X Split PAGE_LOADED -> PAGE_LOADED, PAGE_LOADED_FOR_WRITE

The latter state is the only valid state in wcfs mode when pagefault
handler sees already loaded page in fileh->pagemap.

bigfile/tests/test_virtmem.c

@@ -1282,7 +1282,7 @@ int main()
 {
     tap_fail_callback = abort;  // XXX to catch failure immediately
 
-  if (0) {
+  if (1) {
     test_vmamap();
     test_file_access_synthetic();
     test_file_access_pagefault();

bigfile/virtmem.c

@@ -479,6 +479,7 @@ void fileh_invalidate_page(BigFileH *fileh, pgoff_t pgoffset)
     BUG_ON(fileh->writeout_inprogress);
     // XXX wcfs: invalidate_page must not be called (wcfs handles invalidations itself)
     // XXX       or allow invalidate anyway (e.g. DIRTY -> base) ?
+    // XXX yes -> allow invalidate for wcfs too - means forget in-ram page and mmap to base memory
 
     page = pagemap_get(&fileh->pagemap, pgoffset);
     if (page) {
@@ -630,12 +631,17 @@ VMFaultResult vma_on_pagefault(VMA *vma, uintptr_t addr, int write)
     /* (3) fileh, pagen -> page  (via pagemap) */
     page = pagemap_get(&fileh->pagemap, pagen);
 
-    /* wcfs: all dirty pages are mmapped when vma is created */
-    // FIXME no: it could be in PAGE_LOADING state
-    // XXX and after VM_RETRY it could be in PAGE_LOADED state
-    // XXX ----//----                        even for write
-    if (vma->mmap_overlay)
-        BUG_ON(page);
+    /* wcfs: all dirty pages are mmapped when vma is created.
+     *       thus here, if page is present in pagemap, it can be only either
+     *       - a page we just loaded for dirtying, or
+     *       - a page that is in progress of being loaded.
+     *
+     * ( PAGE_LOADED_FOR_WRITE is used only to verify that in wcfs mode we
+     *   always keep all dirty pages mmapped on fileh_open and so pagefault
+     *   handler must not see a PAGE_LOADED page. )
+     */
+    if (vma->mmap_overlay && page)
+        ASSERT(page->state == PAGE_LOADED_FOR_WRITE || page->state == PAGE_LOADING);
 
     /* (4) no page found - allocate new from ram */
     while (!page) {
@@ -705,9 +711,6 @@ VMFaultResult vma_on_pagefault(VMA *vma, uintptr_t addr, int write)
         pageram = page_mmap(page, NULL, PROT_READ | PROT_WRITE);
         TODO(!pageram); // XXX err
 
-        // XXX overlay: copy data from base image, page.state=DIRTY
-        // XXX overlay: goto inject_page
-
         /* load block -> pageram memory */
         blk = page->f_pgoffset;     // NOTE because blksize = pagesize
 
@@ -755,7 +758,7 @@ VMFaultResult vma_on_pagefault(VMA *vma, uintptr_t addr, int write)
 
         /* else just mark the page as loaded ok */
         else
-            page->state = PAGE_LOADED;
+            page->state = (write ? PAGE_LOADED_FOR_WRITE : PAGE_LOADED);
 
         /* we have to retry the whole fault, because the vma could have been
          * changed while we were loading page with virtmem lock released */
@@ -785,7 +788,6 @@ VMFaultResult vma_on_pagefault(VMA *vma, uintptr_t addr, int write)
         return VM_RETRY;
     }
 
-//inject_page:
     /* (6) page data ready. Mmap it atomically into vma address space, or mprotect
      * appropriately if it was already mmaped. */
     int prot = PROT_READ;
@@ -853,7 +855,7 @@ static int __ram_reclaim(RAM *ram)
 
         /* can release ram only from loaded non-dirty pages
          * NOTE PAGE_LOADING pages are not dropped - they just continue to load */
-        if (page->state == PAGE_LOADED) {
+        if (page->state == PAGE_LOADED || page->state == PAGE_LOADED_FOR_WRITE) {
             page_drop_memory(page);
             batch--;
         }

include/wendelin/bigfile/virtmem.h

@@ -84,7 +84,9 @@ enum PageState {
                     = 2, /* file content              loading was in progress
                             while request to invalidate the page came in */
     PAGE_LOADED     = 3, /* file content has     been loaded and was not modified */
-    PAGE_DIRTY      = 4, /* file content has     been loaded and was     modified */
+    PAGE_LOADED_FOR_WRITE
+                    = 4, /* file content has     been loaded and is going to be modified */
+    PAGE_DIRTY      = 5, /* file content has     been loaded and was     modified */
 };
 typedef enum PageState PageState;