Messages in this thread | | | Date | Mon, 21 Sep 2009 21:10:57 +0800 | From | Wu Fengguang <> | Subject | Re: [PATCH] fs: Fix busyloop in wb_writeback() |
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On Mon, Sep 21, 2009 at 09:06:34PM +0800, Jens Axboe wrote: > On Mon, Sep 21 2009, Wu Fengguang wrote: > > On Thu, Sep 17, 2009 at 02:41:06AM +0800, Jens Axboe wrote: > > > On Wed, Sep 16 2009, Jan Kara wrote: > > > > 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. > > > > > > Interesting, so this will happen if the dirtier and flush thread end up > > > "fighting" each other over the same inode. I'll throw this into the > > > testing mix. > > > > > > How did you notice? > > > > Jens, I found another busy loop. Not sure about the solution, but here > > is the quick fact. > > > > Tested git head is 1ef7d9aa32a8ee054c4d4fdcd2ea537c04d61b2f, which > > seems to be the last writeback patch in the linux-next tree. I cannot > > run the plain head of linux-next because it just refuses boot up. > > > > On top of which Jan Kara's I_SYNC waiting patch and the attached > > debugging patch is applied. > > > > Test commands are: > > > > # mount /mnt/test # ext4 fs > > # echo 1 > /proc/sys/fs/dirty_debug > > > > # cp /dev/zero /mnt/test/zero0 > > > > After that the box is locked up, the system is busy doing these: > > > > [ 54.740295] requeue_io() +457: inode=79232 > > [ 54.740300] mm/page-writeback.c +539 balance_dirty_pages(): comm=cp pid=3327 n=0 > > [ 54.740303] global dirty=60345 writeback=10145 nfs=0 flags=_M towrite=1536 skipped=0 > > [ 54.740317] requeue_io() +457: inode=79232 > > [ 54.740322] mm/page-writeback.c +539 balance_dirty_pages(): comm=cp pid=3327 n=0 > > [ 54.740325] global dirty=60345 writeback=10145 nfs=0 flags=_M towrite=1536 skipped=0 > > [ 54.740339] requeue_io() +457: inode=79232 > > [ 54.740344] mm/page-writeback.c +539 balance_dirty_pages(): comm=cp pid=3327 n=0 > > [ 54.740347] global dirty=60345 writeback=10145 nfs=0 flags=_M towrite=1536 skipped=0 > > ...... > > > > Basically the traces show that balance_dirty_pages() is busy looping. > > It cannot write anything because the inode always be requeued by this line: > > > > if (inode->i_state & I_SYNC) { > > if (!wait) { > > requeue_io(inode); > > return 0; > > } > > > > This seem to happen when the partition is FULL. > > OK, I'll have to look into these issues soonish. I'll be travelling next > week though, so I cannot do more about it right now. If you have time to > work on tested patches, then that would be MUCH appreciated it!
Jens, your bug fix patches arrive just before I submit this bug report :)
Thanks, Fengguang
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