slru-truncate-modulo-v1.patch

diff --git a/src/backend/access/transam/slru.c b/src/backend/access/transam/slru.c
index 3623352..843486a 100644
--- a/src/backend/access/transam/slru.c
+++ b/src/backend/access/transam/slru.c
@@ -1171,11 +1171,6 @@ SimpleLruTruncate(SlruCtl ctl, int cutoffPage)
 	int			slotno;
 
 	/*
-	 * The cutoff point is the start of the segment containing cutoffPage.
-	 */
-	cutoffPage -= cutoffPage % SLRU_PAGES_PER_SEGMENT;
-
-	/*
 	 * Scan shared memory and remove any pages preceding the cutoff page, to
 	 * ensure we won't rewrite them later.  (Since this is normally called in
 	 * or just after a checkpoint, any dirty pages should have been flushed
@@ -1320,11 +1315,10 @@ restart:
 bool
 SlruScanDirCbReportPresence(SlruCtl ctl, char *filename, int segpage, void *data)
 {
+	int			seg_last_page = segpage + SLRU_PAGES_PER_SEGMENT - 1;
 	int			cutoffPage = *(int *) data;
 
-	cutoffPage -= cutoffPage % SLRU_PAGES_PER_SEGMENT;
-
-	if (ctl->PagePrecedes(segpage, cutoffPage))
+	if (ctl->PagePrecedes(seg_last_page, cutoffPage))
 		return true;			/* found one; don't iterate any more */
 
 	return false;				/* keep going */
@@ -1337,9 +1331,10 @@ SlruScanDirCbReportPresence(SlruCtl ctl, char *filename, int segpage, void *data
 static bool
 SlruScanDirCbDeleteCutoff(SlruCtl ctl, char *filename, int segpage, void *data)
 {
+	int			seg_last_page = segpage + SLRU_PAGES_PER_SEGMENT - 1;
 	int			cutoffPage = *(int *) data;
 
-	if (ctl->PagePrecedes(segpage, cutoffPage))
+	if (ctl->PagePrecedes(seg_last_page, cutoffPage))
 		SlruInternalDeleteSegment(ctl, filename);
 
 	return false;				/* keep going */