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fs: Fix busyloop in wb_writeback() 

If all inodes are under writeback (e.g. in case when there's only one inode
with dirty pages), wb_writeback() with WB_SYNC_NONE work basically degrades
to busylooping until I_SYNC flags of the inode is cleared. Fix the problem by
waiting on I_SYNC flags of an inode on b_more_io list in case we failed to
write anything.

Tested-by: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
This commit is contained in:
Jan Kara 2009-09-16 19:22:48 +02:00 committed by Jens Axboe
parent 7fa07729e4
commit a5989bdc98
1 changed files with 18 additions and 1 deletions
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19
fs/fs-writeback.c
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@ -706,6 +706,7 @@ static long wb_writeback(struct bdi_writeback *wb,
}; };
unsigned long oldest_jif; unsigned long oldest_jif;
long wrote = 0; long wrote = 0;
struct inode *inode;
if (wbc.for_kupdate) { if (wbc.for_kupdate) {
wbc.older_than_this = &oldest_jif; wbc.older_than_this = &oldest_jif;
@ -747,8 +748,24 @@ static long wb_writeback(struct bdi_writeback *wb,
* If we ran out of stuff to write, bail unless more_io got set * If we ran out of stuff to write, bail unless more_io got set
*/ */
if (wbc.nr_to_write > 0 || wbc.pages_skipped > 0) { if (wbc.nr_to_write > 0 || wbc.pages_skipped > 0) {
if (wbc.more_io && !wbc.for_kupdate) if (wbc.more_io && !wbc.for_kupdate) {
if (wbc.nr_to_write < MAX_WRITEBACK_PAGES)
continue;
/*
* Nothing written. Wait for some inode to
* become available for writeback. Otherwise
* we'll just busyloop.
*/
spin_lock(&inode_lock);
if (!list_empty(&wb->b_more_io)) {
inode = list_entry(
wb->b_more_io.prev,
struct inode, i_list);
inode_wait_for_writeback(inode);
}
spin_unlock(&inode_lock);
continue; continue;
}
break; break;
} }
} }