fix: gc policy for windows to use 10% of disk space

Initially we had the GC Policy for Windows use only
2 GB (2e9 bytes) of disk space and this was limiting
for some build scenarios that need more than that,
especially ServerCore images.

This commit makes the policy to use percentages
as it is on Linux. Also going for 10% as it is
on Linux. For instance, after the change, on a
dev machine, the configured space was
74694367232 / (1 << 30) = 69.5 GiB.

fixes #4858 docker/buildx#2411

Signed-off-by: Anthony Nandaa <[email protected]>

cmd/buildkitd/config/gcpolicy_windows.go

@@ -3,10 +3,36 @@
 
 package config
 
+import "golang.org/x/sys/windows"
+
 func DetectDefaultGCCap() DiskSpace {
-	return DiskSpace{Bytes: defaultCap}
+	return DiskSpace{Percentage: 10}
 }
 
 func (d DiskSpace) AsBytes(root string) int64 {
-	return d.Bytes
+	if d.Bytes != 0 {
+		return d.Bytes
+	}
+	if d.Percentage == 0 {
+		return 0
+	}
+
+	rootUTF16, err := windows.UTF16FromString(root)
+	if err != nil {
+		return defaultCap
+	}
+	var freeAvailableBytes uint64
+	var totalBytes uint64
+	var totalFreeBytes uint64
+
+	if err := windows.GetDiskFreeSpaceEx(
+		&rootUTF16[0],
+		&freeAvailableBytes,
+		&totalBytes,
+		&totalFreeBytes); err != nil {
+		return defaultCap
+	}
+
+	avail := int64(totalBytes) * d.Percentage / 100
+	return avail
 }