page-writeback: fix the calculation of the oldest_jif in wb_kupdate()

wb_kupdate() function has a bug on linux-2.6.30-rc5.  This bug causes
generic_sync_sb_inodes() to start to write inodes back much earlier than
our expectations because it miscalculates oldest_jif in wb_kupdate().

This bug was introduced in 704503d836042d4a4c7685b7036e7de0418fbc0f
('mm: fix proc_dointvec_userhz_jiffies "breakage"').

Signed-off-by: Toshiyuki Okajima <toshi.okajima@jp.fujitsu.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 30351f0063acb125f4581f0a1c6197662254d8ab..bb553c3e955da10631ca7f8229be2b1bdb791f25 100644 (file)
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -94,12 +94,12 @@ unsigned long vm_dirty_bytes;
 /*
  * The interval between `kupdate'-style writebacks
  */
-unsigned int dirty_writeback_interval = 5 * 100; /* sentiseconds */
+unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */
 
 /*
  * The longest time for which data is allowed to remain dirty
  */
-unsigned int dirty_expire_interval = 30 * 100; /* sentiseconds */
+unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */
 
 /*
  * Flag that makes the machine dump writes/reads and block dirtyings.
@@ -770,7 +770,7 @@ static void wb_kupdate(unsigned long arg)
 
        sync_supers();
 
-       oldest_jif = jiffies - msecs_to_jiffies(dirty_expire_interval);
+       oldest_jif = jiffies - msecs_to_jiffies(dirty_expire_interval * 10);
        start_jif = jiffies;
        next_jif = start_jif + msecs_to_jiffies(dirty_writeback_interval * 10);
        nr_to_write = global_page_state(NR_FILE_DIRTY) +