[PATCH] writeback: fix range handling

When a writeback_control's `start' and `end' fields are used to
indicate a one-byte-range starting at file offset zero, the required
values of .start=0,.end=0 mean that the ->writepages() implementation
has no way of telling that it is being asked to perform a range
request.  Because we're currently overloading (start == 0 && end == 0)
to mean "this is not a write-a-range request".

To make all this sane, the patch changes range of writeback_control.

So caller does: If it is calling ->writepages() to write pages, it
sets range (range_start/end or range_cyclic) always.

And if range_cyclic is true, ->writepages() thinks the range is
cyclic, otherwise it just uses range_start and range_end.

This patch does,

    - Add LLONG_MAX, LLONG_MIN, ULLONG_MAX to include/linux/kernel.h
      -1 is usually ok for range_end (type is long long). But, if someone did,

		range_end += val;		range_end is "val - 1"
		u64val = range_end >> bits;	u64val is "~(0ULL)"

      or something, they are wrong. So, this adds LLONG_MAX to avoid nasty
      things, and uses LLONG_MAX for range_end.

    - All callers of ->writepages() sets range_start/end or range_cyclic.

    - Fix updates of ->writeback_index. It seems already bit strange.
      If it starts at 0 and ended by check of nr_to_write, this last
      index may reduce chance to scan end of file.  So, this updates
      ->writeback_index only if range_cyclic is true or whole-file is
      scanned.

Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Cc: Nathan Scott <nathans@sgi.com>
Cc: Anton Altaparmakov <aia21@cantab.net>
Cc: Steven French <sfrench@us.ibm.com>
Cc: "Vladimir V. Saveliev" <vs@namesys.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 75d7f48b79bb..8ccf6f1b1473 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -204,6 +204,7 @@ static void balance_dirty_pages(struct address_space *mapping)
                         .sync_mode      = WB_SYNC_NONE,
                         .older_than_this = NULL,
                         .nr_to_write    = write_chunk,
+                        .range_cyclic   = 1,
                 };
 
                 get_dirty_limits(&wbs, &background_thresh,
@@ -331,6 +332,7 @@ static void background_writeout(unsigned long _min_pages)
                 .older_than_this = NULL,
                 .nr_to_write    = 0,
                 .nonblocking    = 1,
+                .range_cyclic   = 1,
         };
 
         for ( ; ; ) {
@@ -407,6 +409,7 @@ static void wb_kupdate(unsigned long arg)
                 .nr_to_write    = 0,
                 .nonblocking    = 1,
                 .for_kupdate    = 1,
+                .range_cyclic   = 1,
         };
 
         sync_supers();