Repeated calls to isfile to look for identical ji files in precompile causes high disk pressure

[KristofferC]

Running something like:

@eval Base begin
    const isfile_cnt = Dict{String, Int64}()
    function Base.Filesystem.isfile(st::StatStruct)
        if haskey(isfile_cnt, st.desc)
            isfile_cnt[st.desc] += 1
        else
            isfile_cnt[st.desc] = 1
        end
        filemode(st) & 0xf000 == 0x8000
    end
end

empty!(Base.isfile_cnt)

using Pkg
Pkg.precompile()

@show sort(collect(Base.isfile_cnt); by=x->x[2], rev=true)

gives for a big environment (e.g. DifferentialEquations.jl):

"~/.julia/compiled/v1.10/Preferences/pWSk8_J52EP.ji"         => 152
"~/.julia/compiled/v1.10/Preferences/pWSk8_bmGsQ.ji"         => 152
"~/julia/compiled/v1.10/SuiteSparse_jll/ME9At_BncKj.ji"      => 124
"~/julia/compiled/v1.10/SuiteSparse_jll/ME9At_rJPx9.ji"      => 124
"~/julia/compiled/v1.10/SuiteSparse_jll/ME9At_9T2BZ.ji"      => 124
"~/.julia/compiled/v1.10/PrecompileTools/AQ9Mk_bmGsQ.ji"     => 123
"~/.julia/compiled/v1.10/PrecompileTools/AQ9Mk_J52EP.ji"     => 123
"~/julia/compiled/v1.10/SparseArrays/P9ieR_eNkqo.ji"         => 122
"~/julia/compiled/v1.10/SparseArrays/P9ieR_BncKj.ji"         => 122
"~/julia/compiled/v1.10/SparseArrays/P9ieR_rJPx9.ji"         => 122
"~/.julia/compiled/v1.10/ArrayInterface/7bROb_EHPmX.ji"      => 112
"~/.julia/compiled/v1.10/DocStringExtensions/KRdZs_bmGsQ.ji" => 111

where we are checking the same file over and over.

This seems to come from

julia/base/loading.jl

Line 1834 in 2cdfe06

modpaths = find_all_in_cache_path(modkey)

Noticed by @topolarity when a no-op instantiate was slow on Windows