On Tue, Nov 16, 2010 at 10:30:37PM -0600, Eric Sandeen wrote: > On 11/16/10 7:01 AM, Jan Kara wrote: > > On Tue 16-11-10 22:00:58, Nick Piggin wrote: > >> I saw a lock order warning on ext4 trigger. This should solve it. > >> Raciness shouldn't matter much, because writeback can stop just > >> after we make the test and return anyway (so the API is racy anyway). > > Hmm, for now the fix is OK. Ultimately, we probably want to call > > writeback_inodes_sb() directly from all the callers. They all just want to > > reduce uncertainty of delayed allocation reservations by writing delayed > > data and actually wait for some of the writeback to happen before they > > retry again the allocation. > > For ext4, at least, it's just best-effort. We're not actually out of > space yet when this starts pushing. But it helps us avoid enospc: > > commit c8afb44682fcef6273e8b8eb19fab13ddd05b386 > Author: Eric Sandeen <sandeen@xxxxxxxxxx> > Date: Wed Dec 23 07:58:12 2009 -0500 > > ext4: flush delalloc blocks when space is low > > Creating many small files in rapid succession on a small > filesystem can lead to spurious ENOSPC; on a 104MB filesystem: > > for i in `seq 1 22500`; do > echo -n > $SCRATCH_MNT/$i > echo XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX > $SCRATCH_MNT/$i > done > > leads to ENOSPC even though after a sync, 40% of the fs is free > again. > > <snip> > > We don't need it to be synchronous - in fact I didn't think it was ... By synchronous, I just mean that the caller is the one who pushes the data into writeout. It _may_ be better if it was done by background writeback, with a feedback loop to throttle the caller (preferably placed outside any locks it is holding). To be pragmatic, I think the thing is fine to actually solve the problem at hand. I was just saying that it has a tiny little hackish feeling anyway, so a trylock will be right at home there :) > ext4 should probably use btrfs's new variant and just get rid of the > one I put in, for a very large system/filesystem it could end up doing > a rather insane amount of IO when the fs starts to get full. > > as for the locking problems ... sorry about that! That's no problem. So is that an ack? :) -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
