Re: impressions on gc

[Chris K. Jester-Young]

On Fri, Dec 02, 2011 at 12:09:12AM +0100, Andy Wingo wrote:
> One change was to make GC run more often when a process is growing, in
> terms of resident memory size.  This seems to be a good idea in general.
> 
> The other was to add a function that users can call to note
> non-gc-managed allocations -- allocations that may be freed when GC is
> run, but which the GC doesn't know about.  That is
> scm_gc_register_allocation.  This routine runs GC after allocated bytes
> exceed some limit, currently the GC-managed heap size, reset after every
> GC.  This is to catch steady-state mallocation.

I looked at the change for it, fd51e66190bde8cef74fec9725de4da3471901c4.
It looks cool. :-)

Alas, part of that diff also breaks libgc 7.1 (which is the version that
Debian currently has packaged), which lack the unmapping functions.
Here's my diff to make it work again.

Many thanks,
Chris.

                        *       *       *

diff --git a/configure.ac b/configure.ac
index d63dd63..0cfe961 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1259,7 +1259,7 @@ save_LIBS="$LIBS"
 LIBS="$BDW_GC_LIBS $LIBS"
 CFLAGS="$BDW_GC_CFLAGS $CFLAGS"
 
-AC_CHECK_FUNCS([GC_do_blocking GC_call_with_gc_active GC_pthread_exit 
GC_pthread_cancel GC_allow_register_threads GC_pthread_sigmask 
GC_set_start_callback GC_get_heap_usage_safe GC_get_free_space_divisor])
+AC_CHECK_FUNCS([GC_do_blocking GC_call_with_gc_active GC_pthread_exit 
GC_pthread_cancel GC_allow_register_threads GC_pthread_sigmask 
GC_set_start_callback GC_get_heap_usage_safe GC_get_free_space_divisor 
GC_gcollect_and_unmap GC_get_unmapped_bytes])
 
 # Though the `GC_do_blocking ()' symbol is present in GC 7.1, it is not
 # declared, and has a different type (returning void instead of
diff --git a/libguile/gc-malloc.c b/libguile/gc-malloc.c
index 72142ca..b7781f3 100644
--- a/libguile/gc-malloc.c
+++ b/libguile/gc-malloc.c
@@ -96,7 +96,11 @@ scm_realloc (void *mem, size_t size)
     return ptr;
 
   /* Time is hard: trigger a full, ``stop-the-world'' GC, and try again.  */
+#ifdef HAVE_GC_GCOLLECT_AND_UNMAP
   GC_gcollect_and_unmap ();
+#else
+  GC_gcollect ();
+#endif
 
   SCM_SYSCALL (ptr = realloc (mem, size));
   if (ptr)
diff --git a/libguile/gc.c b/libguile/gc.c
index ff1ebe6..0ab27a5 100644
--- a/libguile/gc.c
+++ b/libguile/gc.c
@@ -205,7 +205,11 @@ GC_get_heap_usage_safe (GC_word *pheap_size, GC_word 
*pfree_bytes,
 {
   *pheap_size = GC_get_heap_size ();
   *pfree_bytes = GC_get_free_bytes ();
+#ifdef HAVE_GC_GET_UNMAPPED_BYTES
   *punmapped_bytes = GC_get_unmapped_bytes ();
+#else
+  *punmapped_bytes = 0;
+#endif
   *pbytes_since_gc = GC_get_bytes_since_gc ();
   *ptotal_bytes = GC_get_total_bytes ();
 }