2 files changed, 18 insertions, 6 deletions
diff --git a/vendor/modernc.org/memory/memory.go b/vendor/modernc.org/memory/memory.go
index e25acda9b..6593c4234 100644
--- a/vendor/modernc.org/memory/memory.go
+++ b/vendor/modernc.org/memory/memory.go
@@ -109,6 +109,12 @@ func (a *Allocator) mmap(size int) (uintptr /* *page */, error) {
 		return 0, err
 	}
 
+	//TODO(jnml) The returned size may now be nearly as twice as large as we asked
+	//for. Use that extra capacity. For that we need to move the respective
+	//Allocator.cap item into the page struct so the page cap becomes dynamic.
+	//
+	// Related: This is a consequence of fixing the bigsort.test failures on
+	// linux/s390x, see: https://gitlab.com/cznic/sqlite/-/issues/207
 	if counters {
 		a.Mmaps++
 		a.Bytes += size
diff --git a/vendor/modernc.org/memory/mmap_unix.go b/vendor/modernc.org/memory/mmap_unix.go
index ef6c9a539..8ee991538 100644
--- a/vendor/modernc.org/memory/mmap_unix.go
+++ b/vendor/modernc.org/memory/mmap_unix.go
@@ -14,7 +14,7 @@ import (
 	"unsafe"
 )
 
-const pageSizeLog = 20
+const pageSizeLog = 16
 
 var (
 	osPageMask = osPageSize - 1
@@ -28,21 +28,23 @@ func unmap(addr uintptr, size int) error {
 // pageSize aligned.
 func mmap(size int) (uintptr, int, error) {
 	size = roundup(size, osPageSize)
-	up, err := unix.MmapPtr(-1, 0, nil, uintptr(size+pageSize), unix.PROT_READ|unix.PROT_WRITE, unix.MAP_PRIVATE|unix.MAP_ANON)
+	// Ask for more so we can align the result at a pageSize boundary
+	n := size + pageSize
+	up, err := unix.MmapPtr(-1, 0, nil, uintptr(n), unix.PROT_READ|unix.PROT_WRITE, unix.MAP_PRIVATE|unix.MAP_ANON)
 	if err != nil {
 		return 0, 0, err
 	}
 
 	p := uintptr(up)
-	n := size + pageSize
 	if p&uintptr(osPageMask) != 0 {
 		panic("internal error")
 	}
 
 	mod := int(p) & pageMask
-	if mod != 0 {
+	if mod != 0 { // Return the extra part before pageSize aligned block
 		m := pageSize - mod
 		if err := unmap(p, m); err != nil {
+			unmap(p, n) // Do not leak the first mmap
 			return 0, 0, err
 		}
 
@@ -54,9 +56,13 @@ func mmap(size int) (uintptr, int, error) {
 		panic("internal error")
 	}
 
-	if n-size != 0 {
+	if n > size { // Return the extra part after pageSize aligned block
 		if err := unmap(p+uintptr(size), n-size); err != nil {
-			return 0, 0, err
+			// Do not error when the kernel rejects the extra part after, just return the
+			// unexpectedly enlarged size.
+			//
+			// Fixes the bigsort.test failures on linux/s390x, see: https://gitlab.com/cznic/sqlite/-/issues/207
+			size = n
 		}
 	}