From: Robert Haas <rhaas@postgresql.org>
Date: Thu, 10 Apr 2014 20:01:52 +0000 (+0000)
Subject: Push obsize/nmax computation down.
X-Git-Url: http://git.postgresql.org/gitweb/static/close/reject?a=commitdiff_plain;h=4504aff4f4b69cd254cbdceed7d09bcd71bc9daa;p=users%2Frhaas%2Fpostgres.git

Push obsize/nmax computation down.

Testing shows this is faster (5.4s vs 5.7s for 100m 8-byte allocations).
---

diff --git a/src/backend/utils/mmgr/sb_alloc.c b/src/backend/utils/mmgr/sb_alloc.c
index 31d4eee7c9..bf4b0586c5 100644
--- a/src/backend/utils/mmgr/sb_alloc.c
+++ b/src/backend/utils/mmgr/sb_alloc.c
@@ -110,8 +110,7 @@ static char sb_size_class_map[] = {
 #define SB_NUM_SIZE_CLASSES				lengthof(sb_size_classes)
 
 /* Helper functions. */
-static char *sb_alloc_from_heap(char *base, sb_heap *heap,
-				   Size obsize, Size nmax);
+static char *sb_alloc_from_heap(char *base, sb_heap *heap, int size_class);
 static char *sb_alloc_guts(char *base, sb_region *region,
 			  sb_allocator *a, int size_class);
 static void sb_init_span(char *base, sb_span *span, sb_heap *heap,
@@ -345,12 +344,22 @@ sb_reset_allocator(sb_allocator *a)
  * superblock that would otherwise become empty soon.
  */
 static char *
-sb_alloc_from_heap(char *base, sb_heap *heap, Size obsize, Size nmax)
+sb_alloc_from_heap(char *base, sb_heap *heap, int size_class)
 {
 	sb_span *active_sb;
 	Size	fclass;
 	char   *superblock;
 	char   *result;
+	Size	obsize;
+	Size	nmax;
+
+	/* Work out object size. */
+	Assert(size_class < SB_NUM_SIZE_CLASSES);
+	obsize = sb_size_classes[size_class];
+	if (size_class == 0)
+ 		nmax = FPM_PAGE_SIZE / obsize;
+	else
+ 		nmax = (FPM_PAGE_SIZE * SB_PAGES_PER_SUPERBLOCK) / obsize;
 
 	/*
 	 * If fullness class 1 is empty, try to find something to put in it by
@@ -461,23 +470,13 @@ sb_alloc_guts(char *base, sb_region *region, sb_allocator *a, int size_class)
 	sb_heap *heap = &a->heaps[size_class];
 	LWLock *lock = relptr_access(base, heap->lock);
 	char *result = NULL;
-	Size	obsize;
-	Size	nmax;
-
-	/* Work out object size. */
-	Assert(size_class < SB_NUM_SIZE_CLASSES);
-	obsize = sb_size_classes[size_class];
-	if (size_class == 0)
- 		nmax = FPM_PAGE_SIZE / obsize;
-	else
- 		nmax = (FPM_PAGE_SIZE * SB_PAGES_PER_SUPERBLOCK) / obsize;
 
 	/* If locking is in use, acquire the lock. */
 	if (lock != NULL)
 		LWLockAcquire(lock, LW_EXCLUSIVE);
 
 	/* Attempt to allocate from the heap. */
-	result = sb_alloc_from_heap(base, heap, obsize, nmax);
+	result = sb_alloc_from_heap(base, heap, size_class);
 
 	/*
 	 * If there's no space in the current heap, but there are multiple heaps
@@ -489,7 +488,7 @@ sb_alloc_guts(char *base, sb_region *region, sb_allocator *a, int size_class)
 		if (sb_try_to_steal_superblock(base, a, size_class))
 		{
 			/* The superblock we stole shouldn't full, so this should work. */
-			result = sb_alloc_from_heap(base, heap, obsize, nmax);
+			result = sb_alloc_from_heap(base, heap, size_class);
 			Assert(result != NULL);
 		}
 		else
@@ -548,7 +547,7 @@ sb_alloc_guts(char *base, sb_region *region, sb_allocator *a, int size_class)
 				span->ninitialized = span->nused = 1;
 
 			/* This should work now. */
-			result = sb_alloc_from_heap(base, heap, obsize, nmax);
+			result = sb_alloc_from_heap(base, heap, size_class);
 			Assert(result != NULL);
 		}
 	}