On Tue, Sep 15 2009, Jan Kara wrote: > On Mon 14-09-09 20:36:54, Jens Axboe wrote: > > On Mon, Sep 14 2009, Trond Myklebust wrote: > > > On Mon, 2009-09-14 at 15:02 +0200, Jan Kara wrote: > > > > On Mon 14-09-09 11:36:29, Jens Axboe wrote: > > > > > We do this automatically in get_sb_bdev() from the set_bdev_super() > > > > > callback. Filesystems that have their own private backing_dev_info > > > > > must assign that in ->fill_super(). > > > > > > > > > > Note that ->s_bdi assignment is required for proper writeback! > > > > > > > > > > Acked-by: Christoph Hellwig <hch@xxxxxxxxxxxxx> > > > > > Signed-off-by: Jens Axboe <jens.axboe@xxxxxxxxxx> > > > > Hmm, looking at this again, I'm not sure this will work for NFS. It seems > > > > to set mapping->backing_dev_info to its private backing dev info for > > > > regular files while it leaves it intact for other inodes (e.g. > > > > directories). I'm not sure why it does so but it seems its inodes end up on > > > > two different BDI lists and thus they wouldn't be synced properly. Trond, > > > > do I read the code properly? > > > > Also we definitely need to set *some* bdi in nfs_get_sb as otherwise sync > > > > won't work for it. > > > > > > There hasn't really been a need for a bdi in NFS other than for the > > > regular file read and writeback code. The main reason for making it > > > private was to ensure that we could set a per-superblock readahead limit > > > that was a decent multiple of the server's preferred read block size. > > > > > > Is there any reason why we couldn't set sb->s_bdi to point to that > > > private bdi? > > > > No, that should work fine. NFS already works fine with the bdi flusher > > threads, so you should just point it at that bdi. > But will it really work well? I mean if we sync the superblock on the > client, it will sync only the private BDI. So it won't sync any directory > inodes because they are on the default_backing_dev_info (NFS leaves > sb->s_bdev at NULL). No you are right, it wont be complete. I talked to Chris about this yesterday, and we agree that the best option is to give NFS the 'btrfs treatment' bdi wise. -- Jens Axboe -- 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
