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Btrfs: tune btrfs unplug functions for a small number of devices 

When btrfs unplugs, it tries to find the correct device to unplug
via search through the extent_map tree.  This avoids unplugging
a device that doesn't need it, but is a waste of time for filesystems
with a small number of devices.

This patch checks the total number of devices before doing the
search.

Signed-off-by: Chris Mason <chris.mason@oracle.com>
This commit is contained in:
Chris Mason 2008-11-10 13:08:31 -05:00
parent b47eda8690
commit 240d5d482b
1 changed files with 10 additions and 0 deletions
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10
fs/btrfs/disk-io.c
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@ -1201,6 +1201,16 @@ void btrfs_unplug_io_fn(struct backing_dev_info *bdi, struct page *page)
return;
inode = mapping->host;
/*
* don't do the expensive searching for a small number of
* devices
*/
if (BTRFS_I(inode)->root->fs_info->fs_devices->open_devices <= 2) {
__unplug_io_fn(bdi, page);
return;
}
offset = page_offset(page);
em_tree = &BTRFS_I(inode)->extent_tree;