Re: Some rough edges of core.fsmonitor
- From
Ben Peart <peartben@gmail.com>
- Date
- Jan 30, 2018, 01:21 UTC
- Message-ID
- <56b8d8a3-9483-330d-64a4-ec0295b254ac@gmail.com>
- In-Reply-To
- <CACBZZX74WcK4qX5O1E_6nxv7f4Vpns3O-7dcURbs+QneKsA87Q@mail.gmail.com>
On 1/28/2018 5:28 PM, Ævar Arnfjörð Bjarmason wrote:
Show 49 quoted lines
> On Sun, Jan 28, 2018 at 9:44 PM, Johannes Schindelin
> <Johannes.Schindelin@gmx.de> wrote:
>> Hi,
>>
>> On Sat, 27 Jan 2018, Ævar Arnfjörð Bjarmason wrote:
>>
>>> I just got around to testing this since it landed, for context some
>>> previous poking of mine in [1].
>>>
>>> Issues / stuff I've noticed:
>>>
>>> 1) We end up invalidating the untracked cache because stuff in .git/
>>> changed. For example:
>>>
>>> 01:09:24.975524 fsmonitor.c:173 fsmonitor process '.git/hooks/fsmonitor-watchman' returned success
>>> 01:09:24.975548 fsmonitor.c:138 fsmonitor_refresh_callback '.git'
>>> 01:09:24.975556 fsmonitor.c:138 fsmonitor_refresh_callback '.git/config'
>>> 01:09:24.975568 fsmonitor.c:138 fsmonitor_refresh_callback '.git/index'
>>> 01:09:25.122726 fsmonitor.c:91 write fsmonitor extension successful
>>>
>>> Am I missing something or should we do something like:
>>>
>>> diff --git a/fsmonitor.c b/fsmonitor.c
>>> index 0af7c4edba..5067b89bda 100644
>>> --- a/fsmonitor.c
>>> +++ b/fsmonitor.c
>>> @@ -118,7 +118,12 @@ static int query_fsmonitor(int version, uint64_t last_update, struct strbuf *que
>>>
>>> static void fsmonitor_refresh_callback(struct index_state *istate, const char *name)
>>> {
>>> - int pos = index_name_pos(istate, name, strlen(name));
>>> + int pos;
>>> +
>>> + if (!strcmp(name, ".git") || starts_with(name, ".git/"))
>>> + return;
>>> +
>>> + pos = index_name_pos(istate, name, strlen(name));
>>
>> I would much rather have the fsmonitor hook already exclude those.
>
> As documented the fsmonitor-watchman hook we ship doesn't work as
> described in githooks(5), unless "files in the working directory" is
> taken to include .git/, but I haven't seen that ever used.
>
> On the other hand relying on arbitrary user-provided hooks to do the
> right thing at the cost of silent performance degradation is bad. If
> we're going to expect the hook to remove these we should probably
> warn/die here if it does send us .git/* files.
> I'm not sure how often something is modified in the git directory when nothing was modified in the working directory but this seems like a nice optimization.
We can't just blindly ignore changes under ".git" as the git directory may have been moved somewhere else. Instead we'd need to use get_git_dir().
Rather than assuming the hook will optimize for this particular case, I think a better solution would be to update untracked_cache_invalidate_path() so that it doesn't invalidate the untracked cache and mark the index as dirty when it was asked to invalidate a path under GIT_DIR. I can't think of a case when that would be the desired behavior.
Somewhat off topic but related to the overall performance discussion: I've also thought the untracked cache shouldn't mark the index as dirty except in the case where the extension is being added or removed. We've observed that it causes unnecessary index writes that actually slows down overall performance.
Since it is a cache, it does not require the index to be written out for correctness, it can simply update the cache again the next time it is needed. This is typically faster than the cost of the index write so makes things faster overall. I adopted this same model with the fsmonitor extension.
Show 5 quoted lines
>> If you *must* add these comparisons, you have to use fspathcmp() and >> fspathncmp() instead (because case-insensitivity). > > Thanks. >