Re: [PATCH v3 00/34] Builtin FSMonitor Feature

On 7/1/21 1:40 PM, Ævar Arnfjörð Bjarmason wrote:

On Thu, Jul 01 2021, Jeff Hostetler via GitGitGadget wrote:

quoted

Here is V3 of my patch series to add a builtin FSMonitor daemon to Git. I
rebased this series onto v2.32.0.

V3 addresses most of the previous review comments and things we've learned
from our experimental testing of V2. (A version of V2 was shipped as an
experimental feature in the v2.32.0-based releases of Git for Windows and
VFS for Git.)

There are still a few items that I need to address, but that list is getting
very short.

...

quoted

   fsmonitor-fs-listen-win32: stub in backend for Windows
   fsmonitor-fs-listen-macos: stub in backend for MacOS

I left some light comments on the repo-settings.c part of this to follow
up from a previous round.

Thanks.

Any other testing of it is stalled by there being no linux backend for
it as part of this series. I see from spelunking repos that Johannes had
a WIP compat/fsmonitor/linux.c which looks like it could/should mostly
work, but the API names all changed since then, and after a short try I
gave up on trying to rebase it.

The early Linux version was dropped because inotify does not give
recursive coverage -- only the requested directory.  Using inotify
requires adding a watch to each subdirectory (recursively) in the
worktree.  There's a system limit on the maximum number of watched
directories (defaults to 8K IIRC) and that limit is system-wide.

Since the whole point was to support large very large repos, using
inotify was a non-starter, so I removed the Linux version from our
patch series.  For example, the first repo I tried it on (outside
of the test suite) had 25K subdirectories.

I'm told there is a new fanotify API in recent Linux kernels that
is a better fit for what we need, but we haven't had time to investigate
it yet.

I'd really prefer for git not to have features that place free platforms
at a disadvantage against proprietary platforms if it can be avoided,
and in this case the lack of a Linux backend also means much less
widespread testing of the feature among the development community / CI.

This feature is always going to have platform-specific components,
so the lack of one platform or another should not stop us from
discussing it for the platforms that can be supported.

And given the size and complexity of the platform-specific code,
we should not assume that "just test it on Linux" is sufficient.
Yes, there are some common/shared routines/data structures in the
daemon, but hard/tricky parts are in the platform layer.

Jeff