On 11/16/10 10:38 PM, Nick Piggin wrote: > 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? :) > I'd like to test it with the original case it was supposed to solve; will do that tomorrow. -Eric -- 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
