client without sparse enabled reacts properly
$ hg files
abort: repository is using sparse feature but sparse is not enabled; enable the "sparse" extensions to access
[255]
Requirement for sparse is removed when sparse is disabled
$ hg debugsparse --reset --config extensions.sparse=
$ cat .hg/requires
dotencode
exp-dirstate-v2 (dirstate-v2 !)
fncache
generaldelta
persistent-nodemap (rust !)
revlog-compression-zstd (zstd !)
revlogv1
sparserevlog
store
testonly-simplestore (reposimplestore !)
And client without sparse can access
$ hg files
a.html
b.html
c.py
d.py
frontend.sparse