From: Eric Wong <normalperson@...>
Date: 2018-06-21T23:06:48+00:00
Subject: [ruby-core:87584] Re: [Ruby trunk Bug#14858] Introduce 2nd GC heap named Transient heap

ko1@atdot.net wrote:
> https://bugs.ruby-lang.org/issues/14858

Thanks, I can confirm a good result with this.  However, 32k
is too small to be worth using mmap on.
And maybe mmap is unnecessary (and bad for portability).

Using malloc, I seem to get a tiny improvement in space and time:

```
--- a/transient_heap.c
+++ b/transient_heap.c
@@ -237,10 +237,8 @@ static struct transient_heap_block *
 transient_heap_block_alloc(struct transient_heap* theap)
 {
     struct transient_heap_block *block;
-    block = mmap(NULL, TRANSIENT_HEAP_BLOCK_SIZE, PROT_READ | PROT_WRITE,
-                 MAP_PRIVATE | MAP_ANONYMOUS,
-                 -1, 0);
-    if (block == MAP_FAILED) rb_bug("transient_heap_block_alloc: err:%d\n", errno);
+    block = malloc(TRANSIENT_HEAP_BLOCK_SIZE);
+    if (!block) rb_bug("transient_heap_block_alloc: err:%d\n", errno);
 
     reset_block(block);
 
@@ -501,12 +499,7 @@ transient_heap_reset(void)
         theap->total_objects -= block->info.objects;
 #if TRANSIENT_HEAP_INFINITE_BLOCK_MODE
         // debug mode
-        if (madvise(block, TRANSIENT_HEAP_BLOCK_SIZE, MADV_DONTNEED) != 0) {
-            rb_bug("madvise err:%d", errno);
-        }
-        if (mprotect(block, TRANSIENT_HEAP_BLOCK_SIZE, PROT_NONE) != 0) {
-            rb_bug("mprotect err:%d", errno);
-        }
+        free(block);
         theap->total_blocks--;
 #else
         reset_block(block);
```

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