Mmap fix on system with 64k pagesize. (#59695)

Not sure if this is the best approach but seemed to allow Mmap test to
pass. Seems the pagesize was being set to value at build-time rather
than being re-evaluated at runtime. Running Mmap tests on system with
64k pagesize, Mmap would still think its on a system with 4k pagesize
and therefore fail.

---------

Co-authored-by: Jameson Nash <[email protected]>

Author: green-br

base/sysinfo.jl

@@ -14,6 +14,7 @@ export BINDIR,
        MACHINE,
        KERNEL,
        JIT,
+       PAGESIZE,
        cpu_info,
        cpu_summary,
        sysimage_target,
@@ -144,6 +145,13 @@ Note: Included in the detailed system information via `versioninfo(verbose=true)
 """
 global JIT::String
 
+"""
+    Sys.PAGESIZE::Clong
+
+A number providing the pagesize of the given OS.  Common values being 4kb or 64kb on Linux.
+"""
+global PAGESIZE::Clong
+
 function __init__()
     env_threads = nothing
     if haskey(ENV, "JULIA_CPU_THREADS")
@@ -162,6 +170,7 @@ function __init__()
     global SC_CLK_TCK = ccall(:jl_SC_CLK_TCK, Clong, ())
     global CPU_NAME = ccall(:jl_get_cpu_name, Ref{String}, ())
     global JIT = ccall(:jl_get_JIT, Ref{String}, ())
+    global PAGESIZE = Int(Sys.isunix() ? ccall(:jl_getpagesize, Clong, ()) : ccall(:jl_getallocationgranularity, Clong, ()))
     __init_build()
     nothing
 end

stdlib/Mmap/src/Mmap.jl

@@ -6,11 +6,10 @@ Low level module for mmap (memory mapping of files).
 module Mmap
 
 import Base: OS_HANDLE, INVALID_OS_HANDLE
+using Base.Sys: PAGESIZE
 
 export mmap
 
-const PAGESIZE = Int(Sys.isunix() ? ccall(:jl_getpagesize, Clong, ()) : ccall(:jl_getallocationgranularity, Clong, ()))
-
 # for mmaps not backed by files
 mutable struct Anonymous <: IO
     name::String

stdlib/Mmap/test/runtests.jl

@@ -269,6 +269,7 @@ A2 = mmap(s, Matrix{Int}, (m,n))
 seek(s, 0)
 A3 = mmap(s, Matrix{Int}, (m,n), convert(Int64, 2*sizeof(Int)))
 @test A == A3
+seek(s, 0)
 A4 = mmap(s, Matrix{Int}, (m,150), convert(Int64, (2+150*m)*sizeof(Int)))
 @test A[:, 151:end] == A4
 close(s)