Limit number of unmapped regions (Linux)

Issue #324 (bdwgc).

When the number of areas exceeds vm.max_map_count on Linux (~65530 by
default) then the mmap call in GC_unmap fails with ENOMEM.
This commit fixes the issue by establishing a soft limit on the
number of unmapped regions.

* allchblk.c (get_block_ending_at): New static function.
* allchblk.c [USE_MUNMAP && COUNT_UNMAPPED_REGIONS]
(calc_num_unmapped_regions_delta): Likewise.
* allchblk.c (GC_free_block_ending_at): Use get_block_ending_at().
* allchblk.c [GC_adjust_num_unmapped] (GC_adjust_num_unmapped): New
inline function.
* allchblk.c [USE_MUNMAP && COUNT_UNMAPPED_REGIONS] (GC_unmap_old):
Skip unmapping if GC_num_unmapped_regions exceeds
GC_UNMAPPED_REGIONS_SOFT_LIMIT, update GC_num_unmapped_regions value
otherwise (before GC_unmap).
* allchblk.c [USE_MUNMAP] (GC_merge_unmapped, GC_allochblk_nth): Call
GC_adjust_num_unmapped() before GC_remap() and GC_unmap().
* headers.c (GC_next_used_block, GC_prev_block): Move/refine comment
to gc_priv.h.
* headers.c (GC_next_used_block): Rename to GC_next_block and add
allow_free parameter.
* include/private/gc_priv.h (GC_next_used_block): Likewise.
* include/private/gc_priv.h [USE_MUNMAP && COUNT_UNMAPPED_REGIONS]
(_GC_arrays): Add _num_unmapped_regions field.
* include/private/gcconfig.h [(M68K || POWERPC || SPARC || I386
|| MIPS || OR1K || ALPHA || IA64 || S390 || AARCH64 || ARM32 || CRIS
|| SH && !SH4 || AVR32 || M32R || X86_64 || HEXAGON || TILEPRO
|| TILEGX || RISCV) && LINUX] (COUNT_UNMAPPED_REGIONS): Define macro.
* include/private/gcconfig.h [USE_MUNMAP && COUNT_UNMAPPED_REGIONS
&& !GC_UNMAPPED_REGIONS_SOFT_LIMIT] (GC_UNMAPPED_REGIONS_SOFT_LIMIT):
Likewise.
* os_dep.c [USE_MUNMAP] (GC_unmap_end): Move to gc_priv.h and make it
inline.
* mark.c (GC_push_next_marked, GC_push_next_marked_dirty,
GC_push_next_marked_uncollectable): Use GC_next_block(h, FALSE)
instead of GC_next_used_block(h).

1 files changed, 5 insertions, 9 deletions

diff --git a/headers.c b/headers.c
index a1ab35a3..c71449f1 100644
--- a/headers.c
+++ b/headers.c
@@ -333,9 +333,7 @@ void GC_apply_to_all_blocks(void (*fn)(struct hblk *h, word client_data),
      }
 }
 
-/* Get the next valid block whose address is at least h */
-/* Return 0 if there is none.                           */
-GC_INNER struct hblk * GC_next_used_block(struct hblk *h)
+GC_INNER struct hblk * GC_next_block(struct hblk *h, GC_bool allow_free)
 {
     REGISTER bottom_index * bi;
     REGISTER word j = ((word)h >> LOG_HBLKSIZE) & (BOTTOM_SZ-1);
@@ -349,14 +347,15 @@ GC_INNER struct hblk * GC_next_used_block(struct hblk *h)
         while (bi != 0 && bi -> key < hi) bi = bi -> asc_link;
         j = 0;
     }
-    while(bi != 0) {
+
+    while (bi != 0) {
         while (j < BOTTOM_SZ) {
             hdr * hhdr = bi -> index[j];
             if (IS_FORWARDING_ADDR_OR_NIL(hhdr)) {
                 j++;
             } else {
-                if (!HBLK_IS_FREE(hhdr)) {
-                    return((struct hblk *)
+                if (allow_free || !HBLK_IS_FREE(hhdr)) {
+                    return ((struct hblk *)
                               (((bi -> key << LOG_BOTTOM_SZ) + j)
                                << LOG_HBLKSIZE));
                 } else {
@@ -370,9 +369,6 @@ GC_INNER struct hblk * GC_next_used_block(struct hblk *h)
     return(0);
 }
 
-/* Get the last (highest address) block whose address is        */
-/* at most h.  Return 0 if there is none.                       */
-/* Unlike the above, this may return a free block.              */
 GC_INNER struct hblk * GC_prev_block(struct hblk *h)
 {
     bottom_index * bi;