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From:   Junio C Hamano <gitster@pobox.com>
To:     Taylor Blau <me@ttaylorr.com>
Cc:     Nipunn Koorapati <nipunn1313@gmail.com>,
        Alex Vandiver via GitGitGadget <gitgitgadget@gmail.com>,
        git@vger.kernel.org, Derrick Stolee <stolee@gmail.com>,
        Utsav Shah <utsav@dropbox.com>,
        Alex Vandiver <alexmv@dropbox.com>
Subject: Re: [PATCH 1/4] fsmonitor: use fsmonitor data in `git diff`
References: <pull.756.git.1602968677.gitgitgadget@gmail.com>
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        <20201018041642.GB2262492@nand.local>
        <xmqq1rhw86ur.fsf@gitster.c.googlers.com>
        <20201018234344.GC4204@nand.local>
Date:   Mon, 19 Oct 2020 10:23:26 -0700
In-Reply-To: <20201018234344.GC4204@nand.local> (Taylor Blau's message of
        "Sun, 18 Oct 2020 19:43:44 -0400")
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Taylor Blau <me@ttaylorr.com> writes:

>> > There is some overhead to invoke the hook and talk to watchman, but
>> > I'd expect that to be dwarfed by not having to issue O(# files)
>> > syscalls.
>>
>> "invoke the hook"---is that a pipe+fork+exec, or something else that
>> is far lighter-weight?
>
> The former; see 'fsmonitor.c:query_fsmonitor()'.

It brings us back to the "overhead of how many lstat(2) takes us
closer to the overhead of a single pipe+fork+exec plus reading from
the pipe", doesn't it?