Keeping un-unmmappable pages until they can be reused

On Linux, munmap() may fail with ENOMEM when virtual memory is too
fragmented. Working this around by just keeping such blocks for future
use.

1 files changed, 17 insertions, 6 deletions

diff --git a/lib/resource.c b/lib/resource.c
index e80b315b..2d041ad5 100644
--- a/lib/resource.c
+++ b/lib/resource.c
@@ -60,7 +60,7 @@ static struct resclass pool_class = {
 pool root_pool;
 
 void *alloc_sys_page(void);
-void free_sys_page(void *);
+int free_sys_page(void *);
 
 static int indent;
 
@@ -98,8 +98,10 @@ pool_free(resource *P)
   if (p->pages)
     {
       ASSERT_DIE(!p->pages->used);
-      for (uint i=0; i<p->pages->free; i++)
+
+      for (uint i = 0; i < p->pages->free; i++)
 	free_sys_page(p->pages->ptr[i]);
+
       free_sys_page(p->pages);
     }
 }
@@ -476,10 +478,19 @@ free_page(pool *p, void *ptr)
   ASSERT_DIE(p->pages);
   p->pages->used--;
 
-  if (p->pages->free >= POOL_PAGES_MAX)
-    return free_sys_page(ptr);
-  else
-    p->pages->ptr[p->pages->free++] = ptr;
+  ASSERT_DIE(p->pages->free <= POOL_PAGES_MAX);
+
+  if (p->pages->free == POOL_PAGES_MAX)
+  {
+    const unsigned long keep = POOL_PAGES_MAX / 4;
+
+    for (uint i = keep; i < p->pages->free; i++)
+      free_sys_page(p->pages->ptr[i]);
+
+    p->pages->free = keep;
+  }
+
+  p->pages->ptr[p->pages->free++] = ptr;
 }