On Tue, Jan 11, 2011 at 08:15:19AM +0800, Li, Shaohua wrote: > On Mon, 2011-01-10 at 22:26 +0800, Wu, Fengguang wrote: > > Shaohua, > > > > On Tue, Jan 04, 2011 at 01:40:30PM +0800, Li, Shaohua wrote: > > > 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 > > > > If that is the main obstacle, why not do straightforward fincore()/ > > fadvise(), and add ioctls to btrfs to export/grab the hidden > > btree_inode in any form? This will address btrfs' specific issue, and > > have the benefit of making the VFS part general enough. You know > > ext2/3/4 already have block_dev ready for metadata readahead. > I forgot to update this comment. Please see patch 2 and patch 4, both > incore and readahead need btrfs specific staff involved, so we can't use > generic fincore or something. You can if you like :) - fincore() can return the referenced bit, which is generally useful information - btrfs_metadata_readahead() can be passed to some (faked) ->readpages() for use with fadvise. Thanks, Fengguang > > > 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 > > -- 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
