Hi, We have file readahead to do asyn file read, but has no metadata readahead. For a list of files, their metadata is stored in fragmented disk space and metadata read is a sync operation, which impacts the efficiency of readahead much. The patches try to add meatadata readahead for btrfs. In btrfs, metadata is stored in btree_inode. Ideally, if we could hook the inode to a fd so we could use existing syscalls (readahead, mincore or upcoming fincore) to do readahead, but the inode is hidden, there is no easy way for this from my understanding. So we add two ioctls for this. One is like readahead syscall, the other is like micore/fincore syscall. Under a harddisk based netbook with Meego, the metadata readahead reduced about 3.5s boot time in average from total 16s. Last time I posted similar patches to btrfs maillist, which adds the new ioctls in btrfs specific ioctl code. But Christoph Hellwig asks we have a generic interface to do this so other filesystem can share some code, so I came up with the new one. Comments and suggestions are welcome! v1->v2: 1. Added more comments and fix return values suggested by Andrew Morton 2. fix a race condition pointed out by Yan Zheng initial post: http://marc.info/?l=linux-fsdevel&m=129222493406353&w=2 Thanks, Shaohua -- 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
