add function to query GC page size (#54115)

Author: d-netto

src/gc-pages.c

@@ -9,6 +9,11 @@
 extern "C" {
 #endif
 
+JL_DLLEXPORT uint64_t jl_get_pg_size(void)
+{
+    return GC_PAGE_SZ;
+}
+
 // Try to allocate memory in chunks to permit faster allocation
 // and improve memory locality of the pools
 #ifdef _P64

test/gc.jl

@@ -22,6 +22,12 @@ function run_nonzero_page_utilization_test()
     @test any(page_utilization .> 0)
 end
 
+function run_pg_size_test()
+    page_size = @ccall jl_get_pg_size()::UInt64
+    # supported page sizes: 4KB and 16KB
+    @test page_size == (1 << 12) || page_size == (1 << 14)
+end
+
 # !!! note:
 #     Since we run our tests on 32bit OS as well we confine ourselves
 #     to parameters that allocate about 512MB of objects. Max RSS is lower
@@ -31,7 +37,11 @@ end
     run_gctest("gc/linkedlist.jl")
     run_gctest("gc/objarray.jl")
     run_gctest("gc/chunks.jl")
+end
+
+@testset "GC page metrics" begin
     run_nonzero_page_utilization_test()
+    run_pg_size_test()
 end
 
 @testset "Base.GC docstrings" begin