mm: Add range_cont mode for writeback

Filesystems like ext4 needs to start a new transaction in
the writepages for block allocation. This happens with delayed
allocation and there is limit to how many credits we can request
from the journal layer. So we call write_cache_pages multiple
times with wbc->nr_to_write set to the maximum possible value
limitted by the max journal credits available.

Add a new mode to writeback that enables us to handle this
behaviour. In the new mode we update the wbc->range_start
to point to the new offset to be written. Next call to
call to write_cache_pages will start writeout from specified
range_start offset. In the new mode we also limit writing
to the specified wbc->range_end.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Mingming Cao <cmm@us.ibm.com>
Acked-by: Jan Kara <jack@suse.cz>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index f462439cc2886c56f7c1940f4100ba726d4068c4..0d8573e6b9ec24364bbab8c6c1e827946e483c58 100644 (file)
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -63,6 +63,7 @@ struct writeback_control {
        unsigned for_writepages:1;      /* This is a writepages() call */
        unsigned range_cyclic:1;        /* range_start is cyclic */
        unsigned more_io:1;             /* more io to be dispatched */
+       unsigned range_cont:1;
 };
 
 /*

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 789b6adbef37f1f38c3887f10ba130595903408a..ded57d52806052deb17a5fdadbda6dac3dca9799 100644 (file)
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -956,6 +956,9 @@ retry:
        }
        if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
                mapping->writeback_index = index;
+
+       if (wbc->range_cont)
+               wbc->range_start = index << PAGE_CACHE_SHIFT;
        return ret;
 }
 EXPORT_SYMBOL(write_cache_pages);