Hi all Attached is a patch to libgc that will allow it to actually unmap memory when USE_MUNMAP is defined. Currently, the unmap code just sets the mmap flags on a region to 'no access'. The patch unlinks blocks from the gc free list larger than a defined min size (currently 4k bytes), that haven't been used for several collections, and unmaps the memory.
It may or may not fix https://bugzilla.novell.com/show_bug.cgi?id=495486 - the reporter forgot to attach his test case. Comments? - Dick
Index: include/private/gc_priv.h
===================================================================
--- include/private/gc_priv.h (revision 137556)
+++ include/private/gc_priv.h (working copy)
@@ -253,6 +253,8 @@
/* the block risks unreasonable immediate */
/* heap growth. */
+# define REALLY_FREE_MIN 4096
+
/*********************************/
/* */
/* Stack saving for debugging */
@@ -908,6 +910,7 @@
# endif
# ifdef USE_MUNMAP
word _unmapped_bytes;
+ word _really_unmapped_bytes;
# endif
# ifdef MERGE_SIZES
unsigned _size_map[WORDS_TO_BYTES(MAXOBJSZ+1)];
@@ -1054,6 +1057,7 @@
# define GC_last_stack GC_arrays._last_stack
# ifdef USE_MUNMAP
# define GC_unmapped_bytes GC_arrays._unmapped_bytes
+# define GC_really_unmapped_bytes GC_arrays._really_unmapped_bytes
# endif
# if defined(MSWIN32) || defined(MSWINCE)
# define GC_heap_bases GC_arrays._heap_bases
@@ -1780,6 +1784,7 @@
void GC_unmap(ptr_t start, word bytes);
void GC_remap(ptr_t start, word bytes);
void GC_unmap_gap(ptr_t start1, word bytes1, ptr_t start2, word bytes2);
+ void GC_really_unmap(ptr_t start, word bytes);
#endif
/* Virtual dirty bit implementation: */
Index: ChangeLog
===================================================================
--- ChangeLog (revision 137556)
+++ ChangeLog (working copy)
@@ -1,3 +1,8 @@
+2009-08-13 Dick Porter <dpor...@codicesoftware.com>
+
+ * include/private/gc_priv.h, allchblk.c, os_dep.c: Cause libgc to
+ return unused memory to the system in some cases.
+
2009-04-28 Zoltan Varga <var...@gmail.com>
* misc.c (GC_init): Avoid casting an lvalue. Fixes part of #498692.
Index: allchblk.c
===================================================================
--- allchblk.c (revision 137556)
+++ allchblk.c (working copy)
@@ -364,7 +364,7 @@
/* way blocks are ever unmapped. */
void GC_unmap_old(void)
{
- struct hblk * h;
+ struct hblk * h, * next;
hdr * hhdr;
word sz;
unsigned short last_rec, threshold;
@@ -372,8 +372,9 @@
# define UNMAP_THRESHOLD 6
for (i = 0; i <= N_HBLK_FLS; ++i) {
- for (h = GC_hblkfreelist[i]; 0 != h; h = hhdr -> hb_next) {
+ for (h = GC_hblkfreelist[i]; 0 != h; h = next) {
hhdr = HDR(h);
+ next = hhdr -> hb_next;
if (!IS_MAPPED(hhdr)) continue;
threshold = (unsigned short)(GC_gc_no - UNMAP_THRESHOLD);
last_rec = hhdr -> hb_last_reclaimed;
@@ -382,6 +383,16 @@
sz = hhdr -> hb_sz;
GC_unmap((ptr_t)h, sz);
hhdr -> hb_flags |= WAS_UNMAPPED;
+
+#if !defined(MSWIN32) && !defined(MSWINCE)
+ if (sz > REALLY_FREE_MIN) {
+ GC_remove_from_fl(hhdr, i);
+ GC_remove_header(h);
+
+ /* Now really unmap the block */
+ GC_really_unmap ((ptr_t)h, sz);
+ }
+#endif
}
}
}
@@ -412,6 +423,7 @@
/* make both consistent, so that we can merge */
if (size > nextsize) {
GC_remap((ptr_t)next, nextsize);
+ nexthdr -> hb_flags &= ~WAS_UNMAPPED;
} else {
GC_unmap((ptr_t)h, size);
hhdr -> hb_flags |= WAS_UNMAPPED;
Index: os_dep.c
===================================================================
--- os_dep.c (revision 137556)
+++ os_dep.c (working copy)
@@ -1966,6 +1966,23 @@
# endif
}
+void GC_really_unmap(ptr_t start, word bytes)
+{
+ ptr_t start_addr = GC_unmap_start(start, bytes);
+ ptr_t end_addr = GC_unmap_end(start, bytes);
+ word len = end_addr - start_addr;
+ if (0 == start_addr) return;
+# if defined(MSWIN32) || defined(MSWINCE)
+ /* No idea what to do here */
+# else
+ {
+ int result;
+ result = munmap(start_addr, len);
+ if (result != 0) ABORT("munmap() failed");
+ }
+ GC_really_unmapped_bytes += len;
+# endif
+}
#endif /* USE_MUNMAP */
/* Routine for pushing any additional roots. In THREADS */
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