Commit 7d455e00 authored Aug 15, 2008 by Chris Mason Committed by Linus Torvalds Aug 15, 2008

fs/inode.c: properly init address_space->writeback_index

write_cache_pages() uses i_mapping->writeback_index to pick up where it
left off the last time a given inode was found by pdflush or
balance_dirty_pages (or anyone else who sets wbc->range_cyclic)

alloc_inode() should set it to a sane value so that writeback doesn't
start in the middle of a file. It is somewhat difficult to notice the bug
since write_cache_pages will loop around to the start of the file and the
elevator helps hide the resulting seeks.

For whatever reason, Btrfs hits this often. Unpatched, untarring 30
copies of the linux kernel in series runs at 47MB/s on a single sata
drive. With this fix, it jumps to 62MB/s.

Signed-off-by: Chris Mason <chris.mason@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 75312619

fs/inode.c

+1 −0

Original line number	Diff line number	Diff line
		@@ -166,6 +166,7 @@ static struct inode alloc_inode(struct super_block sb)
		mapping_set_gfp_mask(mapping, GFP_HIGHUSER_PAGECACHE);
		mapping->assoc_mapping = NULL;
		mapping->backing_dev_info = &default_backing_dev_info;
		mapping->writeback_index = 0;

		/*
		* If the block_device provides a backing_dev_info for client

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