On Thu 05-05-11 20:14:02, Wu Fengguang wrote: > On Thu, May 05, 2011 at 05:00:59AM +0800, Jan Kara wrote: > > On Mon 02-05-11 11:17:51, Wu Fengguang wrote: > > > sync(2) is performed in two stages: the WB_SYNC_NONE sync and the > > > WB_SYNC_ALL sync. Tag the first stage with wbc.tagged_sync and do > > > livelock prevention for it, too. > > > > > > Note that writeback_inodes_sb() is called by not only sync(), they are > > > treated the same because the other callers need also need livelock > > > prevention. > > I was thinking about this and could not find any - which other callers > > of writeback_inodes_sb() need the livelock prevention? > > For example, the writeback_inodes_sb_if_idle() call from ext4. > In general anyone that pass get_nr_dirty_pages() as work->nr_pages > may be highly over-estimating the work set. OK, I see what you mean. I agree using tagging in these cases probably makes sense. > It won't be directly livelocked since ext4 won't wait for completion, > however there is possibility the works queued behind are delayed and > livelocked. Actually it will, writeback_inodes_sb() waits for completion (because of s_umount locking). ext4 should use writeback_inodes_sb_if_idle_nr() (with some relatively small number) anyway to avoid the pauses. > Ideally simple ->nr_pages works should be given lower priority and > even may be merged with each other, and that would be future work. Merging works wanting to do the same thing would be nice. I though about it some time ago for a while but getting all the combinations right and making the merging code resonably simple was hard so I postponed it for later because it was not urgent. Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
