mm: Add range_cont mode for writeback From: Aneesh Kumar K.V 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 Signed-off-by: Mingming Cao Acked-by: Jan Kara Signed-off-by: "Theodore Ts'o" --- include/linux/writeback.h | 1 + mm/page-writeback.c | 3 +++ 2 files changed, 4 insertions(+) Index: linux-2.6.26-rc9/include/linux/writeback.h =================================================================== --- linux-2.6.26-rc9.orig/include/linux/writeback.h 2008-07-11 16:04:27.000000000 -0700 +++ linux-2.6.26-rc9/include/linux/writeback.h 2008-07-11 16:05:13.000000000 -0700 @@ -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; }; /* Index: linux-2.6.26-rc9/mm/page-writeback.c =================================================================== --- linux-2.6.26-rc9.orig/mm/page-writeback.c 2008-07-11 16:04:27.000000000 -0700 +++ linux-2.6.26-rc9/mm/page-writeback.c 2008-07-11 16:05:13.000000000 -0700 @@ -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);