On tue, 6 Dec 2011 16:36:11 -0500, Chris Mason wrote: > On Tue, Dec 06, 2011 at 06:23:23AM -0500, Christoph Hellwig wrote: >> On Tue, Dec 06, 2011 at 07:06:40PM +0800, Miao Xie wrote: >>>> I can't see why you need the writeout when the trylocks fails. Umount >>>> needs to take care of writing out all pending file data anyway, so doing >>>> it from the cleaner thread in addition doesn't sound like it would help. >>> >>> umount invokes sync_fs() and write out all the dirty file data. For the >>> other file systems, its OK because the file system does not introduce dirty pages >>> by itself. But btrfs is different. Its automatic defragment will make lots of dirty >>> pages after sync_fs() and reserve lots of meta-data space for those pages. >>> And then the cleaner thread may find there is no enough space to reserve, it must >>> sync the dirty file data and release the reserved space which is for the dirty >>> file data. >> >> I think the safest way to fix is is to write out all dirty data again >> once the cleaner thread has been safely stopped. >> > > Said another way we want to stop the autodefrag code before the unmount > is ready to continue. We also want to stop balancing, scrub etc. But there is no good interface to do it before umount gets s_umount lock. I think trylock(in writeback_inodes_sb_nr_if_idle()) + dirty data flush can help us to fix the bug perfectly. Thanks Miao > > -chris > > -- > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- 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
