Commit 06d6cf69 authored Jul 11, 2008 by Aneesh Kumar K.V Committed by Theodore Ts'o Jul 11, 2008

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>

parent d2a17637

include/linux/writeback.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -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;
		};

		/*

mm/page-writeback.c

+3 −0

Original line number	Diff line number	Diff line
		@@ -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);

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