.

wcfs/wcfs_test.py

@@ -270,12 +270,6 @@ class tDB:
         t._wcsync()
         return head
 
-    # _blkaccess marks head/zf[blk] accessed.
-    def _blkaccess(t, zf, blk):
-        # XXX locking
-        zfAccessed = t._accessed.setdefault(zf, {})
-        zfAccessed[blk] = t.head
-
     # _wcsync makes sure wcfs is synchronized to latest committed transaction.
     def _wcsync(t):
         while len(t._wc_zheadv) < len(t.dFtail):
@@ -291,6 +285,13 @@ class tDB:
         # head/at = last txn of whole db
         assert t.read("head/at") == h(t.head)
 
+    # _blkaccess marks head/zf[blk] accessed.
+    # XXX place=?
+    def _blkaccess(t, zf, blk):
+        # XXX locking?
+        zfAccessed = t._accessed.setdefault(zf, {})
+        zfAccessed[blk] = t.head
+
 
     # path returns path for object on wcfs.
     # - str:        wcfs root + obj;
@@ -323,8 +324,7 @@ class tDB:
 
 
     # iter_revv iterates through all possible at_i -> at_j -> at_k ... sequences.
-    # at_i < at_j
-    # NOTE all sequences go till head.
+    # at_i < at_j       NOTE all sequences go till head.
     def iter_revv(t, start=z64, level=0):
         dFtail = [_ for _ in t.dFtail if _.rev > start]
         #print(' '*level, 'iter_revv', t.hat(start), [t.hat(_.rev) for _ in dFtail])
@@ -340,7 +340,7 @@ class tDB:
 
     # _blkData returns expected zf[blk] data and revision as of @at database state.
     #
-    # If the block is hole (b'', at0) is returned.  XXX -> @z64?
+    # If the block is hole - (b'', at0) is returned.  XXX -> @z64?
     # XXX ret for when the file did not existed at all? blk was after file size?
     def _blkData(t, zf, blk, at): # -> (data, rev)
         if at is None:
@@ -412,9 +412,10 @@ class tFile:
         #    stay in pagecache.
         #
         # 2. madvise memory with MADV_SEQUENTIAL and MADV_RANDOM in interleaved
-        #    mode. This adjusts kernel readahead (which triggers for MADV_SEQUENTIAL
-        #    vma) to not go over to next block and thus a read access to one
-        #    block won't trigger implicit read access to its neighbour block.
+        #    mode. This adjusts kernel readahead (which triggers for
+        #    MADV_NORMAL or MADV_SEQUENTIAL vma) to not go over to next block
+        #    and thus a read access to one block won't trigger implicit read
+        #    access to its neighbour block.
         #
         #      https://www.quora.com/What-heuristics-does-the-adaptive-readahead-implementation-in-the-Linux-kernel-use
         #      https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/mm/madvise.c?h=v5.2-rc4#n51
@@ -427,7 +428,7 @@ class tFile:
         #    helps to test how wcfs handles simultaneous read triggered by
         #    async kernel readahead vs wcfs uploading data for the same block
         #    into OS cache. Also, fully enabled readahead is how wcfs is
-        #    actually used.
+        #    actually used in practice.
         assert t.blksize % mm.PAGE_SIZE == 0
         t.fmmap = mm.map_ro(t.f.fileno(), 0, t._max_tracked_pages*t.blksize)
 
@@ -462,6 +463,7 @@ class tFile:
         t.f.close()
 
     # _blk returns memoryview of file[blk].
+    # when/if block memory is accessed, the user has to notify tDB with _blkaccess call.
     def _blk(t, blk):
         assert blk <= t._max_tracked_pages
         return memoryview(t.fmmap[blk*t.blksize:(blk+1)*t.blksize])
@@ -491,7 +493,7 @@ class tFile:
         assert st.st_size // t.blksize <= t._max_tracked_pages
         return st.st_size // t.blksize
 
-    # assertCache asserts state of OS cache for file.
+    # assertCache asserts on state of OS cache for file.
     #
     # incorev is [] of 1/0 representing whether block data is present or not.
     def assertCache(t, incorev):
@@ -537,14 +539,14 @@ class tFile:
         defer(_)
 
         cached = t.cached()[blk]
-        assert cached in (0, 1) # every check access a block in full
+        assert cached in (0, 1) # every check accesses a block in full
         shouldPin = False       # whether at least one wlink should receive a pin
 
         # watches that must be notified if access goes to @head/file
         wpin = {}   # tWatchLink -> pinok
+        if t.at is None: # @head/...
             for wlink in t.tdb._wlinks:
                 pinok = {}
-            if t.at is None: # @head/...
                 w = wlink._watching.get(t.zf)
                 if w is not None and w.at < blkrev:
                     if cached == 1: