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include/wendelin/bigfile/virtmem.h

@@ -75,7 +75,11 @@ struct BigFileH {
     /* whether writeout is currently in progress */
     int writeout_inprogress;
 
-    /* whether base data for all VMAs of this fileh are taken as base-layer mmap XXX */
+    /* whether base data for all VMAs of this fileh are taken as base-layer mmap
+     *
+     * ( we require all VMAs under one fileh to be of the same kind to easily
+     *   make decision whether after writeout to keep a page in RAM or to
+     *   completely drop it not to waste RSS unnecessarily ) */
     // XXX name
     unsigned    mmap_overlay : 1;
 };
@@ -145,9 +149,6 @@ struct VMA {
 
     /* whether corresponding to pgoffset-f_offset page is mapped in this VMA */
     bitmap      *page_ismappedv;    /* len ~ Δaddr / pagesize */
-
-//    // XXX name
-//    unsigned    mmap_overlay : 1;   /* whether base data are taken as file mmap XXX */
 };