Module Name: src
Committed By: manu
Date: Tue Aug 9 06:58:33 UTC 2011
Modified Files:
src/lib/libperfuse: perfuse.c
Log Message:
Remove PUFFS_KFLAG_WTCACHE, which caused data corruption and slowdown
To generate a diff of this commit:
cvs rdiff -u -r1.16 -r1.17 src/lib/libperfuse/perfuse.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/lib/libperfuse/perfuse.c
diff -u src/lib/libperfuse/perfuse.c:1.16 src/lib/libperfuse/perfuse.c:1.17
--- src/lib/libperfuse/perfuse.c:1.16 Tue Jun 28 16:19:16 2011
+++ src/lib/libperfuse/perfuse.c Tue Aug 9 06:58:33 2011
@@ -1,4 +1,4 @@
-/* $NetBSD: perfuse.c,v 1.16 2011/06/28 16:19:16 manu Exp $ */
+/* $NetBSD: perfuse.c,v 1.17 2011/08/09 06:58:33 manu Exp $ */
/*-
* Copyright (c) 2010-2011 Emmanuel Dreyfus. All rights reserved.
@@ -484,7 +484,25 @@
PUFFSOP_SET(pops, perfuse, node, deleteextattr);
#endif /* PUFFS_EXTNAMELEN */
- puffs_flags = PUFFS_KFLAG_WTCACHE;
+ /*
+ * We used to have PUFFS_KFLAG_WTCACHE here, which uses the
+ * page cache (highly desirable to get mmap(2)), but still sends
+ * all writes to the filesystem. In fact it does not send the
+ * data written, but the pages that contain it.
+ *
+ * There is a nasty bug hidden somewhere, possibly in libpuffs'
+ * VOP_FSYNC, which sends an asynchronous PUFFS_SETATTR that
+ * update file size. When writes are in progress, it will cause
+ * the file to be truncated and we get a zero-filled chunk at the
+ * beginning of a page. Removing PUFFS_KFLAG_WTCACHE fixes that
+ * problem.
+ *
+ * The other consequences are that changes will not be propagated
+ * immediatly to the filesystem, and we get a huge performance gain
+ * because much less requests are sent. A test case for the above
+ * mentioned bug got its execution time slashed by factor 50.
+ */
+ puffs_flags = 0;
if (perfuse_diagflags & PDF_PUFFS)
puffs_flags |= PUFFS_FLAG_OPDUMP;
