.

wcfs/client/wcfs.cpp

@@ -71,17 +71,26 @@
 // in FileH._headfsize for use during one transaction.
 //
 //
-//
-//
 // Integration with wendelin.core virtmem layer
 //
-// XXX no need to split mappings on pin
+// Wcfs integrates with virtmem layer to support virtmem to handle dirtying
+// pages of read-only base-layer that wcfs client provides via isolated
+// Mapping. When a page is write-accessed, virtmem mmaps in a page of RAM in
+// place of accessed virtual memory, copies base-layer content into there, and
+// marks that page as read-write accessed.
+//
+// Upon receiving pin message, the pinner consults virtmem, whether
+// corresponding page was already dirtied, and if it was, the pinner does not
+// remmap virtual memory to wcfs/@revX/f and just leaves dirty page in its
+// place, remembering pin information in fileh._pinned.
 //
+// Once dirty pages are no longer needed (either after discard/abort or
+// writeout/commit), virtmem asks wcfs client to remmap corresponding regions
+// of Mapping in its place again.
 //
-// - need to maintain pinner map registry   XXX no need
+// The scheme outlined above avoids splitting Mapping upon dirtying an inner
+// page.
 //
-//      [blk< +len) -> vma      ↓blk
-//      #blk        -> []vma covering it
 //
 // - we can reuse virtmem code:
 //