From: Robert Haas <rhaas@postgresql.org>
Date: Tue, 29 Apr 2014 17:17:41 +0000 (-0400)
Subject: Finish up sb_free.
X-Git-Url: http://git.postgresql.org/gitweb/static/gitweb.js?a=commitdiff_plain;h=5f2d36c19c4c99d81987f607cc9db9df23c49d7f;p=users%2Frhaas%2Fpostgres.git

Finish up sb_free.
---

diff --git a/src/backend/utils/mmgr/sb_alloc.c b/src/backend/utils/mmgr/sb_alloc.c
index 70eb9c75a0..7082047d20 100644
--- a/src/backend/utils/mmgr/sb_alloc.c
+++ b/src/backend/utils/mmgr/sb_alloc.c
@@ -347,9 +347,13 @@ sb_free(void *ptr)
 		FreePageManagerPut(region->fpm, first_page, span->npages);
 
 		/*
-		 * XXX. Free the span, and possibly the span-of-spans which contains
-		 * it.
+		 * Span-of-spans superblocks store the span which describes them
+		 * within the superblock itself, so freeing the storage implicitly
+		 * frees the descriptor also.  If this is a superblock of any other
+		 * type, we need to separately free the span object also.
 		 */
+		if (span->size_class != SB_SCLASS_SPAN_OF_SPANS)
+			sb_free(span);
 	}
 
 	/* If we locked the heap, release the lock. */
@@ -516,10 +520,12 @@ sb_ensure_active_superblock(char *base, sb_region *region, sb_allocator *a,
 
 	/*
 	 * Compute the number of objects that will fit in a superblock of this
-	 * size class.
+	 * size class.  Span-of-spans superblocks are just a single page, and the
+	 * first object isn't available for use because it describes the
+	 * span-of-spans itself.
 	 */
 	if (size_class == SB_SCLASS_SPAN_OF_SPANS)
-		nmax = FPM_PAGE_SIZE / obsize;
+		nmax = FPM_PAGE_SIZE / obsize - 1;
 	else
  		nmax = SB_SUPERBLOCK_SIZE / obsize;
 
@@ -635,12 +641,6 @@ sb_ensure_active_superblock(char *base, sb_region *region, sb_allocator *a,
 	for (i = 0; i < npages; ++i)
 		sb_map_set(region->pagemap, first_page + i, span);
 
-	/* For a span-of-spans, record that we allocated ourselves. */
-	if (size_class == SB_SCLASS_SPAN_OF_SPANS)
-	{
-		span->ninitialized = 1;
-		span->nallocatable--;
-	}
 	return true;
 }
 
@@ -665,7 +665,17 @@ sb_init_span(char *base, sb_span *span, sb_heap *heap, char *ptr,
 	span->size_class = size_class;
 	span->ninitialized = 0;
 	if (size_class == SB_SCLASS_SPAN_OF_SPANS)
- 		span->nallocatable = FPM_PAGE_SIZE / obsize;
+	{
+		/*
+		 * A span-of-spans contains its own descriptor, so mark one object
+		 * as initialized and reduce the count of allocatable objects by one.
+		 * Doing this here has the side effect of also reducing nmax by one,
+		 * which is important to make sure we free this object at the correct
+		 * time.
+		 */
+		span->ninitialized = 1;
+ 		span->nallocatable = FPM_PAGE_SIZE / obsize - 1;
+	}
 	else if (size_class != SB_SCLASS_SPAN_LARGE)
  		span->nallocatable = SB_SUPERBLOCK_SIZE / obsize;
 	span->firstfree = SB_SPAN_NOTHING_FREE;